EXHIBIT 4.1

SEVENTEENTH SUPPLEMENTAL INDENTURE

THIS SEVENTEENTH SUPPLEMENTAL INDENTURE, dated as of September 23, 2019 (this “Supplemental Indenture”), is between MPLX LP, a limited partnership duly formed and existing under the laws of the State of Delaware (the “Partnership”), and The Bank of New York Mellon Trust Company, N.A., a national banking association, as trustee (the “Trustee”).

WITNESSETH

WHEREAS, pursuant to the Senior Indenture, dated as of February 12, 2015 (the “Base Indenture”), as supplemented by the First Supplemental Indenture, dated as of February 12, 2015, the Second Supplemental Indenture, dated as of December 22, 2015, the Third Supplemental Indenture, dated as of December 22, 2015, the Fourth Supplemental Indenture, dated as of December 22, 2015, the Fifth Supplemental Indenture, dated as of December 22, 2015, the Sixth Supplemental Indenture, dated as of February 10, 2017, the Seventh Supplemental Indenture, dated as of February 10, 2017, the Eighth Supplemental Indenture, dated as of February 8, 2018, the Ninth Supplemental Indenture, dated as of February 8, 2018, the Tenth Supplemental Indenture, dated as of February 8, 2018, the Eleventh Supplemental Indenture, dated as of February 8, 2018, the Twelfth Supplemental Indenture, dated as of February 8, 2018, the Thirteenth Supplemental Indenture, dated as of November 15, 2018, the Fourteenth Supplemental Indenture, dated as of November 15, 2018, the Fifteenth Supplemental Indenture, dated as of September 9, 2019, and the Sixteenth Supplemental Indenture, dated as of September 9, 2019 (as so supplemented, the “Indenture”), in each case between the Partnership and the Trustee, the Partnership may from time to time issue and sell Debt Securities in one or more series;

WHEREAS, the Partnership desires to create and authorize a new series of Debt Securities entitled “6.250% Senior Notes due 2022” (the “Notes”), limited initially to $266,382,000 in aggregate principal amount, and to provide the terms and conditions upon which the Notes are to be executed, registered, authenticated, issued and delivered, the Partnership has duly authorized the execution and delivery of this Supplemental Indenture;

WHEREAS, the Notes are a series of Debt Securities and are being issued under the Indenture, as supplemented by this Supplemental Indenture, and are subject to the terms contained therein and herein;

WHEREAS, the Notes are to be substantially in the form attached hereto as Exhibit A; and

WHEREAS, all acts and things necessary to make the Notes, when executed by the Partnership and authenticated and delivered by or on behalf of the Trustee as provided in the Indenture and this Supplemental Indenture, the valid, binding and legal obligations of the Partnership, and to make this Supplemental Indenture a legal, binding and enforceable agreement, have been done and performed.

NOW, THEREFORE, in order to declare the terms and conditions upon which the Notes are executed, registered, authenticated, issued and delivered, and in consideration of the foregoing premises and the purchase of such Notes by the Holders thereof, the Partnership and the Trustee mutually covenant and agree, for the equal and proportionate benefit of the Holders from time to time of the Notes, as follows:

Section 1. Definitions. Terms used in this Supplemental Indenture and not defined herein shall have the respective meanings given such terms in the Indenture.

Section 2. Other Definitions. In addition, the following terms shall have the following meanings with respect to the Notes:

“Additional Interest” means “Additional Interest” payable pursuant to the Registration Rights Agreement.

“Board Resolution” means a copy of a resolution or resolutions of the Board of Directors, certified by the Secretary or an Assistant Secretary of the General Partner to be in full force and effect on the date of such certification, and delivered to the Trustee.

“Clearstream” means Clearstream Banking, société anonyme, or any successor securities clearing agency.

“Consolidated Net Tangible Assets” means the aggregate value of all assets of the Partnership and its Subsidiaries after deducting therefrom: (i) all current liabilities, excluding all short-term indebtedness and the current portion of long-term indebtedness; (ii) all investments in unconsolidated subsidiaries and all investments accounted for on the equity basis; and (iii) all goodwill patents and trademarks, unamortized debt discounts and other similar intangibles (all determined in conformity with generally accepted accounting principles and calculated on a basis consistent with the Partnership’s most recent audited consolidated financial statements).

“Euroclear” means Euroclear Bank S.A./N.V., as operator of Euroclear systems Clearance System or any successor securities clearing agency.

“Exchange Global Notes” has the meaning set forth in Section 7(a) herein.

“Exchange Notes” means any notes issued in exchange for Notes pursuant to the Registration Rights Agreement or similar agreement.

“Global Notes” has the meaning set forth in Section 7(c) herein.

“Interest Payment Date,” when used with respect to any installment of interest on any Debt Security, means the date specified in such Debt Security as the fixed date on which such installment of interest is due and payable.

“Mortgage” means as the context may require, (i) to mortgage, pledge, encumber or subject to a lien or (ii) a mortgage, pledge, encumbrance or lien.

2

“Predecessor Security” of any particular Debt Security means every previous Debt Security evidencing all or a portion of the same debt as that evidenced by such particular Debt Security; and, for the purposes of this definition, any Debt Security authenticated and delivered under Section 2.09 of the Base Indenture in exchange for or in lieu of a mutilated, destroyed, lost or stolen Debt Security shall be deemed to evidence the same debt as the mutilated, destroyed, lost or stolen Debt Security.

“QIB” means a “qualified institutional buyer” as defined in Rule 144A.

“Registration Rights Agreement” means the registration rights agreement, dated as of the date of this Supplemental Indenture, by and among the Partnership, the General Partner, Barclays Capital Inc., MUFG Securities Americas Inc. and Wells Fargo Securities, LLC.

“Regular Record Date” for the interest payable on any Interest Payment Date on the Debt Securities means the date specified for that purpose as contemplated by Section 2.03 of the Base Indenture.

“Regulation S” means Regulation S promulgated under the Securities Act.

“Regulation S Global Notes” has the meaning set forth in Section 7(c) herein.

“Regulation S Notes” has the meaning set forth in Section 7(c) herein.

“Restricted Notes Legend” has the meaning set forth in Section 7(d) herein.

“Restricted Period” has the meaning set forth in Section 7(c) herein.

“Rule 144” means Rule 144 promulgated under the Securities Act.

“Rule 144A” means Rule 144A promulgated under the Securities Act.

“Rule 144A Global Notes” has the meaning set forth in Section 7(b) herein.

“Rule 144A Notes” has the meaning set forth in Section 7(b) herein.

“Special Record Date” for the payment of any Defaulted Interest means a date fixed by the Trustee pursuant to Section 2.17 of the Base Indenture.

“Transfer Restricted Note” means any Note that bears or is required to bear the Restricted Notes Legend.

“U.S. person” means a “U.S. person” as defined in Regulation S.

3

Section 3. Creation and Authorization of Series.

(a) There is hereby created and authorized the following new series of Debt Securities to be issued under the Indenture, to be designated as the “6.250% Senior Notes due 2022.”

(b) The Notes shall be limited initially to $266,382,000 in aggregate principal amount. Notwithstanding the foregoing initial aggregate principal amount, the Partnership may, from time to time, without notice to or consent of the Holders of the Notes, increase the principal amount of the Notes that may be issued under this Supplemental Indenture and issue such increased principal amount (or any portion thereof), in which case any additional Notes so issued will have the same terms and conditions other than the public offering price, original interest accrual date and initial interest payment date, and the same CUSIP numbers as the applicable series of Notes previously issued, will be fungible with the applicable series of Notes previously issued for U.S. federal income tax purposes, and will carry the same right to receive accrued and unpaid interest as the Notes previously issued, and such additional notes will form a single series with the Notes of such series previously issued, including, without limitation, for purposes of waivers, amendments, redemptions and, if any, offers to purchase, and will rank equally and ratably with the Notes of such series previously issued.

(c) The date on which the principal is payable on the Notes, unless accelerated pursuant to the Indenture, shall be as provided in the form of security attached hereto as Exhibit A.

(d) The Notes shall bear interest as provided in the form of security attached hereto as Exhibit A. The Interest Payment Dates and the Regular Record Dates for the determination of Holders of the Notes to whom such interest is payable shall be as provided in the form of security attached hereto as Exhibit A. Additional Interest, if any, will be payable in arrears on each Interest Payment Date following accrual in the same manner as regular interest on the Notes.

(e) The Notes shall be redeemable at the option of the Partnership as set forth in the form of security attached hereto as Exhibit A.

(f) The provisions of Sections 3.04 and 3.05 of the Base Indenture shall not be applicable to the Notes.

(g) The Notes will be issued only in fully registered form, without coupons, in denominations provided herein and in the form of security attached hereto as Exhibit A.

(h) The Events of Default and covenants specified in the Indenture will apply to the Notes.

(i) The defeasance and covenant defeasance provisions of Article XI of the Indenture, including both Sections 11.02 and 11.03 of the Base Indenture, will apply to the Notes.

(j) The Notes shall be issued in the form of one or more Global Securities substantially in the form of security attached hereto as Exhibit A. The Partnership initially appoints The Depository Trust Company to act as Depositary with respect to the Notes. Additional provisions applicable to the Notes issued in the form of a Global Security are set forth in the form of security attached hereto as Exhibit A.

4

(k) The Notes shall be issuable only in denominations of $2,000 and integral multiples of $1,000 in excess thereof.

(l) The Trustee will initially act as the Registrar for the Notes and as the paying agent with respect to the Notes. The Place of Payment will be The Bank of New York Mellon Trust Company, N.A., 240 Greenwich Street, New York, New York 10286.

(m) Except as otherwise set forth herein and in the Notes, the terms of the Notes shall be as set forth in the Indenture, including those made part of the Indenture by reference to the TIA.

Section 4. Additional Covenants. In addition to the covenants set forth in Article IV of the Indenture, the following additional covenants shall apply with respect to the Notes:

Section 4.10 Mortgage of Certain Property.

If the Partnership or any Subsidiary of the Partnership shall Mortgage as security for any indebtedness for money borrowed any pipeline, terminal or other logistics or storage property or asset employed in the transportation, distribution, storage, terminalling, processing or marketing of crude oil, natural gas, condensate or refined products that (i) is located in the United States and (ii) is determined to be a principal property by the Board of Directors in its discretion, the Partnership will secure, or will cause such Subsidiary to secure, the Notes and all other Debt Securities equally and ratably with all indebtedness or obligations secured by the Mortgage then being given; provided, however, that this covenant shall not apply in the case of:

5

Notwithstanding the foregoing restriction contained in this Section 4.10, the Partnership may and may permit its Subsidiaries to incur liens or grant Mortgages on property covered by the restriction above so long as the net book value of the property so encumbered, together with all property subject to the restriction on sale and leasebacks contained in Section 4.11, does not, at the time such lien or Mortgage is granted, exceed fifteen percent (15%) of Consolidated Net Tangible Assets.

Section 4.11 Sale and Leaseback of Certain Properties.

The Partnership will not, nor will it permit any Subsidiary of the Partnership to, sell or transfer any pipeline, terminal or other logistics or storage property or asset employed in the transportation, distribution, storage, terminalling, processing or marketing of crude oil, natural gas, condensate or refined products that (i) is located in the United States and (ii) is determined to be a principal property by the Board of Directors in its discretion, with the intention of taking back a lease of such property; provided, however, this covenant shall not apply if:

6

In the event of such a sale or transfer, the Partnership shall deliver to the Trustee the Board Resolution referred to in the parenthetical phrase contained in subclause (4)(B) of this Section 4.11 and an Officer’s Certificate setting forth all material facts under this Section 4.11.

For the purposes of this Section 4.11, the term retirement of such funded debt shall include the “in substance defeasance” of such funded debt in accordance with then applicable accounting rules.

Section 5. Consolidation, Merger, Sale or Conveyance. With respect to the Notes, Section 10.01 of the Base Indenture shall be amended to include the following language at the end of such section:

For purposes of this Section 10.01, “substantially all of its assets” shall mean, at any date, a portion of the non-current assets reflected in the Partnership’s consolidated balance sheet as of the end of the most recent quarterly period that represents at least sixty-six and two-thirds percent (66 2/3%) of the total reported value of such assets.

7

Section 6. Transfer Restrictions.

(a) The initial offering and sale of the Notes shall not be registered under the Securities Act or any state securities laws. The Notes shall be offered pursuant to exemptions from the registration requirements of the Securities Act in reliance upon Rule 144A and Regulation S promulgated under the Securities Act. For so long as any of the Notes constitute “restricted securities” within the meaning of Rule 144(a)(3) promulgated under the Securities Act, the Partnership shall, if the Partnership is not then subject to the reporting requirements of Section 13 or 15(d) of the Exchange Act, furnish to any Holder or beneficial owner of such Notes, or to any prospective purchaser of such Notes designated by such Holder or beneficial owner, in each case upon the written request of such Holder, beneficial owner or prospective purchaser, the information required to be provided pursuant to Rule 144A(d)(4) promulgated under the Securities Act.

(b) The following provisions shall apply with respect to any proposed transfer of any Transfer Restricted Note prior to the expiration of the holding period applicable to sales of such Notes under Rule 144, and the Registrar shall refuse to register any transfer of such Notes not complying with the restrictions set forth in the Restricted Notes Legend and in this Section 6. In addition to the requirements set forth in Section 2.07 of the Base Indenture, Transfer Restricted Notes that are presented or surrendered for registration of transfer or exchange pursuant to Section 2.07 of the Base Indenture shall be accompanied by the following additional information and documents, as applicable, upon which the Registrar may conclusively rely:

(i) if such Transfer Restricted Notes are being delivered to the Registrar by a Holder for registration in the name of such Holder, without transfer, a certification from such Holder to that effect (in substantially the form of Exhibit B hereto);

(ii) if such Transfer Restricted Notes are being transferred (1) to a QIB in accordance with Rule 144A or (2) pursuant to an effective registration statement under the Securities Act, a certification to that effect from such Holder (in substantially the form of Exhibit B hereto);

(iii) if such Transfer Restricted Notes are being transferred pursuant to an exemption from registration in accordance with Rule 903 or Rule 904 of Regulation S, certifications to that effect from such Holder (in substantially the form of Exhibit B and Exhibit C hereto) and an opinion of counsel to that effect if the Partnership or the Trustee so requests; or

(iv) if such Transfer Restricted Notes are being transferred in reliance on and in compliance with (1) an exemption from registration in accordance with Rule 144 under the Securities Act or (2) another exemption from the registration requirements of the Securities Act, a certification to that effect from such Holder (in substantially the form of Exhibit B attached hereto) and an opinion of counsel, certification or other evidence as may reasonably be required to that effect if the Partnership or the Trustee so requests.

8

(c) A Holder of a beneficial interest in a Regulation S Global Note who wishes to transfer its interest in such Note to a QIB in accordance with Rule 144A who takes delivery in the form of a beneficial interest in the Rule 144A Global Note shall deliver to the Registrar a certification to that effect (in substantially the form of Exhibit B attached hereto) upon which the Registrar may conclusively rely. After the expiration of the Restricted Period, interests in the Regulation S Global Note may be transferred without requiring the certification set forth in this Section 6(c).

(d) The transfer and exchange of Global Notes or beneficial interests therein shall be effected through the Depositary, in accordance with Section 2.07 of the Base Indenture and Section 6 and Section 7 hereof (including the restrictions on transfer set forth therein and herein) and the rules and procedures of the Depositary therefor, which shall include restrictions on transfer comparable to those set forth therein and herein to the extent required by the Securities Act; provided, however, that prior to the expiration of the Restricted Period, transfers and exchanges of beneficial interests in the Regulation S Global Note may be made pursuant to such restrictions only (1) to a Person that is not a U.S. person or for the account or benefit of a Person that is not a U.S. person within the meaning of Regulation S under the Securities Act or (2) to a QIB, in each case that hold such interests through Euroclear or Clearstream.

(e) If Notes are issued upon the registration of transfer, exchange or replacement of Notes not bearing the Restricted Notes Legend, the Notes so issued shall not bear such legend. If Notes are issued upon the registration or transfer, exchange or replacement of Notes bearing the Restricted Notes Legend, or if a request is made to remove the Restricted Notes Legend on a Note, the Notes so issued shall bear the Restricted Notes Legend, or the Restricted Notes Legend shall not be removed, as the case may be, unless there is delivered to the Partnership such satisfactory evidence, which may include an opinion of counsel of recognized standing licensed to practice law in the State of New York and experienced in matters involving the Securities Act, as may be reasonably required by the Partnership that neither the Restricted Notes Legend nor the restrictions on transfer set forth therein are required to ensure that transfers thereof comply with the provisions of Rule 144A, Rule 144 or Regulation S, that such Notes are not “restricted securities” within the meaning of Rule 144 or that such Notes were transferred pursuant to an effective registration statement under the Securities Act. Upon provision of such satisfactory evidence, the Trustee, at the direction of the Partnership, shall authenticate and deliver a Note that does not bear the Restricted Notes Legend. If a Restricted Notes Legend is removed from the face of a Note and the Note is subsequently held by an Affiliate of the Partnership, the Restricted Notes Legend shall be reinstated.

(f) Neither the Trustee nor the Registrar shall have any obligation or duty to monitor, determine or inquire as to compliance with any restrictions on transfer imposed under this Supplemental Indenture or under applicable law with respect to any transfer of any interest in any Note (including any transfers between or among Depositary participants or beneficial owners of interests in any Global Note) other than to require delivery of such certificates and other documentation or evidence as are expressly required by, and to do so only if and when expressly required by the terms of, this Supplemental Indenture, and to examine the same to determine substantial compliance as to form with the express requirements hereof. Notwithstanding anything herein to the contrary, neither the Trustee nor the Registrar shall have any responsibility to receive any letters, opinions or certifications, nor any responsibility to monitor compliance with any transfer restrictions, in connection with any transfer or exchange of any beneficial interest in a Global Note for a beneficial interest in the same Global Note.

9

(g) Notwithstanding the foregoing, in the event that any Transfer Restricted Notes are exchanged for Exchange Notes in connection with an effective registration statement pursuant to the Registration Rights Agreement, the Partnership shall issue and, at the direction of the Partnership, the Trustee shall authenticate the Exchange Notes in exchange for Transfer Restricted Notes accepted for exchange in the exchange offer, which Exchange Notes shall not bear the Restricted Notes Legend, and the Registrar shall rescind any restriction on the transfer of such Exchange Notes.

Section 7. Form of Notes/Legends.

(a) The Notes are being offered only to (A) Persons reasonably believed to be QIBs in reliance on Rule 144A and (B) non-U.S. persons in reliance on Regulation S. Such Notes may thereafter be transferred to, among others, QIBs, and purchasers in reliance on Regulation S, in each case, in accordance with the procedures described herein. Exchange Notes exchanged for interests in the Rule 144A Notes and the Regulation S Notes will be issued in the form of permanent global notes deposited with the Trustee as hereinafter provided, including the appropriate legend set forth in the form of security attached as Exhibit A (the “Exchange Global Notes”). The Exchange Global Notes will be deposited upon issuance with, or on behalf of, the Trustee as custodian for the Depositary, duly executed by the Partnership and authenticated by the Trustee as hereinafter provided. The Exchange Global Notes may be represented by more than one certificate, if so required by the Depositary’s rules regarding the maximum principal amount to be represented by a single certificate.

(b) The Notes offered to QIBs in the United States of America in reliance on Rule 144A (the “Rule 144A Notes”) shall be issued in the form of a permanent global note including appropriate legends as set forth in the form of security attached as Exhibit A (the “Rule 144A Global Notes”), deposited with the Trustee, as custodian for the Depositary, duly executed by the Partnership and authenticated by the Trustee as hereinafter provided. The Rule 144A Global Notes may be represented by more than one certificate, if so required by the Depositary’s rules regarding the maximum principal amount to be represented by a single certificate. The aggregate principal amount of the Rule 144A Global Notes may from time to time be increased or decreased by adjustments made on the records of the Trustee, as custodian for the Depositary, or its nominee, as hereinafter provided.

(c) The Notes offered to non-U.S. persons outside the United States of America (the “Regulation S Notes”) in reliance on Regulation S shall be issued in the form of a permanent global note including appropriate legends as set forth in the form of security attached as Exhibit A (the “Regulation S Global Notes” and, together with the Rule 144A Global Notes and the Exchange Global Notes, the “Global Notes”). Each Regulation S Global Note will be deposited upon issuance with, or on behalf of, the Trustee as custodian for the Depositary. Prior to the 40th day after the date the Notes are issued (such period through and including such 40th day, the “Restricted Period”), interests in the Regulation S Global Notes may only be transferred to non-U.S. persons pursuant to Regulation S, unless exchanged for interests in a Global Note in

10

accordance with the transfer and certification requirements described herein. Investors may hold their interests in the Regulation S Global Note through organizations other than Euroclear or Clearstream that are participants in the Depositary’s system or directly through Euroclear or Clearstream, if they are participants in such systems, or indirectly through organizations which are participants in such systems. If such interests are held through Euroclear or Clearstream, Euroclear and Clearstream will hold such interests in the applicable Regulation S Global Note on behalf of their participants through customers’ securities accounts in their respective names on the books of their respective depositaries. Such depositaries, in turn, will hold such interests in the applicable Regulation S Global Note in customers’ securities accounts in the depositaries’ names on the books of the Depositary. The Regulation S Global Notes may be represented by more than one certificate, if so required by the Depositary’s rules regarding the maximum principal amount to be represented by a single certificate. The aggregate principal amount of the Regulation S Global Notes may from time to time be increased or decreased by adjustments made on the records of the Trustee, as custodian for the Depositary or its nominee, as hereinafter provided.

(d) Unless and until (i) a Note issued as a Transfer Restricted Note is sold under an effective registration statement, (ii) a Note issued as a Transfer Restricted Note is exchanged for an Exchange Note in connection with an effective registration statement pursuant to the Registration Rights Agreement or (iii) the Partnership receives an opinion of counsel satisfactory to it to the effect that neither such legend nor the related restrictions on transfer are required in order to maintain compliance with the provisions of the Securities Act:

(1) each Transfer Restricted Note shall bear the following legend on the face thereof (the “Restricted Notes Legend”):

THIS NOTE HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”), AND MAY NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED EXCEPT IN ACCORDANCE WITH THE FOLLOWING SENTENCE. BY ITS ACQUISITION HEREOF OR OF A BENEFICIAL INTEREST HEREIN, THE ACQUIRER (1) REPRESENTS THAT (A) IT AND ANY ACCOUNT FOR WHICH IT IS ACTING IS A “QUALIFIED INSTITUTIONAL BUYER” (WITHIN THE MEANING OF RULE 144A UNDER THE SECURITIES ACT) AND THAT IT EXERCISES SOLE INVESTMENT DISCRETION WITH RESPECT TO EACH SUCH ACCOUNT, OR (B) IT IS NOT A “U.S. PERSON” (WITHIN THE MEANING OF REGULATION S UNDER THE SECURITIES ACT) AND (2) AGREES FOR THE BENEFIT OF MPLX LP THAT IT WILL NOT OFFER, SELL, PLEDGE OR OTHERWISE TRANSFER THIS NOTE OR ANY BENEFICIAL INTEREST HEREIN, EXCEPT IN ACCORDANCE WITH THE SECURITIES ACT AND ANY APPLICABLE SECURITIES LAWS OF ANY STATE OF THE UNITED STATES AND ONLY (A) TO MPLX LP, (B) PURSUANT TO A REGISTRATION STATEMENT WHICH HAS BECOME EFFECTIVE UNDER THE SECURITIES ACT, (C) TO A QUALIFIED INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A UNDER THE SECURITIES ACT, (D) IN AN OFFSHORE TRANSACTION IN COMPLIANCE WITH RULE 904 OF REGULATION S UNDER THE SECURITIES ACT, OR (E) PURSUANT TO AN EXEMPTION FROM REGISTRATION PROVIDED BY RULE 144 UNDER THE SECURITIES ACT OR ANY OTHER AVAILABLE EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.

11

PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (2)(C) ABOVE OR (2)(D) ABOVE, A DULY COMPLETED AND SIGNED CERTIFICATE (THE FORM OF WHICH MAY BE OBTAINED FROM THE TRUSTEE) MUST BE DELIVERED TO THE TRUSTEE. PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (E) ABOVE, MPLX LP RESERVES THE RIGHT TO REQUIRE THE DELIVERY OF SUCH LEGAL OPINIONS, CERTIFICATIONS OR OTHER EVIDENCE AS MAY REASONABLY BE REQUIRED IN ORDER TO DETERMINE THAT THE PROPOSED TRANSFER IS BEING MADE IN COMPLIANCE WITH THE SECURITIES ACT AND APPLICABLE STATE SECURITIES LAWS. NO REPRESENTATION IS MADE AS TO THE AVAILABILITY OF ANY RULE 144 EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.

(2) each Global Note shall bear the following legend on the face thereof:

UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (“DTC”), NEW YORK, NEW YORK, TO THE PARTNERSHIP OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO., OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

TRANSFERS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS IN WHOLE, BUT NOT IN PART, TO NOMINEES OF DTC OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR’S NOMINEE AND TRANSFERS OF PORTIONS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN THE INDENTURE REFERRED TO HEREIN.

Section 8. Effect of Supplemental Indenture. The provisions of this Supplemental Indenture are intended to supplement those of the Indenture as in effect immediately prior to the execution and delivery hereof. The Indenture shall remain in full force and effect except to the extent that the provisions of the Indenture are expressly modified by the terms of this Supplemental Indenture.

Section 9. Governing Law. This Supplemental Indenture and the Notes shall be governed by and construed in accordance with the law of the State of New York, without giving effect to any principles of conflicts of laws thereunder to the extent the application of the laws of another jurisdiction would be required thereby.

12

Section 10. Trustee Not Responsible for Recitals or Issuance of Notes. The recitals and statements contained herein shall be taken as statements of the Partnership, and the Trustee assumes no responsibility for their correctness. The Trustee makes no representations as to the validity or sufficiency of this Supplemental Indenture or of the Notes other than with respect to the Trustee’s execution of this Supplemental Indenture and authentication of the Notes. The Trustee shall not be accountable for the use or application by the Partnership of the Notes or the proceeds thereof.

Section 11. Conflict with the TIA. If any provision hereof limits, qualifies or conflicts with a provision of the TIA that is required under the TIA to be a part of and govern this Supplemental Indenture, the latter provision shall control. If any provision of this Supplemental Indenture modifies or excludes any provision of the TIA that may be so modified or excluded, the latter provision shall be deemed to apply to this Supplemental Indenture as so modified or to be excluded, as the case may be.

Section 12. Counterparts. This Supplemental Indenture may be executed in any number of counterparts, each of which shall be an original; but such counterparts shall together constitute one and the same instrument. The exchange of copies of this Supplemental Indenture and of signature pages by facsimile or electronic (i.e., “pdf” or “tif”) transmission shall constitute effective execution and delivery of this Supplemental Indenture for all purposes. Signatures of the parties hereto transmitted by facsimile or electronic (i.e., “pdf” or “tif”) transmission shall be deemed to be their original signatures for all purposes of the Supplemental Indenture as to the parties hereto and may be used in lieu of the original.

[The remainder of this page is left blank intentionally]

13

IN WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture to be duly executed as of the day and year first above written.

[Signature Page to Seventeenth Supplemental Indenture]

[Signature Page to Seventeenth Supplemental Indenture]

Exhibit A

MPLX LP

6.250% Senior Notes due 2022

[FOR GLOBAL NOTES: UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (“DTC”), NEW YORK, NEW YORK, TO THE PARTNERSHIP OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO., OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

TRANSFERS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS IN WHOLE, BUT NOT IN PART, TO NOMINEES OF DTC OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR’S NOMINEE AND TRANSFERS OF PORTIONS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN THE INDENTURE REFERRED TO HEREIN.]

[FOR TRANSFER RESTRICTED NOTES: THIS NOTE HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”), AND MAY NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED EXCEPT IN ACCORDANCE WITH THE FOLLOWING SENTENCE. BY ITS ACQUISITION HEREOF OR OF A BENEFICIAL INTEREST HEREIN, THE ACQUIRER (1) REPRESENTS THAT (A) IT AND ANY ACCOUNT FOR WHICH IT IS ACTING IS A “QUALIFIED INSTITUTIONAL BUYER” (WITHIN THE MEANING OF RULE 144A UNDER THE SECURITIES ACT) AND THAT IT EXERCISES SOLE INVESTMENT DISCRETION WITH RESPECT TO EACH SUCH ACCOUNT, OR (B) IT IS NOT A “U.S. PERSON” (WITHIN THE MEANING OF REGULATION S UNDER THE SECURITIES ACT) AND (2) AGREES FOR THE BENEFIT OF MPLX LP THAT IT WILL NOT OFFER, SELL, PLEDGE OR OTHERWISE TRANSFER THIS NOTE OR ANY BENEFICIAL INTEREST HEREIN, EXCEPT IN ACCORDANCE WITH THE SECURITIES ACT

AND ANY APPLICABLE SECURITIES LAWS OF ANY STATE OF THE UNITED STATES AND ONLY (A) TO MPLX LP, (B) PURSUANT TO A REGISTRATION STATEMENT WHICH HAS BECOME EFFECTIVE UNDER THE SECURITIES ACT, (C) TO A QUALIFIED INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A UNDER THE SECURITIES ACT, (D) IN AN OFFSHORE TRANSACTION IN COMPLIANCE WITH RULE 904 OF REGULATION S UNDER THE SECURITIES ACT, OR (E) PURSUANT TO AN EXEMPTION FROM REGISTRATION PROVIDED BY RULE 144 UNDER THE SECURITIES ACT OR ANY OTHER AVAILABLE EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.

PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (2)(C) ABOVE OR (2)(D) ABOVE, A DULY COMPLETED AND SIGNED CERTIFICATE (THE FORM OF WHICH MAY BE OBTAINED FROM THE TRUSTEE) MUST BE DELIVERED TO THE TRUSTEE. PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (E) ABOVE, MPLX LP RESERVES THE RIGHT TO REQUIRE THE DELIVERY OF SUCH LEGAL OPINIONS, CERTIFICATIONS OR OTHER EVIDENCE AS MAY REASONABLY BE REQUIRED IN ORDER TO DETERMINE THAT THE PROPOSED TRANSFER IS BEING MADE IN COMPLIANCE WITH THE SECURITIES ACT AND APPLICABLE STATE SECURITIES LAWS. NO REPRESENTATION IS MADE AS TO THE AVAILABILITY OF ANY RULE 144 EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.]

MPLX LP, a limited partnership duly formed and existing under the laws of the State of Delaware (herein called the “Partnership,” which term includes any successor Person under the Indenture hereinafter referred to), for value received, hereby promises to pay to [•] [Insert if Global Security: CEDE & CO.], or registered assigns, the principal sum of [•] Dollars ($[•]) [Insert if Global Security: , or such greater or lesser amount as indicated on the Schedule of Increases or Decreases in the Principal Amount of Securities attached hereto,] on October 15, 2022, and to pay interest thereon from April 15, 2019 or from the most recent Interest Payment Date to which interest has been paid or duly provided for, semi-annually on April 15 and October 15 in each year commencing October 15, 2019, at the rate of 6.250% per annum, until the principal hereof is paid or made available for payment. Interest on the Notes will be paid on the basis of a 360-day year consisting of twelve 30-day months. The Partnership shall pay Additional Interest, if any, on the applicable Interest Payment Date in the same manner as interest is paid on the Notes and in the amounts set forth in the Registration Rights Agreement. The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date will, as provided in such Indenture, be paid to the Person in whose name this Debt Security (or one or more Predecessor Securities) is registered at the close of business on the Regular Record Date for such interest, which shall be April 1 or October 1 (whether or not a Business Day), as the case may be, next preceding such Interest Payment Date. Any such interest not so punctually paid or duly provided for will forthwith cease to be payable to the Holder on such Regular Record Date and may either be paid to the Person in whose

name this Debt Security (or one or more Predecessor Securities) is registered at the close of business on a Special Record Date for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Debt Securities of this series not less than 10 days prior to such Special Record Date, or be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange on which the Debt Securities of this series may be listed, and upon such notice as may be required by such exchange all as more fully provided in said Indenture. If an Interest Payment Date, a Stated Maturity or a Redemption Date with respect to this Debt Security falls on a day that is not a Business Day, the payment will be made on the next Business Day and no interest will accrue for the period from and after such Interest Payment Date, Stated Maturity or Redemption Date.

Payment of the principal of (and premium, if any) and interest on this Debt Security will be made at the office or agency of the Partnership maintained for that purpose in New York, New York, in such coin or currency of the United States of America as at the time of payment is legal tender for payment of public and private debts; provided, however, that (1) payments on any Global Security shall be made by electronic (same-day) funds transfer to the Depositary and (2) at the option of the Partnership payment of interest may be made by check mailed to the address of the Person entitled thereto as such address shall appear in the Debt Security Register or by electronic funds transfer to an account maintained by the Person entitled thereto as specified in the Debt Security Register, provided that such Person shall have given the Trustee written instructions.

Reference is hereby made to the further provisions of this Debt Security set forth on the reverse hereof, which further provisions shall for all purposes have the same effect as if set forth at this place.

Unless the certificate of authentication hereon has been executed by the Trustee referred to on the reverse hereof by manual signature, this Debt Security shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose.

IN WITNESS WHEREOF, the Partnership has caused this instrument to be duly executed.

Dated:

CERTIFICATE OF AUTHENTICATION

This is one of the Debt Securities of the series designated therein referred to in the within-mentioned Indenture.

Dated:

MPLX LP

6.250% Senior Notes due 2022

This Security is one of a duly authorized issue of Debt Securities of the Partnership (herein called the “Securities”), issued and to be issued in one or more series under a Senior Indenture, dated as of February 12, 2015, as amended or supplemented to date, including as amended and supplemented by the Seventeenth Supplemental Indenture, dated as of September 23, 2019 (herein called the “Indenture,” which term shall have the meaning assigned to it in such instrument), between the Partnership and The Bank of New York Mellon Trust Company, N.A., as Trustee (herein called the “Trustee,” which term includes any successor trustee under the Indenture), and reference is hereby made to the Indenture for a statement of the respective rights, limitations of rights, duties and immunities thereunder of the Partnership, the Trustee and the Holders of the Securities and of the terms upon which the Securities are, and are to be, authenticated and delivered. This Security is one of the series designated on the face hereof initially limited in aggregate principal amount to $[•].

The Securities are subject to redemption, in whole at any time or in part from time to time, at the election of the Partnership, prior to their maturity date, at the redemption prices (expressed as percentages of the principal amount of such Securities to be redeemed) set forth below, plus accrued and unpaid interest on the principal amount being redeemed to, but not including, the Redemption Date, subject to the right of Holders of record on the relevant record date to receive interest due on the relevant Interest Payment Date, if redeemed during the twelve-month period beginning on October 15 of each of the years indicated below:

Notice of the redemption will be transmitted to holders of Securities at least 15 and not more than 60 days prior to the Redemption Date. If fewer than all of the Securities are to be redeemed, the Trustee will select the particular Securities or portions thereof for redemption from the outstanding Securities not previously called by any of the following methods: (i) in compliance with the requirements of the principal national securities exchange, if any, on which such Securities are listed, (2) on a pro rata basis to the extent practicable and in accordance with the procedures of the Depositary or (3) by lot or in such other similar method in accordance with the procedures of the depositary of such Securities.

Unless the Partnership defaults in payment of the redemption price, on or after the Redemption Date, interest will cease to accrue on the Securities or portions thereof called for redemption.

In the event of redemption of this Security in part only, a new Security or Securities of this series and of like tenor for the unredeemed portion hereof will be issued in the name of the Holder hereof upon the cancellation hereof.

The Indenture contains provisions for defeasance at any time of the entire indebtedness of this Security or of certain restrictive covenants and Events of Default with respect to this Security, in each case upon compliance with certain conditions set forth in the Indenture.

The Indenture contains provisions permitting the Partnership and the Trustee to modify the Indenture or any supplemental indenture without the consent of the Holders for one or more of the following purposes: (1) to evidence the succession of another Person to the Partnership; (2) to surrender any right or power conferred by the Indenture, to add to the covenants for the protection of the Holders of the Securities or to add additional defaults or events of default; (3) to cure any ambiguity, to correct or supplement any provision of the Indenture which may be defective or inconsistent with any other provision of the Indenture, or to make any other provisions with respect to matters or questions arising under the Indenture as shall not adversely affect the interests of the Holders; (4) to permit qualification of the Indenture or any supplemental indenture under the TIA; (5) to permit or facilitate the issuance of Debt Securities of any series in uncertificated form; (6) to secure any or all Debt Securities; (7) to make any change that does not adversely affect the rights of any Holder; (8) to add to, change or eliminate any of the provisions of the Indenture in respect of one or more Debt Securities, under certain conditions specified therein; (9) to evidence and provide acceptance of appointment thereunder by a successor or separate Trustee and to add to or change the provisions under the Indenture as necessary; and (10) to establish the form or terms of Debt Securities of a particular series as permitted by Sections 2.01 and 2.03 of the Indenture.

The Indenture also permits, with certain exceptions as therein provided, the amendment thereof and the modification of the rights and obligations of the Partnership and the rights of the Holders of the Securities of each series to be affected under the Indenture at any time by the Partnership and the Trustee with the consent of the Holders of not less than a majority in aggregate principal amount of the Securities at the time Outstanding of each series to be affected. The Indenture also contains provisions permitting the Holders of at least a majority in aggregate principal amount of the Securities at the time Outstanding, on behalf of the Holders of all Securities, to waive compliance by the Partnership with certain provisions of the Indenture and certain past defaults under the Indenture and their consequences. Any such consent or waiver by the Holder of this Security shall be conclusive and binding upon such Holder and upon all future Holders of this Security and of any Security issued upon the registration of transfer hereof or in exchange herefor or in lieu hereof, whether or not notation of such consent or waiver is made upon this Security.

As provided in and subject to the provisions of the Indenture, the Holder of this Security shall not have the right to institute any proceeding with respect to the Indenture or for the appointment of a receiver or trustee or for any other remedy thereunder, unless such Holder shall have previously given the Trustee written notice of a continuing Event

of Default with respect to the Securities, the Holders of not less than 25% in aggregate principal amount of the Securities then Outstanding shall have made written request to the Trustee to institute proceedings in respect of such Event of Default as Trustee and offered the Trustee indemnity, and the Trustee shall not have received from the Holders of a majority in principal amount of the Securities then Outstanding a direction inconsistent with such request, and shall have failed to institute any such proceeding, for 60 days after receipt of such notice, request and offer of indemnity. The foregoing shall not apply to any suit instituted by the Holder of this Security for the enforcement of any payment of principal hereof or any premium or interest hereon on or after the respective due dates expressed herein.

No reference herein to the Indenture and no provision of this Security or of the Indenture shall alter or impair the obligation of the Partnership, which is absolute and unconditional, to pay the principal of and any premium and interest on this Security at the times, place and rate, and in the coin or currency, herein prescribed.

As provided in the Indenture and subject to certain limitations therein set forth, the transfer of this Security is registrable in the Debt Security Register, upon surrender of this Security for registration of transfer at the office or agency of the Partnership in any place where the principal of and any premium and interest on this Security are payable, duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Partnership and the Registrar duly executed by, the Holder hereof or his attorney duly authorized in writing, and thereupon one or more new Securities and of like tenor, of authorized denominations and for the same aggregate principal amount, will be issued to the designated transferee or transferees.

The Securities are issuable only in registered form without coupons in denominations of $2,000 and integral multiples of $1,000 in excess thereof. As provided in the Indenture and subject to certain limitations therein set forth, the Securities are exchangeable for a like aggregate principal amount of Securities and of like tenor of a different authorized denomination, as requested by the Holder surrendering the same.

No service charge shall be made for any such registration of transfer or exchange, but, subject to any applicable provisions of the Indenture, the Partnership may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection therewith.

Prior to due presentment of this Security for registration of transfer, the Partnership, the Trustee and any agent of the Partnership or the Trustee may treat the Person in whose name this Security is registered as the owner hereof for all purposes, whether or not this Security be overdue, and neither the Partnership, the Trustee nor any such agent shall be affected by notice to the contrary.

All terms used in this Security which are defined in the Indenture shall have the meaning assigned to them in the Indenture.

FORM OF ASSIGNMENT

ABBREVIATIONS

Customary abbreviations may be used in the name of a Securityholder or an assignee, such as TEN COM (=tenants in common), TEN ENT (=tenants by the entireties), JT TEN (=joint tenants with rights of survivorship and not as tenants in common), CUST (=custodian), and U/G/M/A (=Uniform Gift to Minors Act).

Additional abbreviations may also be used though not in the above list.

FOR VALUE RECEIVED, the undersigned hereby sell(s),

assign(s) and transfer(s) unto

Please insert Social Security or

other identifying number of assignee

PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING POSTAL ZIP CODE, OF ASSIGNEE

the within Security and all rights thereunder, hereby irrevocably constituting and appointing                                               attorney to transfer said Security on the books of the Partnership, with full power of substitution in the premises.

EXHIBIT B

FORM OF CERTIFICATE TO BE DELIVERED UPON EXCHANGE OR REGISTRATION OF TRANSFER OF NOTES

Re: 6.250% Senior Notes due 2022 (the “Notes”) of MPLX LP (the “Partnership”)

This Certificate relates to $                     principal amount of Notes held in book-entry or definitive form by (the “Transferor”). The Transferor has requested the Registrar by written order to exchange or register the transfer of a Note or Notes or beneficial interests therein (the “Transfer”).

In connection with such request and in respect of each such Note or beneficial interest therein, the Transferor does hereby certify that the Transferor is familiar with the Indenture relating to the above-captioned Notes and that the Transfer does not require registration under the Securities Act of 1933, as amended (the “Securities Act”), because:

Fill in blank or check appropriate item, as applicable.

EXHIBIT C

FORM OF CERTIFICATE TO BE DELIVERED IN CONNECTION WITH TRANSFERS

PURSUANT TO REGULATION S

Re: 6.250% Senior Notes due 2022 (the “Notes”) of MPLX LP (the “Partnership”)

This Certificate relates to $                      principal amount of Notes held in book-entry form by (the “Transferor”).

The Transferor has requested the Registrar by written order to exchange or register the transfer of a Note or Notes or beneficial interests therein (the “Transfer”) for an interest in the Regulation S Temporary Global Note to be held with [Euroclear] [Clearstream] through the Depositary (in each case as defined in the Indenture related to the above-referenced Notes).

In connection with such request and in respect of each such Note or beneficial interest therein, the Transferor does hereby certify that the Transferor is familiar with such Indenture and Establishment Action and that:

(a) the offer of such Notes or beneficial interests was not made to a person in the United States or for the benefit of a person in the United States (other than an Initial Purchaser);

(b) at the time the buy order was originated, the transferee was outside the United States or the Transferor and any person acting on its behalf reasonably believed that the transferee was outside the United States; or the transaction was executed in, on or through the facilities of a designated offshore securities market and neither the Transferor nor any person acting on its behalf knows that the transaction was prearranged with a buyer in the United States;

(c) no directed selling efforts have been made by the Transferor in the United States in contravention of the requirements of Rule 903(a) or Rule 904(a) of Regulation S under the U.S. Securities Act of 1933, as amended (the “Securities Act”), as applicable;

(d) the transaction is not part of a plan or scheme to evade the registration requirements of the Securities Act; and

(e) if the proposed transfer is being made prior to the expiration of a 40-day “distribution compliance period” as defined in Regulation S under the Securities Act, the transfer is being made (a) to a person that is not a U.S. person or for the account or benefit of a person that is not a U.S. person within the meaning of Regulation S under the Securities Act; or (b) to a “qualified institutional buyer” within the meaning of Rule 144A under the Securities Act, in each case that holds such Note or beneficial interests through [Euroclear] [Clearstream].

EXHIBIT 4.2

EIGHTEENTH SUPPLEMENTAL INDENTURE

THIS EIGHTEENTH SUPPLEMENTAL INDENTURE, dated as of September 23, 2019 (this “Supplemental Indenture”), is between MPLX LP, a limited partnership duly formed and existing under the laws of the State of Delaware (the “Partnership”), and The Bank of New York Mellon Trust Company, N.A., a national banking association, as trustee (the “Trustee”).

WITNESSETH

WHEREAS, pursuant to the Senior Indenture, dated as of February 12, 2015 (the “Base Indenture”), as supplemented by the First Supplemental Indenture, dated as of February 12, 2015, the Second Supplemental Indenture, dated as of December 22, 2015, the Third Supplemental Indenture, dated as of December 22, 2015, the Fourth Supplemental Indenture, dated as of December 22, 2015, the Fifth Supplemental Indenture, dated as of December 22, 2015, the Sixth Supplemental Indenture, dated as of February 10, 2017, the Seventh Supplemental Indenture, dated as of February 10, 2017, the Eighth Supplemental Indenture, dated as of February 8, 2018, the Ninth Supplemental Indenture, dated as of February 8, 2018, the Tenth Supplemental Indenture, dated as of February 8, 2018, the Eleventh Supplemental Indenture, dated as of February 8, 2018, the Twelfth Supplemental Indenture, dated as of February 8, 2018, the Thirteenth Supplemental Indenture, dated as of November 15, 2018, the Fourteenth Supplemental Indenture, dated as of November 15, 2018, the Fifteenth Supplemental Indenture, dated as of September 9, 2019, the Sixteenth Supplemental Indenture, dated as of September 9, 2019, and the Seventeenth Supplemental Indenture, dated as of September 23, 2019 (as so supplemented, the “Indenture”), in each case between the Partnership and the Trustee, the Partnership may from time to time issue and sell Debt Securities in one or more series;

WHEREAS, the Partnership desires to create and authorize a new series of Debt Securities entitled “3.500% Senior Notes due 2022” (the “Notes”), limited initially to $486,302,000 in aggregate principal amount, and to provide the terms and conditions upon which the Notes are to be executed, registered, authenticated, issued and delivered, the Partnership has duly authorized the execution and delivery of this Supplemental Indenture;

WHEREAS, the Notes are a series of Debt Securities and are being issued under the Indenture, as supplemented by this Supplemental Indenture, and are subject to the terms contained therein and herein;

WHEREAS, the Notes are to be substantially in the form attached hereto as Exhibit A; and

WHEREAS, all acts and things necessary to make the Notes, when executed by the Partnership and authenticated and delivered by or on behalf of the Trustee as provided in the Indenture and this Supplemental Indenture, the valid, binding and legal obligations of the Partnership, and to make this Supplemental Indenture a legal, binding and enforceable agreement, have been done and performed.

NOW, THEREFORE, in order to declare the terms and conditions upon which the Notes are executed, registered, authenticated, issued and delivered, and in consideration of the foregoing premises and the purchase of such Notes by the Holders thereof, the Partnership and the Trustee mutually covenant and agree, for the equal and proportionate benefit of the Holders from time to time of the Notes, as follows:

Section 1. Definitions. Terms used in this Supplemental Indenture and not defined herein shall have the respective meanings given such terms in the Indenture.

Section 2. Other Definitions. In addition, the following terms shall have the following meanings with respect to the Notes:

“Additional Interest” means “Additional Interest” payable pursuant to the Registration Rights Agreement.

“Board Resolution” means a copy of a resolution or resolutions of the Board of Directors, certified by the Secretary or an Assistant Secretary of the General Partner to be in full force and effect on the date of such certification, and delivered to the Trustee.

“Clearstream” means Clearstream Banking, société anonyme, or any successor securities clearing agency.

“Consolidated Net Tangible Assets” means the aggregate value of all assets of the Partnership and its Subsidiaries after deducting therefrom: (i) all current liabilities, excluding all short-term indebtedness and the current portion of long-term indebtedness; (ii) all investments in unconsolidated subsidiaries and all investments accounted for on the equity basis; and (iii) all goodwill patents and trademarks, unamortized debt discounts and other similar intangibles (all determined in conformity with generally accepted accounting principles and calculated on a basis consistent with the Partnership’s most recent audited consolidated financial statements).

“Euroclear” means Euroclear Bank S.A./N.V., as operator of Euroclear systems Clearance System or any successor securities clearing agency.

“Exchange Global Notes” has the meaning set forth in Section 7(a) herein.

“Exchange Notes” means any notes issued in exchange for Notes pursuant to the Registration Rights Agreement or similar agreement.

“Global Notes” has the meaning set forth in Section 7(c) herein.

“Interest Payment Date,” when used with respect to any installment of interest on any Debt Security, means the date specified in such Debt Security as the fixed date on which such installment of interest is due and payable.

“Mortgage” means as the context may require, (i) to mortgage, pledge, encumber or subject to a lien or (ii) a mortgage, pledge, encumbrance or lien.

2

“Predecessor Security” of any particular Debt Security means every previous Debt Security evidencing all or a portion of the same debt as that evidenced by such particular Debt Security; and, for the purposes of this definition, any Debt Security authenticated and delivered under Section 2.09 of the Base Indenture in exchange for or in lieu of a mutilated, destroyed, lost or stolen Debt Security shall be deemed to evidence the same debt as the mutilated, destroyed, lost or stolen Debt Security.

“QIB” means a “qualified institutional buyer” as defined in Rule 144A.

“Registration Rights Agreement” means the registration rights agreement, dated as of the date of this Supplemental Indenture, by and among the Partnership, the General Partner, Barclays Capital Inc., MUFG Securities Americas Inc. and Wells Fargo Securities, LLC.

“Regular Record Date” for the interest payable on any Interest Payment Date on the Debt Securities means the date specified for that purpose as contemplated by Section 2.03 of the Base Indenture.

“Regulation S” means Regulation S promulgated under the Securities Act.

“Regulation S Global Notes” has the meaning set forth in Section 7(c) herein.

“Regulation S Notes” has the meaning set forth in Section 7(c) herein.

“Restricted Notes Legend” has the meaning set forth in Section 7(d) herein.

“Restricted Period” has the meaning set forth in Section 7(c) herein.

“Rule 144” means Rule 144 promulgated under the Securities Act.

“Rule 144A” means Rule 144A promulgated under the Securities Act.

“Rule 144A Global Notes” has the meaning set forth in Section 7(b) herein.

“Rule 144A Notes” has the meaning set forth in Section 7(b) herein.

“Special Record Date” for the payment of any Defaulted Interest means a date fixed by the Trustee pursuant to Section 2.17 of the Base Indenture.

“Transfer Restricted Note” means any Note that bears or is required to bear the Restricted Notes Legend.

“U.S. person” means a “U.S. person” as defined in Regulation S.

3

Section 3. Creation and Authorization of Series.

(a) There is hereby created and authorized the following new series of Debt Securities to be issued under the Indenture, to be designated as the “3.500% Senior Notes due 2022.”

(b) The Notes shall be limited initially to $486,302,000 in aggregate principal amount. Notwithstanding the foregoing initial aggregate principal amount, the Partnership may, from time to time, without notice to or consent of the Holders of the Notes, increase the principal amount of the Notes that may be issued under this Supplemental Indenture and issue such increased principal amount (or any portion thereof), in which case any additional Notes so issued will have the same terms and conditions other than the public offering price, original interest accrual date and initial interest payment date, and the same CUSIP numbers as the applicable series of Notes previously issued, will be fungible with the applicable series of Notes previously issued for U.S. federal income tax purposes, and will carry the same right to receive accrued and unpaid interest as the Notes previously issued, and such additional notes will form a single series with the Notes of such series previously issued, including, without limitation, for purposes of waivers, amendments, redemptions and, if any, offers to purchase, and will rank equally and ratably with the Notes of such series previously issued.

(c) The date on which the principal is payable on the Notes, unless accelerated pursuant to the Indenture, shall be as provided in the form of security attached hereto as Exhibit A.

(d) The Notes shall bear interest as provided in the form of security attached hereto as Exhibit A. The Interest Payment Dates and the Regular Record Dates for the determination of Holders of the Notes to whom such interest is payable shall be as provided in the form of security attached hereto as Exhibit A. Additional Interest, if any, will be payable in arrears on each Interest Payment Date following accrual in the same manner as regular interest on the Notes.

(e) The Notes shall be redeemable at the option of the Partnership as set forth in the form of security attached hereto as Exhibit A.

(f) The provisions of Sections 3.04 and 3.05 of the Base Indenture shall not be applicable to the Notes.

(g) The Notes will be issued only in fully registered form, without coupons, in denominations provided herein and in the form of security attached hereto as Exhibit A.

(h) The Events of Default and covenants specified in the Indenture will apply to the Notes.

(i) The defeasance and covenant defeasance provisions of Article XI of the Indenture, including both Sections 11.02 and 11.03 of the Base Indenture, will apply to the Notes.

(j) The Notes shall be issued in the form of one or more Global Securities substantially in the form of security attached hereto as Exhibit A. The Partnership initially appoints The Depository Trust Company to act as Depositary with respect to the Notes. Additional provisions applicable to the Notes issued in the form of a Global Security are set forth in the form of security attached hereto as Exhibit A.

4

(k) The Notes shall be issuable only in denominations of $2,000 and integral multiples of $1,000 in excess thereof.

(l) The Trustee will initially act as the Registrar for the Notes and as the paying agent with respect to the Notes. The Place of Payment will be The Bank of New York Mellon Trust Company, N.A., 240 Greenwich Street, New York, New York 10286.

(m) Except as otherwise set forth herein and in the Notes, the terms of the Notes shall be as set forth in the Indenture, including those made part of the Indenture by reference to the TIA.

Section 4. Additional Covenants. In addition to the covenants set forth in Article IV of the Indenture, the following additional covenants shall apply with respect to the Notes:

Section 4.10 Mortgage of Certain Property.

If the Partnership or any Subsidiary of the Partnership shall Mortgage as security for any indebtedness for money borrowed any pipeline, terminal or other logistics or storage property or asset employed in the transportation, distribution, storage, terminalling, processing or marketing of crude oil, natural gas, condensate or refined products that (i) is located in the United States and (ii) is determined to be a principal property by the Board of Directors in its discretion, the Partnership will secure, or will cause such Subsidiary to secure, the Notes and all other Debt Securities equally and ratably with all indebtedness or obligations secured by the Mortgage then being given; provided, however, that this covenant shall not apply in the case of:

5

Notwithstanding the foregoing restriction contained in this Section 4.10, the Partnership may and may permit its Subsidiaries to incur liens or grant Mortgages on property covered by the restriction above so long as the net book value of the property so encumbered, together with all property subject to the restriction on sale and leasebacks contained in Section 4.11, does not, at the time such lien or Mortgage is granted, exceed fifteen percent (15%) of Consolidated Net Tangible Assets.

Section 4.11 Sale and Leaseback of Certain Properties.

The Partnership will not, nor will it permit any Subsidiary of the Partnership to, sell or transfer any pipeline, terminal or other logistics or storage property or asset employed in the transportation, distribution, storage, terminalling, processing or marketing of crude oil, natural gas, condensate or refined products that (i) is located in the United States and (ii) is determined to be a principal property by the Board of Directors in its discretion, with the intention of taking back a lease of such property; provided, however, this covenant shall not apply if:

6

In the event of such a sale or transfer, the Partnership shall deliver to the Trustee the Board Resolution referred to in the parenthetical phrase contained in subclause (4)(B) of this Section 4.11 and an Officer’s Certificate setting forth all material facts under this Section 4.11.

For the purposes of this Section 4.11, the term retirement of such funded debt shall include the “in substance defeasance” of such funded debt in accordance with then applicable accounting rules.

Section 5. Consolidation, Merger, Sale or Conveyance. With respect to the Notes, Section 10.01 of the Base Indenture shall be amended to include the following language at the end of such section:

For purposes of this Section 10.01, “substantially all of its assets” shall mean, at any date, a portion of the non-current assets reflected in the Partnership’s consolidated balance sheet as of the end of the most recent quarterly period that represents at least sixty-six and two-thirds percent (66 2/3%) of the total reported value of such assets.

7

Section 6. Transfer Restrictions.

(a) The initial offering and sale of the Notes shall not be registered under the Securities Act or any state securities laws. The Notes shall be offered pursuant to exemptions from the registration requirements of the Securities Act in reliance upon Rule 144A and Regulation S promulgated under the Securities Act. For so long as any of the Notes constitute “restricted securities” within the meaning of Rule 144(a)(3) promulgated under the Securities Act, the Partnership shall, if the Partnership is not then subject to the reporting requirements of Section 13 or 15(d) of the Exchange Act, furnish to any Holder or beneficial owner of such Notes, or to any prospective purchaser of such Notes designated by such Holder or beneficial owner, in each case upon the written request of such Holder, beneficial owner or prospective purchaser, the information required to be provided pursuant to Rule 144A(d)(4) promulgated under the Securities Act.

(b) The following provisions shall apply with respect to any proposed transfer of any Transfer Restricted Note prior to the expiration of the holding period applicable to sales of such Notes under Rule 144, and the Registrar shall refuse to register any transfer of such Notes not complying with the restrictions set forth in the Restricted Notes Legend and in this Section 6. In addition to the requirements set forth in Section 2.07 of the Base Indenture, Transfer Restricted Notes that are presented or surrendered for registration of transfer or exchange pursuant to Section 2.07 of the Base Indenture shall be accompanied by the following additional information and documents, as applicable, upon which the Registrar may conclusively rely:

(i) if such Transfer Restricted Notes are being delivered to the Registrar by a Holder for registration in the name of such Holder, without transfer, a certification from such Holder to that effect (in substantially the form of Exhibit B hereto);

(ii) if such Transfer Restricted Notes are being transferred (1) to a QIB in accordance with Rule 144A or (2) pursuant to an effective registration statement under the Securities Act, a certification to that effect from such Holder (in substantially the form of Exhibit B hereto);

(iii) if such Transfer Restricted Notes are being transferred pursuant to an exemption from registration in accordance with Rule 903 or Rule 904 of Regulation S, certifications to that effect from such Holder (in substantially the form of Exhibit B and Exhibit C hereto) and an opinion of counsel to that effect if the Partnership or the Trustee so requests; or

(iv) if such Transfer Restricted Notes are being transferred in reliance on and in compliance with (1) an exemption from registration in accordance with Rule 144 under the Securities Act or (2) another exemption from the registration requirements of the Securities Act, a certification to that effect from such Holder (in substantially the form of Exhibit B attached hereto) and an opinion of counsel, certification or other evidence as may reasonably be required to that effect if the Partnership or the Trustee so requests.

8

(c) A Holder of a beneficial interest in a Regulation S Global Note who wishes to transfer its interest in such Note to a QIB in accordance with Rule 144A who takes delivery in the form of a beneficial interest in the Rule 144A Global Note shall deliver to the Registrar a certification to that effect (in substantially the form of Exhibit B attached hereto) upon which the Registrar may conclusively rely. After the expiration of the Restricted Period, interests in the Regulation S Global Note may be transferred without requiring the certification set forth in this Section 6(c).

(d) The transfer and exchange of Global Notes or beneficial interests therein shall be effected through the Depositary, in accordance with Section 2.07 of the Base Indenture and Section 6 and Section 7 hereof (including the restrictions on transfer set forth therein and herein) and the rules and procedures of the Depositary therefor, which shall include restrictions on transfer comparable to those set forth therein and herein to the extent required by the Securities Act; provided, however, that prior to the expiration of the Restricted Period, transfers and exchanges of beneficial interests in the Regulation S Global Note may be made pursuant to such restrictions only (1) to a Person that is not a U.S. person or for the account or benefit of a Person that is not a U.S. person within the meaning of Regulation S under the Securities Act or (2) to a QIB, in each case that hold such interests through Euroclear or Clearstream.

(e) If Notes are issued upon the registration of transfer, exchange or replacement of Notes not bearing the Restricted Notes Legend, the Notes so issued shall not bear such legend. If Notes are issued upon the registration or transfer, exchange or replacement of Notes bearing the Restricted Notes Legend, or if a request is made to remove the Restricted Notes Legend on a Note, the Notes so issued shall bear the Restricted Notes Legend, or the Restricted Notes Legend shall not be removed, as the case may be, unless there is delivered to the Partnership such satisfactory evidence, which may include an opinion of counsel of recognized standing licensed to practice law in the State of New York and experienced in matters involving the Securities Act, as may be reasonably required by the Partnership that neither the Restricted Notes Legend nor the restrictions on transfer set forth therein are required to ensure that transfers thereof comply with the provisions of Rule 144A, Rule 144 or Regulation S, that such Notes are not “restricted securities” within the meaning of Rule 144 or that such Notes were transferred pursuant to an effective registration statement under the Securities Act. Upon provision of such satisfactory evidence, the Trustee, at the direction of the Partnership, shall authenticate and deliver a Note that does not bear the Restricted Notes Legend. If a Restricted Notes Legend is removed from the face of a Note and the Note is subsequently held by an Affiliate of the Partnership, the Restricted Notes Legend shall be reinstated.

(f) Neither the Trustee nor the Registrar shall have any obligation or duty to monitor, determine or inquire as to compliance with any restrictions on transfer imposed under this Supplemental Indenture or under applicable law with respect to any transfer of any interest in any Note (including any transfers between or among Depositary participants or beneficial owners of interests in any Global Note) other than to require delivery of such certificates and other documentation or evidence as are expressly required by, and to do so only if and when expressly required by the terms of, this Supplemental Indenture, and to examine the same to determine substantial compliance as to form with the express requirements hereof. Notwithstanding anything herein to the contrary, neither the Trustee nor the Registrar shall have any responsibility to receive any letters, opinions or certifications, nor any responsibility to monitor compliance with any transfer restrictions, in connection with any transfer or exchange of any beneficial interest in a Global Note for a beneficial interest in the same Global Note.

9

(g) Notwithstanding the foregoing, in the event that any Transfer Restricted Notes are exchanged for Exchange Notes in connection with an effective registration statement pursuant to the Registration Rights Agreement, the Partnership shall issue and, at the direction of the Partnership, the Trustee shall authenticate the Exchange Notes in exchange for Transfer Restricted Notes accepted for exchange in the exchange offer, which Exchange Notes shall not bear the Restricted Notes Legend, and the Registrar shall rescind any restriction on the transfer of such Exchange Notes.

Section 7. Form of Notes/Legends.

(a) The Notes are being offered only to (A) Persons reasonably believed to be QIBs in reliance on Rule 144A and (B) non-U.S. persons in reliance on Regulation S. Such Notes may thereafter be transferred to, among others, QIBs, and purchasers in reliance on Regulation S, in each case, in accordance with the procedures described herein. Exchange Notes exchanged for interests in the Rule 144A Notes and the Regulation S Notes will be issued in the form of permanent global notes deposited with the Trustee as hereinafter provided, including the appropriate legend set forth in the form of security attached as Exhibit A (the “Exchange Global Notes”). The Exchange Global Notes will be deposited upon issuance with, or on behalf of, the Trustee as custodian for the Depositary, duly executed by the Partnership and authenticated by the Trustee as hereinafter provided. The Exchange Global Notes may be represented by more than one certificate, if so required by the Depositary’s rules regarding the maximum principal amount to be represented by a single certificate.

(b) The Notes offered to QIBs in the United States of America in reliance on Rule 144A (the “Rule 144A Notes”) shall be issued in the form of a permanent global note including appropriate legends as set forth in the form of security attached as Exhibit A (the “Rule 144A Global Notes”), deposited with the Trustee, as custodian for the Depositary, duly executed by the Partnership and authenticated by the Trustee as hereinafter provided. The Rule 144A Global Notes may be represented by more than one certificate, if so required by the Depositary’s rules regarding the maximum principal amount to be represented by a single certificate. The aggregate principal amount of the Rule 144A Global Notes may from time to time be increased or decreased by adjustments made on the records of the Trustee, as custodian for the Depositary, or its nominee, as hereinafter provided.

(c) The Notes offered to non-U.S. persons outside the United States of America (the “Regulation S Notes”) in reliance on Regulation S shall be issued in the form of a permanent global note including appropriate legends as set forth in the form of security attached as Exhibit A (the “Regulation S Global Notes” and, together with the Rule 144A Global Notes and the Exchange Global Notes, the “Global Notes”). Each Regulation S Global Note will be deposited upon issuance with, or on behalf of, the Trustee as custodian for the Depositary. Prior to the 40th day after the date the Notes are issued (such period through and including such 40th day, the “Restricted Period”), interests in the Regulation S Global Notes may only be transferred to non-U.S. persons pursuant to Regulation S, unless exchanged for interests in a Global Note in

10

accordance with the transfer and certification requirements described herein. Investors may hold their interests in the Regulation S Global Note through organizations other than Euroclear or Clearstream that are participants in the Depositary’s system or directly through Euroclear or Clearstream, if they are participants in such systems, or indirectly through organizations which are participants in such systems. If such interests are held through Euroclear or Clearstream, Euroclear and Clearstream will hold such interests in the applicable Regulation S Global Note on behalf of their participants through customers’ securities accounts in their respective names on the books of their respective depositaries. Such depositaries, in turn, will hold such interests in the applicable Regulation S Global Note in customers’ securities accounts in the depositaries’ names on the books of the Depositary. The Regulation S Global Notes may be represented by more than one certificate, if so required by the Depositary’s rules regarding the maximum principal amount to be represented by a single certificate. The aggregate principal amount of the Regulation S Global Notes may from time to time be increased or decreased by adjustments made on the records of the Trustee, as custodian for the Depositary or its nominee, as hereinafter provided.

(d) Unless and until (i) a Note issued as a Transfer Restricted Note is sold under an effective registration statement, (ii) a Note issued as a Transfer Restricted Note is exchanged for an Exchange Note in connection with an effective registration statement pursuant to the Registration Rights Agreement or (iii) the Partnership receives an opinion of counsel satisfactory to it to the effect that neither such legend nor the related restrictions on transfer are required in order to maintain compliance with the provisions of the Securities Act:

(1) each Transfer Restricted Note shall bear the following legend on the face thereof (the “Restricted Notes Legend”):

THIS NOTE HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”), AND MAY NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED EXCEPT IN ACCORDANCE WITH THE FOLLOWING SENTENCE. BY ITS ACQUISITION HEREOF OR OF A BENEFICIAL INTEREST HEREIN, THE ACQUIRER (1) REPRESENTS THAT (A) IT AND ANY ACCOUNT FOR WHICH IT IS ACTING IS A “QUALIFIED INSTITUTIONAL BUYER” (WITHIN THE MEANING OF RULE 144A UNDER THE SECURITIES ACT) AND THAT IT EXERCISES SOLE INVESTMENT DISCRETION WITH RESPECT TO EACH SUCH ACCOUNT, OR (B) IT IS NOT A “U.S. PERSON” (WITHIN THE MEANING OF REGULATION S UNDER THE SECURITIES ACT) AND (2) AGREES FOR THE BENEFIT OF MPLX LP THAT IT WILL NOT OFFER, SELL, PLEDGE OR OTHERWISE TRANSFER THIS NOTE OR ANY BENEFICIAL INTEREST HEREIN, EXCEPT IN ACCORDANCE WITH THE SECURITIES ACT AND ANY APPLICABLE SECURITIES LAWS OF ANY STATE OF THE UNITED STATES AND ONLY (A) TO MPLX LP, (B) PURSUANT TO A REGISTRATION STATEMENT WHICH HAS BECOME EFFECTIVE UNDER THE SECURITIES ACT, (C) TO A QUALIFIED INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A UNDER THE SECURITIES ACT, (D) IN AN OFFSHORE TRANSACTION IN COMPLIANCE WITH RULE 904 OF REGULATION S UNDER THE SECURITIES ACT, OR (E) PURSUANT TO AN EXEMPTION FROM REGISTRATION PROVIDED BY RULE 144 UNDER THE SECURITIES ACT OR ANY OTHER AVAILABLE EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.

11

PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (2)(C) ABOVE OR (2)(D) ABOVE, A DULY COMPLETED AND SIGNED CERTIFICATE (THE FORM OF WHICH MAY BE OBTAINED FROM THE TRUSTEE) MUST BE DELIVERED TO THE TRUSTEE. PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (E) ABOVE, MPLX LP RESERVES THE RIGHT TO REQUIRE THE DELIVERY OF SUCH LEGAL OPINIONS, CERTIFICATIONS OR OTHER EVIDENCE AS MAY REASONABLY BE REQUIRED IN ORDER TO DETERMINE THAT THE PROPOSED TRANSFER IS BEING MADE IN COMPLIANCE WITH THE SECURITIES ACT AND APPLICABLE STATE SECURITIES LAWS. NO REPRESENTATION IS MADE AS TO THE AVAILABILITY OF ANY RULE 144 EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.

(2) each Global Note shall bear the following legend on the face thereof:

UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (“DTC”), NEW YORK, NEW YORK, TO THE PARTNERSHIP OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO., OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

TRANSFERS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS IN WHOLE, BUT NOT IN PART, TO NOMINEES OF DTC OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR’S NOMINEE AND TRANSFERS OF PORTIONS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN THE INDENTURE REFERRED TO HEREIN.

Section 8. Effect of Supplemental Indenture. The provisions of this Supplemental Indenture are intended to supplement those of the Indenture as in effect immediately prior to the execution and delivery hereof. The Indenture shall remain in full force and effect except to the extent that the provisions of the Indenture are expressly modified by the terms of this Supplemental Indenture.

Section 9. Governing Law. This Supplemental Indenture and the Notes shall be governed by and construed in accordance with the law of the State of New York, without giving effect to any principles of conflicts of laws thereunder to the extent the application of the laws of another jurisdiction would be required thereby.

12

Section 10. Trustee Not Responsible for Recitals or Issuance of Notes. The recitals and statements contained herein shall be taken as statements of the Partnership, and the Trustee assumes no responsibility for their correctness. The Trustee makes no representations as to the validity or sufficiency of this Supplemental Indenture or of the Notes other than with respect to the Trustee’s execution of this Supplemental Indenture and authentication of the Notes. The Trustee shall not be accountable for the use or application by the Partnership of the Notes or the proceeds thereof.

Section 11. Conflict with the TIA. If any provision hereof limits, qualifies or conflicts with a provision of the TIA that is required under the TIA to be a part of and govern this Supplemental Indenture, the latter provision shall control. If any provision of this Supplemental Indenture modifies or excludes any provision of the TIA that may be so modified or excluded, the latter provision shall be deemed to apply to this Supplemental Indenture as so modified or to be excluded, as the case may be.

Section 12. Counterparts. This Supplemental Indenture may be executed in any number of counterparts, each of which shall be an original; but such counterparts shall together constitute one and the same instrument. The exchange of copies of this Supplemental Indenture and of signature pages by facsimile or electronic (i.e., “pdf” or “tif”) transmission shall constitute effective execution and delivery of this Supplemental Indenture for all purposes. Signatures of the parties hereto transmitted by facsimile or electronic (i.e., “pdf” or “tif”) transmission shall be deemed to be their original signatures for all purposes of the Supplemental Indenture as to the parties hereto and may be used in lieu of the original.

[The remainder of this page is left blank intentionally]

13

IN WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture to be duly executed as of the day and year first above written.

[Signature Page to Eighteenth Supplemental Indenture]

[Signature Page to Eighteenth Supplemental Indenture]

Exhibit A

MPLX LP

3.500% Senior Notes due 2022

[FOR GLOBAL NOTES: UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (“DTC”), NEW YORK, NEW YORK, TO THE PARTNERSHIP OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO., OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

TRANSFERS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS IN WHOLE, BUT NOT IN PART, TO NOMINEES OF DTC OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR’S NOMINEE AND TRANSFERS OF PORTIONS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN THE INDENTURE REFERRED TO HEREIN.]

[FOR TRANSFER RESTRICTED NOTES: THIS NOTE HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”), AND MAY NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED EXCEPT IN ACCORDANCE WITH THE FOLLOWING SENTENCE. BY ITS ACQUISITION HEREOF OR OF A BENEFICIAL INTEREST HEREIN, THE ACQUIRER (1) REPRESENTS THAT (A) IT AND ANY ACCOUNT FOR WHICH IT IS ACTING IS A “QUALIFIED INSTITUTIONAL BUYER” (WITHIN THE MEANING OF RULE 144A UNDER THE SECURITIES ACT) AND THAT IT EXERCISES SOLE INVESTMENT DISCRETION WITH RESPECT TO EACH SUCH ACCOUNT, OR (B) IT IS NOT A “U.S. PERSON” (WITHIN THE MEANING OF REGULATION S UNDER THE SECURITIES ACT) AND (2) AGREES FOR THE BENEFIT OF MPLX LP THAT IT WILL NOT OFFER, SELL, PLEDGE OR OTHERWISE TRANSFER THIS NOTE OR ANY BENEFICIAL INTEREST HEREIN, EXCEPT IN ACCORDANCE WITH THE SECURITIES ACT

AND ANY APPLICABLE SECURITIES LAWS OF ANY STATE OF THE UNITED STATES AND ONLY (A) TO MPLX LP, (B) PURSUANT TO A REGISTRATION STATEMENT WHICH HAS BECOME EFFECTIVE UNDER THE SECURITIES ACT, (C) TO A QUALIFIED INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A UNDER THE SECURITIES ACT, (D) IN AN OFFSHORE TRANSACTION IN COMPLIANCE WITH RULE 904 OF REGULATION S UNDER THE SECURITIES ACT, OR (E) PURSUANT TO AN EXEMPTION FROM REGISTRATION PROVIDED BY RULE 144 UNDER THE SECURITIES ACT OR ANY OTHER AVAILABLE EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.

PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (2)(C) ABOVE OR (2)(D) ABOVE, A DULY COMPLETED AND SIGNED CERTIFICATE (THE FORM OF WHICH MAY BE OBTAINED FROM THE TRUSTEE) MUST BE DELIVERED TO THE TRUSTEE. PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (E) ABOVE, MPLX LP RESERVES THE RIGHT TO REQUIRE THE DELIVERY OF SUCH LEGAL OPINIONS, CERTIFICATIONS OR OTHER EVIDENCE AS MAY REASONABLY BE REQUIRED IN ORDER TO DETERMINE THAT THE PROPOSED TRANSFER IS BEING MADE IN COMPLIANCE WITH THE SECURITIES ACT AND APPLICABLE STATE SECURITIES LAWS. NO REPRESENTATION IS MADE AS TO THE AVAILABILITY OF ANY RULE 144 EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.]

MPLX LP, a limited partnership duly formed and existing under the laws of the State of Delaware (herein called the “Partnership,” which term includes any successor Person under the Indenture hereinafter referred to), for value received, hereby promises to pay to [•] [Insert if Global Security: CEDE & CO.], or registered assigns, the principal sum of [•] Dollars ($[•]) [Insert if Global Security: , or such greater or lesser amount as indicated on the Schedule of Increases or Decreases in the Principal Amount of Securities attached hereto,] on December 1, 2022, and to pay interest thereon from June 1, 2019 or from the most recent Interest Payment Date to which interest has been paid or duly provided for, semi-annually on June 1 and December 1 in each year commencing December 1, 2019, at the rate of 3.500% per annum, until the principal hereof is paid or made available for payment. Interest on the Notes will be paid on the basis of a 360-day year consisting of twelve 30-day months. The Partnership shall pay Additional Interest, if any, on the applicable Interest Payment Date in the same manner as interest is paid on the Notes and in the amounts set forth in the Registration Rights Agreement. The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date will, as provided in such Indenture, be paid to the Person in whose name this Debt Security (or one or more Predecessor Securities) is registered at the close of business on the Regular Record Date for such interest, which shall be May 15 or November 15 (whether or not a Business Day), as the case may be, next preceding such Interest Payment Date. Any such interest not so punctually paid or duly provided for will forthwith cease to be payable to the Holder on such Regular Record Date and may either be paid to the Person in whose

name this Debt Security (or one or more Predecessor Securities) is registered at the close of business on a Special Record Date for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Debt Securities of this series not less than 10 days prior to such Special Record Date, or be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange on which the Debt Securities of this series may be listed, and upon such notice as may be required by such exchange all as more fully provided in said Indenture. If an Interest Payment Date, a Stated Maturity or a Redemption Date with respect to this Debt Security falls on a day that is not a Business Day, the payment will be made on the next Business Day and no interest will accrue for the period from and after such Interest Payment Date, Stated Maturity or Redemption Date.

Payment of the principal of (and premium, if any) and interest on this Debt Security will be made at the office or agency of the Partnership maintained for that purpose in New York, New York, in such coin or currency of the United States of America as at the time of payment is legal tender for payment of public and private debts; provided, however, that (1) payments on any Global Security shall be made by electronic (same-day) funds transfer to the Depositary and (2) at the option of the Partnership payment of interest may be made by check mailed to the address of the Person entitled thereto as such address shall appear in the Debt Security Register or by electronic funds transfer to an account maintained by the Person entitled thereto as specified in the Debt Security Register, provided that such Person shall have given the Trustee written instructions.

Reference is hereby made to the further provisions of this Debt Security set forth on the reverse hereof, which further provisions shall for all purposes have the same effect as if set forth at this place.

Unless the certificate of authentication hereon has been executed by the Trustee referred to on the reverse hereof by manual signature, this Debt Security shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose.

IN WITNESS WHEREOF, the Partnership has caused this instrument to be duly executed.

Dated:

CERTIFICATE OF AUTHENTICATION

This is one of the Debt Securities of the series designated therein referred to in the within-mentioned Indenture.

Dated:

MPLX LP

3.500% Senior Notes due 2022

This Security is one of a duly authorized issue of Debt Securities of the Partnership (herein called the “Securities”), issued and to be issued in one or more series under a Senior Indenture, dated as of February 12, 2015, as amended or supplemented to date, including as amended and supplemented by the Eighteenth Supplemental Indenture, dated as of September 23, 2019 (herein called the “Indenture,” which term shall have the meaning assigned to it in such instrument), between the Partnership and The Bank of New York Mellon Trust Company, N.A., as Trustee (herein called the “Trustee,” which term includes any successor trustee under the Indenture), and reference is hereby made to the Indenture for a statement of the respective rights, limitations of rights, duties and immunities thereunder of the Partnership, the Trustee and the Holders of the Securities and of the terms upon which the Securities are, and are to be, authenticated and delivered. This Security is one of the series designated on the face hereof initially limited in aggregate principal amount to $[•].

Prior to November 1, 2022, the Securities are subject to redemption, in whole at any time or in part from time to time, at the election of the Partnership, at a redemption price equal to the greater of (1) 100% of the principal amount of such Securities to be redeemed or (2) the sum of the present values of the remaining scheduled payments of principal and interest on the Securities to be redeemed that would be due if such Securities matured on November 1, 2022 (exclusive of interest accrued to the Redemption Date) discounted to the Redemption Date on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the then current Treasury Rate plus 25 basis points, plus, in either case, accrued and unpaid interest on the principal amount being redeemed to, but not including, the Redemption Date.

On or after November 1, 2022, the Securities are subject to redemption, in whole at any time or in part from time to time, at the election of the Partnership, at a redemption price equal to 100% of the principal amount of such Securities to be redeemed plus accrued and unpaid interest on the principal amount being redeemed to, but not including, the Redemption Date.

For purposes of the redemption provisions of the Securities, the following terms are applicable:    

“Business Day” means any Monday, Tuesday, Wednesday, Thursday or Friday that is not a day on which banking institutions in New York, New York are authorized or obligated by law or executive order to close. If a payment date is not a Business Day at a Place of Payment, payment may be made at that place on the next succeeding day that is a Business Day, and no interest shall accrue for the intervening period.

“Comparable Treasury Issue” means the United States Treasury security selected, in accordance with customary financial practice, by an Independent Investment Banker as having a maturity comparable to the remaining term of the Securities (assuming for this purpose that the Securities matured on November 1, 2022) (the “Remaining Life”) to be redeemed that would be utilized, at the time of selection and in accordance with customary financial practice, in pricing new issues of corporate debt securities of comparable maturity to the remaining term of such Securities (assuming that the Securities matured on November 1, 2022).

“Comparable Treasury Price” means, with respect to any Redemption Date, (1) the average, as determined by the Partnership, of the Reference Treasury Dealer Quotations for such Redemption Date, after excluding the highest and lowest Reference Treasury Dealer Quotations, or (2) if the Partnership obtains fewer than four such Reference Treasury Dealer Quotations, the average of all such quotations.

“Independent Investment Banker” means one of the Reference Treasury Dealers that the Partnership appoints to act as the Independent Investment Banker from time to time.

“Reference Treasury Dealer” means at least four primary U.S. Government securities dealers in The City of New York as the Partnership shall select.

“Reference Treasury Dealer Quotations” means, with respect to each Reference Treasury Dealer and any Redemption Date, the average, as determined by the Partnership, of the bid and asked prices for the Comparable Treasury Issue (expressed in each case as a percentage of its principal amount) quoted in writing to the Partnership by such Reference Treasury Dealer at 3:30 p.m., New York City time, on the third Business Day preceding such Redemption Date.

“Treasury Rate” means, as of any Redemption Date, the rate per year equal to: (1) the yield, under the heading which represents the average for the immediately preceding week, appearing in, or available through, the most recently published statistical release designated “H.15” or any successor publication which is published weekly by the Board of Governors of the Federal Reserve System (or companion online data resource published by the Board of Governors of the Federal Reserve System) and which established yields on actively traded United States Treasury securities adjusted to constant maturity under the caption “Treasury Constant Maturities,” for the maturity corresponding to the applicable Comparable Treasury Issue; provided that, if no maturity is within three months before or after the Remaining Life of the Notes to be redeemed, yields for the two published maturities most closely corresponding to the applicable Comparable Treasury Issue will be determined and the Treasury Rate will be interpolated or extrapolated from such yields on a straight line basis, rounding to the nearest month; or (2) if such release (or any successor release) is not published during the week preceding the calculation date or does not contain such yields, the rate per year equal to the semi-annual equivalent yield to maturity of the applicable Comparable Treasury Issue, calculated using a price for the applicable Comparable Treasury Issue (expressed as a percentage of its principal amount) equal to the related Comparable Treasury Price for such Redemption Date. The Treasury Rate will be calculated by the Partnership on the third Business Day preceding the Redemption Date.

Notice of the redemption will be transmitted to holders of Securities at least 10 and not more than 60 days prior to the Redemption Date. If fewer than all of the Securities are to be redeemed, the Trustee will select the particular Securities or portions thereof for redemption from the outstanding Securities not previously called by any of the following methods: (i) in compliance with the requirements of the principal national securities exchange, if any, on which such Securities are listed, (2) on a pro rata basis to the extent practicable and in accordance with the procedures of the Depositary or (3) by lot or in such other similar method in accordance with the procedures of the depositary of such Securities.

Unless the Partnership defaults in payment of the redemption price, on or after the Redemption Date, interest will cease to accrue on the Securities or portions thereof called for redemption.

In the event of redemption of this Security in part only, a new Security or Securities of this series and of like tenor for the unredeemed portion hereof will be issued in the name of the Holder hereof upon the cancellation hereof.

The Indenture contains provisions for defeasance at any time of the entire indebtedness of this Security or of certain restrictive covenants and Events of Default with respect to this Security, in each case upon compliance with certain conditions set forth in the Indenture.

The Indenture contains provisions permitting the Partnership and the Trustee to modify the Indenture or any supplemental indenture without the consent of the Holders for one or more of the following purposes: (1) to evidence the succession of another Person to the Partnership; (2) to surrender any right or power conferred by the Indenture, to add to the covenants for the protection of the Holders of the Securities or to add additional defaults or events of default; (3) to cure any ambiguity, to correct or supplement any provision of the Indenture which may be defective or inconsistent with any other provision of the Indenture, or to make any other provisions with respect to matters or questions arising under the Indenture as shall not adversely affect the interests of the Holders; (4) to permit qualification of the Indenture or any supplemental indenture under the TIA; (5) to permit or facilitate the issuance of Debt Securities of any series in uncertificated form; (6) to secure any or all Debt Securities; (7) to make any change that does not adversely affect the rights of any Holder; (8) to add to, change or eliminate any of the provisions of the Indenture in respect of one or more Debt Securities, under certain conditions specified therein; (9) to evidence and provide acceptance of appointment thereunder by a successor or separate Trustee and to add to or change the provisions under the Indenture as necessary; and (10) to establish the form or terms of Debt Securities of a particular series as permitted by Sections 2.01 and 2.03 of the Indenture.

The Indenture also permits, with certain exceptions as therein provided, the amendment thereof and the modification of the rights and obligations of the Partnership and the rights of the Holders of the Securities of each series to be affected under the Indenture at any time by the Partnership and the Trustee with the consent of the Holders of not less than a majority in aggregate principal amount of the Securities at the time

Outstanding of each series to be affected. The Indenture also contains provisions permitting the Holders of at least a majority in aggregate principal amount of the Securities at the time Outstanding, on behalf of the Holders of all Securities, to waive compliance by the Partnership with certain provisions of the Indenture and certain past defaults under the Indenture and their consequences. Any such consent or waiver by the Holder of this Security shall be conclusive and binding upon such Holder and upon all future Holders of this Security and of any Security issued upon the registration of transfer hereof or in exchange herefor or in lieu hereof, whether or not notation of such consent or waiver is made upon this Security.

As provided in and subject to the provisions of the Indenture, the Holder of this Security shall not have the right to institute any proceeding with respect to the Indenture or for the appointment of a receiver or trustee or for any other remedy thereunder, unless such Holder shall have previously given the Trustee written notice of a continuing Event of Default with respect to the Securities, the Holders of not less than 25% in aggregate principal amount of the Securities then Outstanding shall have made written request to the Trustee to institute proceedings in respect of such Event of Default as Trustee and offered the Trustee indemnity, and the Trustee shall not have received from the Holders of a majority in principal amount of the Securities then Outstanding a direction inconsistent with such request, and shall have failed to institute any such proceeding, for 60 days after receipt of such notice, request and offer of indemnity. The foregoing shall not apply to any suit instituted by the Holder of this Security for the enforcement of any payment of principal hereof or any premium or interest hereon on or after the respective due dates expressed herein.

No reference herein to the Indenture and no provision of this Security or of the Indenture shall alter or impair the obligation of the Partnership, which is absolute and unconditional, to pay the principal of and any premium and interest on this Security at the times, place and rate, and in the coin or currency, herein prescribed.

As provided in the Indenture and subject to certain limitations therein set forth, the transfer of this Security is registrable in the Debt Security Register, upon surrender of this Security for registration of transfer at the office or agency of the Partnership in any place where the principal of and any premium and interest on this Security are payable, duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Partnership and the Registrar duly executed by, the Holder hereof or his attorney duly authorized in writing, and thereupon one or more new Securities and of like tenor, of authorized denominations and for the same aggregate principal amount, will be issued to the designated transferee or transferees.

The Securities are issuable only in registered form without coupons in denominations of $2,000 and integral multiples of $1,000 in excess thereof. As provided in the Indenture and subject to certain limitations therein set forth, the Securities are exchangeable for a like aggregate principal amount of Securities and of like tenor of a different authorized denomination, as requested by the Holder surrendering the same.

No service charge shall be made for any such registration of transfer or exchange, but, subject to any applicable provisions of the Indenture, the Partnership may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection therewith.

Prior to due presentment of this Security for registration of transfer, the Partnership, the Trustee and any agent of the Partnership or the Trustee may treat the Person in whose name this Security is registered as the owner hereof for all purposes, whether or not this Security be overdue, and neither the Partnership, the Trustee nor any such agent shall be affected by notice to the contrary.

All terms used in this Security which are defined in the Indenture shall have the meaning assigned to them in the Indenture.

FORM OF ASSIGNMENT

ABBREVIATIONS

Customary abbreviations may be used in the name of a Securityholder or an assignee, such as TEN COM (=tenants in common), TEN ENT (=tenants by the entireties), JT TEN (=joint tenants with rights of survivorship and not as tenants in common), CUST (=custodian), and U/G/M/A (=Uniform Gift to Minors Act).

Additional abbreviations may also be used though not in the above list.

FOR VALUE RECEIVED, the undersigned hereby sell(s),

assign(s) and transfer(s) unto

Please insert Social Security or

other identifying number of assignee

PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING POSTAL ZIP CODE, OF ASSIGNEE

the within Security and all rights thereunder, hereby irrevocably constituting and appointing                              attorney to transfer said Security on the books of the Partnership, with full power of substitution in the premises.

EXHIBIT B

FORM OF CERTIFICATE TO BE DELIVERED UPON EXCHANGE OR REGISTRATION OF TRANSFER OF NOTES

Re: 3.500% Senior Notes due 2022 (the “Notes”) of MPLX LP (the “Partnership”)

This Certificate relates to $                     principal amount of Notes held in book-entry or definitive form by (the “Transferor”). The Transferor has requested the Registrar by written order to exchange or register the transfer of a Note or Notes or beneficial interests therein (the “Transfer”).

In connection with such request and in respect of each such Note or beneficial interest therein, the Transferor does hereby certify that the Transferor is familiar with the Indenture relating to the above-captioned Notes and that the Transfer does not require registration under the Securities Act of 1933, as amended (the “Securities Act”), because:

Fill in blank or check appropriate item, as applicable.

EXHIBIT C

FORM OF CERTIFICATE TO BE DELIVERED IN CONNECTION WITH TRANSFERS PURSUANT TO REGULATION S

Re: 3.500% Senior Notes due 2022 (the “Notes”) of MPLX LP (the “Partnership”)

This Certificate relates to $                      principal amount of Notes held in book-entry form by (the “Transferor”).

The Transferor has requested the Registrar by written order to exchange or register the transfer of a Note or Notes or beneficial interests therein (the “Transfer”) for an interest in the Regulation S Temporary Global Note to be held with [Euroclear] [Clearstream] through the Depositary (in each case as defined in the Indenture related to the above-referenced Notes).

In connection with such request and in respect of each such Note or beneficial interest therein, the Transferor does hereby certify that the Transferor is familiar with such Indenture and Establishment Action and that:

(a) the offer of such Notes or beneficial interests was not made to a person in the United States or for the benefit of a person in the United States (other than an Initial Purchaser);

(b) at the time the buy order was originated, the transferee was outside the United States or the Transferor and any person acting on its behalf reasonably believed that the transferee was outside the United States; or the transaction was executed in, on or through the facilities of a designated offshore securities market and neither the Transferor nor any person acting on its behalf knows that the transaction was prearranged with a buyer in the United States;

(c) no directed selling efforts have been made by the Transferor in the United States in contravention of the requirements of Rule 903(a) or Rule 904(a) of Regulation S under the U.S. Securities Act of 1933, as amended (the “Securities Act”), as applicable;

(d) the transaction is not part of a plan or scheme to evade the registration requirements of the Securities Act; and

(e) if the proposed transfer is being made prior to the expiration of a 40-day “distribution compliance period” as defined in Regulation S under the Securities Act, the transfer is being made (a) to a person that is not a U.S. person or for the account or benefit of a person that is not a U.S. person within the meaning of Regulation S under the Securities Act; or (b) to a “qualified institutional buyer” within the meaning of Rule 144A under the Securities Act, in each case that holds such Note or beneficial interests through [Euroclear] [Clearstream].

EXHIBIT 4.3

NINETEENTH SUPPLEMENTAL INDENTURE

THIS NINETEENTH SUPPLEMENTAL INDENTURE, dated as of September 23, 2019 (this “Supplemental Indenture”), is between MPLX LP, a limited partnership duly formed and existing under the laws of the State of Delaware (the “Partnership”), and The Bank of New York Mellon Trust Company, N.A., a national banking association, as trustee (the “Trustee”).

WITNESSETH

WHEREAS, pursuant to the Senior Indenture, dated as of February 12, 2015 (the “Base Indenture”), as supplemented by the First Supplemental Indenture, dated as of February 12, 2015, the Second Supplemental Indenture, dated as of December 22, 2015, the Third Supplemental Indenture, dated as of December 22, 2015, the Fourth Supplemental Indenture, dated as of December 22, 2015, the Fifth Supplemental Indenture, dated as of December 22, 2015, the Sixth Supplemental Indenture, dated as of February 10, 2017, the Seventh Supplemental Indenture, dated as of February 10, 2017, the Eighth Supplemental Indenture, dated as of February 8, 2018, the Ninth Supplemental Indenture, dated as of February 8, 2018, the Tenth Supplemental Indenture, dated as of February 8, 2018, the Eleventh Supplemental Indenture, dated as of February 8, 2018, the Twelfth Supplemental Indenture, dated as of February 8, 2018, the Thirteenth Supplemental Indenture, dated as of November 15, 2018, the Fourteenth Supplemental Indenture, dated as of November 15, 2018, the Fifteenth Supplemental Indenture, dated as of September 9, 2019, the Sixteenth Supplemental Indenture, dated as of September 9, 2019, the Seventeenth Supplemental Indenture, dated as of September 23, 2019, and the Eighteenth Supplemental Indenture, dated as of September 23, 2019 (as so supplemented, the “Indenture”), in each case between the Partnership and the Trustee, the Partnership may from time to time issue and sell Debt Securities in one or more series;

WHEREAS, the Partnership desires to create and authorize a new series of Debt Securities entitled “6.375% Senior Notes due 2024” (the “Notes”), limited initially to $380,521,000 in aggregate principal amount, and to provide the terms and conditions upon which the Notes are to be executed, registered, authenticated, issued and delivered, the Partnership has duly authorized the execution and delivery of this Supplemental Indenture;

WHEREAS, the Notes are a series of Debt Securities and are being issued under the Indenture, as supplemented by this Supplemental Indenture, and are subject to the terms contained therein and herein;

WHEREAS, the Notes are to be substantially in the form attached hereto as Exhibit A; and

WHEREAS, all acts and things necessary to make the Notes, when executed by the Partnership and authenticated and delivered by or on behalf of the Trustee as provided in the Indenture and this Supplemental Indenture, the valid, binding and legal obligations of the Partnership, and to make this Supplemental Indenture a legal, binding and enforceable agreement, have been done and performed.

NOW, THEREFORE, in order to declare the terms and conditions upon which the Notes are executed, registered, authenticated, issued and delivered, and in consideration of the foregoing premises and the purchase of such Notes by the Holders thereof, the Partnership and the Trustee mutually covenant and agree, for the equal and proportionate benefit of the Holders from time to time of the Notes, as follows:

Section 1. Definitions. Terms used in this Supplemental Indenture and not defined herein shall have the respective meanings given such terms in the Indenture.

Section 2. Other Definitions. In addition, the following terms shall have the following meanings with respect to the Notes:

“Additional Interest” means “Additional Interest” payable pursuant to the Registration Rights Agreement.

“Board Resolution” means a copy of a resolution or resolutions of the Board of Directors, certified by the Secretary or an Assistant Secretary of the General Partner to be in full force and effect on the date of such certification, and delivered to the Trustee.

“Clearstream” means Clearstream Banking, société anonyme, or any successor securities clearing agency.

“Consolidated Net Tangible Assets” means the aggregate value of all assets of the Partnership and its Subsidiaries after deducting therefrom: (i) all current liabilities, excluding all short-term indebtedness and the current portion of long-term indebtedness; (ii) all investments in unconsolidated subsidiaries and all investments accounted for on the equity basis; and (iii) all goodwill patents and trademarks, unamortized debt discounts and other similar intangibles (all determined in conformity with generally accepted accounting principles and calculated on a basis consistent with the Partnership’s most recent audited consolidated financial statements).

“Euroclear” means Euroclear Bank S.A./N.V., as operator of Euroclear systems Clearance System or any successor securities clearing agency.

“Exchange Global Notes” has the meaning set forth in Section 7(a) herein.

“Exchange Notes” means any notes issued in exchange for Notes pursuant to the Registration Rights Agreement or similar agreement.

“Global Notes” has the meaning set forth in Section 7(c) herein.

“Interest Payment Date,” when used with respect to any installment of interest on any Debt Security, means the date specified in such Debt Security as the fixed date on which such installment of interest is due and payable.

2

“Mortgage” means as the context may require, (i) to mortgage, pledge, encumber or subject to a lien or (ii) a mortgage, pledge, encumbrance or lien.

“Predecessor Security” of any particular Debt Security means every previous Debt Security evidencing all or a portion of the same debt as that evidenced by such particular Debt Security; and, for the purposes of this definition, any Debt Security authenticated and delivered under Section 2.09 of the Base Indenture in exchange for or in lieu of a mutilated, destroyed, lost or stolen Debt Security shall be deemed to evidence the same debt as the mutilated, destroyed, lost or stolen Debt Security.

“QIB” means a “qualified institutional buyer” as defined in Rule 144A.

“Registration Rights Agreement” means the registration rights agreement, dated as of the date of this Supplemental Indenture, by and among the Partnership, the General Partner, Barclays Capital Inc., MUFG Securities Americas Inc. and Wells Fargo Securities, LLC.

“Regular Record Date” for the interest payable on any Interest Payment Date on the Debt Securities means the date specified for that purpose as contemplated by Section 2.03 of the Base Indenture.

“Regulation S” means Regulation S promulgated under the Securities Act.

“Regulation S Global Notes” has the meaning set forth in Section 7(c) herein.

“Regulation S Notes” has the meaning set forth in Section 7(c) herein.

“Restricted Notes Legend” has the meaning set forth in Section 7(d) herein.

“Restricted Period” has the meaning set forth in Section 7(c) herein.

“Rule 144” means Rule 144 promulgated under the Securities Act.

“Rule 144A” means Rule 144A promulgated under the Securities Act.

“Rule 144A Global Notes” has the meaning set forth in Section 7(b) herein.

“Rule 144A Notes” has the meaning set forth in Section 7(b) herein.

“Special Record Date” for the payment of any Defaulted Interest means a date fixed by the Trustee pursuant to Section 2.17 of the Base Indenture.

“Transfer Restricted Note” means any Note that bears or is required to bear the Restricted Notes Legend.

“U.S. person” means a “U.S. person” as defined in Regulation S.

3

Section 3. Creation and Authorization of Series.

(a) There is hereby created and authorized the following new series of Debt Securities to be issued under the Indenture, to be designated as the “6.375% Senior Notes due 2024.”

(b) The Notes shall be limited initially to $380,521,000 in aggregate principal amount. Notwithstanding the foregoing initial aggregate principal amount, the Partnership may, from time to time, without notice to or consent of the Holders of the Notes, increase the principal amount of the Notes that may be issued under this Supplemental Indenture and issue such increased principal amount (or any portion thereof), in which case any additional Notes so issued will have the same terms and conditions other than the public offering price, original interest accrual date and initial interest payment date, and the same CUSIP numbers as the applicable series of Notes previously issued, will be fungible with the applicable series of Notes previously issued for U.S. federal income tax purposes, and will carry the same right to receive accrued and unpaid interest as the Notes previously issued, and such additional notes will form a single series with the Notes of such series previously issued, including, without limitation, for purposes of waivers, amendments, redemptions and, if any, offers to purchase, and will rank equally and ratably with the Notes of such series previously issued.

(c) The date on which the principal is payable on the Notes, unless accelerated pursuant to the Indenture, shall be as provided in the form of security attached hereto as Exhibit A.

(d) The Notes shall bear interest as provided in the form of security attached hereto as Exhibit A. The Interest Payment Dates and the Regular Record Dates for the determination of Holders of the Notes to whom such interest is payable shall be as provided in the form of security attached hereto as Exhibit A. Additional Interest, if any, will be payable in arrears on each Interest Payment Date following accrual in the same manner as regular interest on the Notes.

(e) The Notes shall be redeemable at the option of the Partnership as set forth in the form of security attached hereto as Exhibit A.

(f) The provisions of Sections 3.04 and 3.05 of the Base Indenture shall not be applicable to the Notes.

(g) The Notes will be issued only in fully registered form, without coupons, in denominations provided herein and in the form of security attached hereto as Exhibit A.

(h) The Events of Default and covenants specified in the Indenture will apply to the Notes.

(i) The defeasance and covenant defeasance provisions of Article XI of the Indenture, including both Sections 11.02 and 11.03 of the Base Indenture, will apply to the Notes.

4

(j) The Notes shall be issued in the form of one or more Global Securities substantially in the form of security attached hereto as Exhibit A. The Partnership initially appoints The Depository Trust Company to act as Depositary with respect to the Notes. Additional provisions applicable to the Notes issued in the form of a Global Security are set forth in the form of security attached hereto as Exhibit A.

(k) The Notes shall be issuable only in denominations of $2,000 and integral multiples of $1,000 in excess thereof.

(l) The Trustee will initially act as the Registrar for the Notes and as the paying agent with respect to the Notes. The Place of Payment will be The Bank of New York Mellon Trust Company, N.A., 240 Greenwich Street, New York, New York 10286.

(m) Except as otherwise set forth herein and in the Notes, the terms of the Notes shall be as set forth in the Indenture, including those made part of the Indenture by reference to the TIA.

Section 4. Additional Covenants. In addition to the covenants set forth in Article IV of the Indenture, the following additional covenants shall apply with respect to the Notes:

Section 4.10 Mortgage of Certain Property.

If the Partnership or any Subsidiary of the Partnership shall Mortgage as security for any indebtedness for money borrowed any pipeline, terminal or other logistics or storage property or asset employed in the transportation, distribution, storage, terminalling, processing or marketing of crude oil, natural gas, condensate or refined products that (i) is located in the United States and (ii) is determined to be a principal property by the Board of Directors in its discretion, the Partnership will secure, or will cause such Subsidiary to secure, the Notes and all other Debt Securities equally and ratably with all indebtedness or obligations secured by the Mortgage then being given; provided, however, that this covenant shall not apply in the case of:

5

Notwithstanding the foregoing restriction contained in this Section 4.10, the Partnership may and may permit its Subsidiaries to incur liens or grant Mortgages on property covered by the restriction above so long as the net book value of the property so encumbered, together with all property subject to the restriction on sale and leasebacks contained in Section 4.11, does not, at the time such lien or Mortgage is granted, exceed fifteen percent (15%) of Consolidated Net Tangible Assets.

Section 4.11 Sale and Leaseback of Certain Properties.

The Partnership will not, nor will it permit any Subsidiary of the Partnership to, sell or transfer any pipeline, terminal or other logistics or storage property or asset employed in the transportation, distribution, storage, terminalling, processing or marketing of crude oil, natural gas, condensate or refined products that (i) is located in the United States and (ii) is determined to be a principal property by the Board of Directors in its discretion, with the intention of taking back a lease of such property; provided, however, this covenant shall not apply if:

6

In the event of such a sale or transfer, the Partnership shall deliver to the Trustee the Board Resolution referred to in the parenthetical phrase contained in subclause (4)(B) of this Section 4.11 and an Officer’s Certificate setting forth all material facts under this Section 4.11.

For the purposes of this Section 4.11, the term retirement of such funded debt shall include the “in substance defeasance” of such funded debt in accordance with then applicable accounting rules.

7

Section 5. Consolidation, Merger, Sale or Conveyance. With respect to the Notes, Section 10.01 of the Base Indenture shall be amended to include the following language at the end of such section:

For purposes of this Section 10.01, “substantially all of its assets” shall mean, at any date, a portion of the non-current assets reflected in the Partnership’s consolidated balance sheet as of the end of the most recent quarterly period that represents at least sixty-six and two-thirds percent (66 2/3%) of the total reported value of such assets.

Section 6. Transfer Restrictions.

(a) The initial offering and sale of the Notes shall not be registered under the Securities Act or any state securities laws. The Notes shall be offered pursuant to exemptions from the registration requirements of the Securities Act in reliance upon Rule 144A and Regulation S promulgated under the Securities Act. For so long as any of the Notes constitute “restricted securities” within the meaning of Rule 144(a)(3) promulgated under the Securities Act, the Partnership shall, if the Partnership is not then subject to the reporting requirements of Section 13 or 15(d) of the Exchange Act, furnish to any Holder or beneficial owner of such Notes, or to any prospective purchaser of such Notes designated by such Holder or beneficial owner, in each case upon the written request of such Holder, beneficial owner or prospective purchaser, the information required to be provided pursuant to Rule 144A(d)(4) promulgated under the Securities Act.

(b) The following provisions shall apply with respect to any proposed transfer of any Transfer Restricted Note prior to the expiration of the holding period applicable to sales of such Notes under Rule 144, and the Registrar shall refuse to register any transfer of such Notes not complying with the restrictions set forth in the Restricted Notes Legend and in this Section 6. In addition to the requirements set forth in Section 2.07 of the Base Indenture, Transfer Restricted Notes that are presented or surrendered for registration of transfer or exchange pursuant to Section 2.07 of the Base Indenture shall be accompanied by the following additional information and documents, as applicable, upon which the Registrar may conclusively rely:

(i) if such Transfer Restricted Notes are being delivered to the Registrar by a Holder for registration in the name of such Holder, without transfer, a certification from such Holder to that effect (in substantially the form of Exhibit B hereto);

(ii) if such Transfer Restricted Notes are being transferred (1) to a QIB in accordance with Rule 144A or (2) pursuant to an effective registration statement under the Securities Act, a certification to that effect from such Holder (in substantially the form of Exhibit B hereto);

(iii) if such Transfer Restricted Notes are being transferred pursuant to an exemption from registration in accordance with Rule 903 or Rule 904 of Regulation S, certifications to that effect from such Holder (in substantially the form of Exhibit B and Exhibit C hereto) and an opinion of counsel to that effect if the Partnership or the Trustee so requests; or

(iv) if such Transfer Restricted Notes are being transferred in reliance on and in compliance with (1) an exemption from registration in accordance with Rule 144 under the Securities Act or (2) another exemption from the registration requirements of the Securities Act, a certification to that effect from such Holder (in substantially the form of Exhibit B attached hereto) and an opinion of counsel, certification or other evidence as may reasonably be required to that effect if the Partnership or the Trustee so requests.

8

(c) A Holder of a beneficial interest in a Regulation S Global Note who wishes to transfer its interest in such Note to a QIB in accordance with Rule 144A who takes delivery in the form of a beneficial interest in the Rule 144A Global Note shall deliver to the Registrar a certification to that effect (in substantially the form of Exhibit B attached hereto) upon which the Registrar may conclusively rely. After the expiration of the Restricted Period, interests in the Regulation S Global Note may be transferred without requiring the certification set forth in this Section 6(c).

(d) The transfer and exchange of Global Notes or beneficial interests therein shall be effected through the Depositary, in accordance with Section 2.07 of the Base Indenture and Section 6 and Section 7 hereof (including the restrictions on transfer set forth therein and herein) and the rules and procedures of the Depositary therefor, which shall include restrictions on transfer comparable to those set forth therein and herein to the extent required by the Securities Act; provided, however, that prior to the expiration of the Restricted Period, transfers and exchanges of beneficial interests in the Regulation S Global Note may be made pursuant to such restrictions only (1) to a Person that is not a U.S. person or for the account or benefit of a Person that is not a U.S. person within the meaning of Regulation S under the Securities Act or (2) to a QIB, in each case that hold such interests through Euroclear or Clearstream.

(e) If Notes are issued upon the registration of transfer, exchange or replacement of Notes not bearing the Restricted Notes Legend, the Notes so issued shall not bear such legend. If Notes are issued upon the registration or transfer, exchange or replacement of Notes bearing the Restricted Notes Legend, or if a request is made to remove the Restricted Notes Legend on a Note, the Notes so issued shall bear the Restricted Notes Legend, or the Restricted Notes Legend shall not be removed, as the case may be, unless there is delivered to the Partnership such satisfactory evidence, which may include an opinion of counsel of recognized standing licensed to practice law in the State of New York and experienced in matters involving the Securities Act, as may be reasonably required by the Partnership that neither the Restricted Notes Legend nor the restrictions on transfer set forth therein are required to ensure that transfers thereof comply with the provisions of Rule 144A, Rule 144 or Regulation S, that such Notes are not “restricted securities” within the meaning of Rule 144 or that such Notes were transferred pursuant to an effective registration statement under the Securities Act. Upon provision of such satisfactory evidence, the Trustee, at the direction of the Partnership, shall authenticate and deliver a Note that does not bear the Restricted Notes Legend. If a Restricted Notes Legend is removed from the face of a Note and the Note is subsequently held by an Affiliate of the Partnership, the Restricted Notes Legend shall be reinstated.

(f) Neither the Trustee nor the Registrar shall have any obligation or duty to monitor, determine or inquire as to compliance with any restrictions on transfer imposed under this Supplemental Indenture or under applicable law with respect to any transfer of any interest in any Note (including any transfers between or among Depositary participants or beneficial owners of interests in any Global Note) other than to require delivery of such certificates and other documentation or evidence as are expressly required by, and to do so only if and when expressly required by the terms of, this Supplemental Indenture, and to examine the same to determine

9

substantial compliance as to form with the express requirements hereof. Notwithstanding anything herein to the contrary, neither the Trustee nor the Registrar shall have any responsibility to receive any letters, opinions or certifications, nor any responsibility to monitor compliance with any transfer restrictions, in connection with any transfer or exchange of any beneficial interest in a Global Note for a beneficial interest in the same Global Note.

(g) Notwithstanding the foregoing, in the event that any Transfer Restricted Notes are exchanged for Exchange Notes in connection with an effective registration statement pursuant to the Registration Rights Agreement, the Partnership shall issue and, at the direction of the Partnership, the Trustee shall authenticate the Exchange Notes in exchange for Transfer Restricted Notes accepted for exchange in the exchange offer, which Exchange Notes shall not bear the Restricted Notes Legend, and the Registrar shall rescind any restriction on the transfer of such Exchange Notes.

Section 7. Form of Notes/Legends.

(a) The Notes are being offered only to (A) Persons reasonably believed to be QIBs in reliance on Rule 144A and (B) non-U.S. persons in reliance on Regulation S. Such Notes may thereafter be transferred to, among others, QIBs, and purchasers in reliance on Regulation S, in each case, in accordance with the procedures described herein. Exchange Notes exchanged for interests in the Rule 144A Notes and the Regulation S Notes will be issued in the form of permanent global notes deposited with the Trustee as hereinafter provided, including the appropriate legend set forth in the form of security attached as Exhibit A (the “Exchange Global Notes”). The Exchange Global Notes will be deposited upon issuance with, or on behalf of, the Trustee as custodian for the Depositary, duly executed by the Partnership and authenticated by the Trustee as hereinafter provided. The Exchange Global Notes may be represented by more than one certificate, if so required by the Depositary’s rules regarding the maximum principal amount to be represented by a single certificate.

(b) The Notes offered to QIBs in the United States of America in reliance on Rule 144A (the “Rule 144A Notes”) shall be issued in the form of a permanent global note including appropriate legends as set forth in the form of security attached as Exhibit A (the “Rule 144A Global Notes”), deposited with the Trustee, as custodian for the Depositary, duly executed by the Partnership and authenticated by the Trustee as hereinafter provided. The Rule 144A Global Notes may be represented by more than one certificate, if so required by the Depositary’s rules regarding the maximum principal amount to be represented by a single certificate. The aggregate principal amount of the Rule 144A Global Notes may from time to time be increased or decreased by adjustments made on the records of the Trustee, as custodian for the Depositary, or its nominee, as hereinafter provided.

(c) The Notes offered to non-U.S. persons outside the United States of America (the “Regulation S Notes”) in reliance on Regulation S shall be issued in the form of a permanent global note including appropriate legends as set forth in the form of security attached as Exhibit A (the “Regulation S Global Notes” and, together with the Rule 144A Global Notes and the Exchange Global Notes, the “Global Notes”). Each Regulation S Global Note will be deposited upon issuance with, or on behalf of, the Trustee as custodian for the Depositary. Prior

10

to the 40th day after the date the Notes are issued (such period through and including such 40th day, the “Restricted Period”), interests in the Regulation S Global Notes may only be transferred to non-U.S. persons pursuant to Regulation S, unless exchanged for interests in a Global Note in accordance with the transfer and certification requirements described herein. Investors may hold their interests in the Regulation S Global Note through organizations other than Euroclear or Clearstream that are participants in the Depositary’s system or directly through Euroclear or Clearstream, if they are participants in such systems, or indirectly through organizations which are participants in such systems. If such interests are held through Euroclear or Clearstream, Euroclear and Clearstream will hold such interests in the applicable Regulation S Global Note on behalf of their participants through customers’ securities accounts in their respective names on the books of their respective depositaries. Such depositaries, in turn, will hold such interests in the applicable Regulation S Global Note in customers’ securities accounts in the depositaries’ names on the books of the Depositary. The Regulation S Global Notes may be represented by more than one certificate, if so required by the Depositary’s rules regarding the maximum principal amount to be represented by a single certificate. The aggregate principal amount of the Regulation S Global Notes may from time to time be increased or decreased by adjustments made on the records of the Trustee, as custodian for the Depositary or its nominee, as hereinafter provided.

(d) Unless and until (i) a Note issued as a Transfer Restricted Note is sold under an effective registration statement, (ii) a Note issued as a Transfer Restricted Note is exchanged for an Exchange Note in connection with an effective registration statement pursuant to the Registration Rights Agreement or (iii) the Partnership receives an opinion of counsel satisfactory to it to the effect that neither such legend nor the related restrictions on transfer are required in order to maintain compliance with the provisions of the Securities Act:

(1) each Transfer Restricted Note shall bear the following legend on the face thereof (the “Restricted Notes Legend”):

THIS NOTE HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”), AND MAY NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED EXCEPT IN ACCORDANCE WITH THE FOLLOWING SENTENCE. BY ITS ACQUISITION HEREOF OR OF A BENEFICIAL INTEREST HEREIN, THE ACQUIRER (1) REPRESENTS THAT (A) IT AND ANY ACCOUNT FOR WHICH IT IS ACTING IS A “QUALIFIED INSTITUTIONAL BUYER” (WITHIN THE MEANING OF RULE 144A UNDER THE SECURITIES ACT) AND THAT IT EXERCISES SOLE INVESTMENT DISCRETION WITH RESPECT TO EACH SUCH ACCOUNT, OR (B) IT IS NOT A “U.S. PERSON” (WITHIN THE MEANING OF REGULATION S UNDER THE SECURITIES ACT) AND (2) AGREES FOR THE BENEFIT OF MPLX LP THAT IT WILL NOT OFFER, SELL, PLEDGE OR OTHERWISE TRANSFER THIS NOTE OR ANY BENEFICIAL INTEREST HEREIN, EXCEPT IN ACCORDANCE WITH THE SECURITIES ACT AND ANY APPLICABLE SECURITIES LAWS OF ANY STATE OF THE UNITED STATES AND ONLY (A) TO MPLX LP, (B) PURSUANT TO A REGISTRATION STATEMENT WHICH HAS BECOME EFFECTIVE UNDER THE SECURITIES ACT, (C) TO A QUALIFIED INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A UNDER THE SECURITIES ACT, (D) IN AN OFFSHORE TRANSACTION IN

11

COMPLIANCE WITH RULE 904 OF REGULATION S UNDER THE SECURITIES ACT, OR (E) PURSUANT TO AN EXEMPTION FROM REGISTRATION PROVIDED BY RULE 144 UNDER THE SECURITIES ACT OR ANY OTHER AVAILABLE EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.

PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (2)(C) ABOVE OR (2)(D) ABOVE, A DULY COMPLETED AND SIGNED CERTIFICATE (THE FORM OF WHICH MAY BE OBTAINED FROM THE TRUSTEE) MUST BE DELIVERED TO THE TRUSTEE. PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (E) ABOVE, MPLX LP RESERVES THE RIGHT TO REQUIRE THE DELIVERY OF SUCH LEGAL OPINIONS, CERTIFICATIONS OR OTHER EVIDENCE AS MAY REASONABLY BE REQUIRED IN ORDER TO DETERMINE THAT THE PROPOSED TRANSFER IS BEING MADE IN COMPLIANCE WITH THE SECURITIES ACT AND APPLICABLE STATE SECURITIES LAWS. NO REPRESENTATION IS MADE AS TO THE AVAILABILITY OF ANY RULE 144 EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.

(2) each Global Note shall bear the following legend on the face thereof:

UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (“DTC”), NEW YORK, NEW YORK, TO THE PARTNERSHIP OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO., OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

TRANSFERS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS IN WHOLE, BUT NOT IN PART, TO NOMINEES OF DTC OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR’S NOMINEE AND TRANSFERS OF PORTIONS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN THE INDENTURE REFERRED TO HEREIN.

Section 8. Effect of Supplemental Indenture. The provisions of this Supplemental Indenture are intended to supplement those of the Indenture as in effect immediately prior to the execution and delivery hereof. The Indenture shall remain in full force and effect except to the extent that the provisions of the Indenture are expressly modified by the terms of this Supplemental Indenture.

12

Section 9. Governing Law. This Supplemental Indenture and the Notes shall be governed by and construed in accordance with the law of the State of New York, without giving effect to any principles of conflicts of laws thereunder to the extent the application of the laws of another jurisdiction would be required thereby.

Section 10. Trustee Not Responsible for Recitals or Issuance of Notes. The recitals and statements contained herein shall be taken as statements of the Partnership, and the Trustee assumes no responsibility for their correctness. The Trustee makes no representations as to the validity or sufficiency of this Supplemental Indenture or of the Notes other than with respect to the Trustee’s execution of this Supplemental Indenture and authentication of the Notes. The Trustee shall not be accountable for the use or application by the Partnership of the Notes or the proceeds thereof.

Section 11. Conflict with the TIA. If any provision hereof limits, qualifies or conflicts with a provision of the TIA that is required under the TIA to be a part of and govern this Supplemental Indenture, the latter provision shall control. If any provision of this Supplemental Indenture modifies or excludes any provision of the TIA that may be so modified or excluded, the latter provision shall be deemed to apply to this Supplemental Indenture as so modified or to be excluded, as the case may be.

Section 12. Counterparts. This Supplemental Indenture may be executed in any number of counterparts, each of which shall be an original; but such counterparts shall together constitute one and the same instrument. The exchange of copies of this Supplemental Indenture and of signature pages by facsimile or electronic (i.e., “pdf” or “tif”) transmission shall constitute effective execution and delivery of this Supplemental Indenture for all purposes. Signatures of the parties hereto transmitted by facsimile or electronic (i.e., “pdf” or “tif”) transmission shall be deemed to be their original signatures for all purposes of the Supplemental Indenture as to the parties hereto and may be used in lieu of the original.

[The remainder of this page is left blank intentionally]

13

IN WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture to be duly executed as of the day and year first above written.

[Signature Page to Nineteenth Supplemental Indenture]

[Signature Page to Nineteenth Supplemental Indenture]

Exhibit A

MPLX LP

6.375% Senior Notes due 2024

[FOR GLOBAL NOTES: UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (“DTC”), NEW YORK, NEW YORK, TO THE PARTNERSHIP OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO., OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

TRANSFERS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS IN WHOLE, BUT NOT IN PART, TO NOMINEES OF DTC OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR’S NOMINEE AND TRANSFERS OF PORTIONS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN THE INDENTURE REFERRED TO HEREIN.]

[FOR TRANSFER RESTRICTED NOTES: THIS NOTE HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”), AND MAY NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED EXCEPT IN ACCORDANCE WITH THE FOLLOWING SENTENCE. BY ITS ACQUISITION HEREOF OR OF A BENEFICIAL INTEREST HEREIN, THE ACQUIRER (1) REPRESENTS THAT (A) IT AND ANY ACCOUNT FOR WHICH IT IS ACTING IS A “QUALIFIED INSTITUTIONAL BUYER” (WITHIN THE MEANING OF RULE 144A UNDER THE SECURITIES ACT) AND THAT IT EXERCISES SOLE INVESTMENT DISCRETION WITH RESPECT TO EACH SUCH ACCOUNT, OR (B) IT IS NOT A “U.S. PERSON” (WITHIN THE MEANING OF REGULATION S UNDER THE SECURITIES ACT) AND (2) AGREES FOR THE BENEFIT OF MPLX LP THAT IT WILL NOT OFFER, SELL, PLEDGE OR OTHERWISE TRANSFER THIS NOTE OR ANY BENEFICIAL INTEREST HEREIN, EXCEPT IN ACCORDANCE WITH THE SECURITIES ACT

AND ANY APPLICABLE SECURITIES LAWS OF ANY STATE OF THE UNITED STATES AND ONLY (A) TO MPLX LP, (B) PURSUANT TO A REGISTRATION STATEMENT WHICH HAS BECOME EFFECTIVE UNDER THE SECURITIES ACT, (C) TO A QUALIFIED INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A UNDER THE SECURITIES ACT, (D) IN AN OFFSHORE TRANSACTION IN COMPLIANCE WITH RULE 904 OF REGULATION S UNDER THE SECURITIES ACT, OR (E) PURSUANT TO AN EXEMPTION FROM REGISTRATION PROVIDED BY RULE 144 UNDER THE SECURITIES ACT OR ANY OTHER AVAILABLE EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.

PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (2)(C) ABOVE OR (2)(D) ABOVE, A DULY COMPLETED AND SIGNED CERTIFICATE (THE FORM OF WHICH MAY BE OBTAINED FROM THE TRUSTEE) MUST BE DELIVERED TO THE TRUSTEE. PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (E) ABOVE, MPLX LP RESERVES THE RIGHT TO REQUIRE THE DELIVERY OF SUCH LEGAL OPINIONS, CERTIFICATIONS OR OTHER EVIDENCE AS MAY REASONABLY BE REQUIRED IN ORDER TO DETERMINE THAT THE PROPOSED TRANSFER IS BEING MADE IN COMPLIANCE WITH THE SECURITIES ACT AND APPLICABLE STATE SECURITIES LAWS. NO REPRESENTATION IS MADE AS TO THE AVAILABILITY OF ANY RULE 144 EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.]

MPLX LP, a limited partnership duly formed and existing under the laws of the State of Delaware (herein called the “Partnership,” which term includes any successor Person under the Indenture hereinafter referred to), for value received, hereby promises to pay to [•] [Insert if Global Security: CEDE & CO.], or registered assigns, the principal sum of [•] Dollars ($[•]) [Insert if Global Security: , or such greater or lesser amount as indicated on the Schedule of Increases or Decreases in the Principal Amount of Securities attached hereto,] on May 1, 2024, and to pay interest thereon from May 1, 2019 or from the most recent Interest Payment Date to which interest has been paid or duly provided for, semi-annually on May 1 and November 1 in each year commencing November 1, 2019, at the rate of 6.375% per annum, until the principal hereof is paid or made available for payment. Interest on the Notes will be paid on the basis of a 360-day year consisting of twelve 30-day months. The Partnership shall pay Additional Interest, if any, on the applicable Interest Payment Date in the same manner as interest is paid on the Notes and in the amounts set forth in the Registration Rights Agreement. The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date will, as provided in such Indenture, be paid to the Person in whose name this Debt Security (or one or more Predecessor Securities) is registered at the close of business on the Regular Record Date for such interest, which shall be April 15 or October 15 (whether or not a Business Day), as the case may be, next preceding such Interest Payment Date. Any such interest not so punctually paid or duly provided for will forthwith cease to be payable to the Holder on such Regular Record Date and may either be paid to the Person in whose

name this Debt Security (or one or more Predecessor Securities) is registered at the close of business on a Special Record Date for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Debt Securities of this series not less than 10 days prior to such Special Record Date, or be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange on which the Debt Securities of this series may be listed, and upon such notice as may be required by such exchange all as more fully provided in said Indenture. If an Interest Payment Date, a Stated Maturity or a Redemption Date with respect to this Debt Security falls on a day that is not a Business Day, the payment will be made on the next Business Day and no interest will accrue for the period from and after such Interest Payment Date, Stated Maturity or Redemption Date.

Payment of the principal of (and premium, if any) and interest on this Debt Security will be made at the office or agency of the Partnership maintained for that purpose in New York, New York, in such coin or currency of the United States of America as at the time of payment is legal tender for payment of public and private debts; provided, however, that (1) payments on any Global Security shall be made by electronic (same-day) funds transfer to the Depositary and (2) at the option of the Partnership payment of interest may be made by check mailed to the address of the Person entitled thereto as such address shall appear in the Debt Security Register or by electronic funds transfer to an account maintained by the Person entitled thereto as specified in the Debt Security Register, provided that such Person shall have given the Trustee written instructions.

Reference is hereby made to the further provisions of this Debt Security set forth on the reverse hereof, which further provisions shall for all purposes have the same effect as if set forth at this place.

Unless the certificate of authentication hereon has been executed by the Trustee referred to on the reverse hereof by manual signature, this Debt Security shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose.

IN WITNESS WHEREOF, the Partnership has caused this instrument to be duly executed.

Dated:

CERTIFICATE OF AUTHENTICATION

This is one of the Debt Securities of the series designated therein referred to in the within-mentioned Indenture.

Dated:

MPLX LP

6.375% Senior Notes due 2024

This Security is one of a duly authorized issue of Debt Securities of the Partnership (herein called the “Securities”), issued and to be issued in one or more series under a Senior Indenture, dated as of February 12, 2015, as amended or supplemented to date, including as amended and supplemented by the Nineteenth Supplemental Indenture, dated as of September 23, 2019 (herein called the “Indenture,” which term shall have the meaning assigned to it in such instrument), between the Partnership and The Bank of New York Mellon Trust Company, N.A., as Trustee (herein called the “Trustee,” which term includes any successor trustee under the Indenture), and reference is hereby made to the Indenture for a statement of the respective rights, limitations of rights, duties and immunities thereunder of the Partnership, the Trustee and the Holders of the Securities and of the terms upon which the Securities are, and are to be, authenticated and delivered. This Security is one of the series designated on the face hereof initially limited in aggregate principal amount to $[•].

The Securities are subject to redemption, in whole at any time or in part from time to time, at the election of the Partnership, prior to their maturity date, at the redemption prices (expressed as percentages of the principal amount of such Securities to be redeemed) set forth below, plus accrued and unpaid interest on the principal amount being redeemed to, but not including, the Redemption Date, subject to the right of Holders of record on the relevant record date to receive interest due on the relevant Interest Payment Date, if redeemed during the twelve-month period beginning on May 1 of each of the years indicated below:

Notice of the redemption will be transmitted to holders of Securities at least 15 and not more than 60 days prior to the Redemption Date. If fewer than all of the Securities are to be redeemed, the Trustee will select the particular Securities or portions thereof for redemption from the outstanding Securities not previously called by any of the following methods: (i) in compliance with the requirements of the principal national securities exchange, if any, on which such Securities are listed, (2) on a pro rata basis to the extent practicable and in accordance with the procedures of the Depositary or (3) by lot or in such other similar method in accordance with the procedures of the depositary of such Securities.

Unless the Partnership defaults in payment of the redemption price, on or after the Redemption Date, interest will cease to accrue on the Securities or portions thereof called for redemption.

In the event of redemption of this Security in part only, a new Security or Securities of this series and of like tenor for the unredeemed portion hereof will be issued in the name of the Holder hereof upon the cancellation hereof.

The Indenture contains provisions for defeasance at any time of the entire indebtedness of this Security or of certain restrictive covenants and Events of Default with respect to this Security, in each case upon compliance with certain conditions set forth in the Indenture.

The Indenture contains provisions permitting the Partnership and the Trustee to modify the Indenture or any supplemental indenture without the consent of the Holders for one or more of the following purposes: (1) to evidence the succession of another Person to the Partnership; (2) to surrender any right or power conferred by the Indenture, to add to the covenants for the protection of the Holders of the Securities or to add additional defaults or events of default; (3) to cure any ambiguity, to correct or supplement any provision of the Indenture which may be defective or inconsistent with any other provision of the Indenture, or to make any other provisions with respect to matters or questions arising under the Indenture as shall not adversely affect the interests of the Holders; (4) to permit qualification of the Indenture or any supplemental indenture under the TIA; (5) to permit or facilitate the issuance of Debt Securities of any series in uncertificated form; (6) to secure any or all Debt Securities; (7) to make any change that does not adversely affect the rights of any Holder; (8) to add to, change or eliminate any of the provisions of the Indenture in respect of one or more Debt Securities, under certain conditions specified therein; (9) to evidence and provide acceptance of appointment thereunder by a successor or separate Trustee and to add to or change the provisions under the Indenture as necessary; and (10) to establish the form or terms of Debt Securities of a particular series as permitted by Sections 2.01 and 2.03 of the Indenture.

The Indenture also permits, with certain exceptions as therein provided, the amendment thereof and the modification of the rights and obligations of the Partnership and the rights of the Holders of the Securities of each series to be affected under the Indenture at any time by the Partnership and the Trustee with the consent of the Holders of not less than a majority in aggregate principal amount of the Securities at the time Outstanding of each series to be affected. The Indenture also contains provisions permitting the Holders of at least a majority in aggregate principal amount of the Securities at the time Outstanding, on behalf of the Holders of all Securities, to waive compliance by the Partnership with certain provisions of the Indenture and certain past defaults under the Indenture and their consequences. Any such consent or waiver by the Holder of this Security shall be conclusive and binding upon such Holder and upon all future Holders of this Security and of any Security issued upon the registration of transfer hereof or in exchange herefor or in lieu hereof, whether or not notation of such consent or waiver is made upon this Security.

As provided in and subject to the provisions of the Indenture, the Holder of this Security shall not have the right to institute any proceeding with respect to the Indenture or for the appointment of a receiver or trustee or for any other remedy thereunder, unless such Holder shall have previously given the Trustee written notice of a continuing Event of Default with respect to the Securities, the Holders of not less than 25% in aggregate principal amount of the Securities then Outstanding shall have made written request to the Trustee to institute proceedings in respect of such Event of Default as Trustee and offered the Trustee indemnity, and the Trustee shall not have received from the Holders of a majority in principal amount of the Securities then Outstanding a direction inconsistent with such request, and shall have failed to institute any such proceeding, for 60 days after receipt of such notice, request and offer of indemnity. The foregoing shall not apply to any suit instituted by the Holder of this Security for the enforcement of any payment of principal hereof or any premium or interest hereon on or after the respective due dates expressed herein.

No reference herein to the Indenture and no provision of this Security or of the Indenture shall alter or impair the obligation of the Partnership, which is absolute and unconditional, to pay the principal of and any premium and interest on this Security at the times, place and rate, and in the coin or currency, herein prescribed.

As provided in the Indenture and subject to certain limitations therein set forth, the transfer of this Security is registrable in the Debt Security Register, upon surrender of this Security for registration of transfer at the office or agency of the Partnership in any place where the principal of and any premium and interest on this Security are payable, duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Partnership and the Registrar duly executed by, the Holder hereof or his attorney duly authorized in writing, and thereupon one or more new Securities and of like tenor, of authorized denominations and for the same aggregate principal amount, will be issued to the designated transferee or transferees.

The Securities are issuable only in registered form without coupons in denominations of $2,000 and integral multiples of $1,000 in excess thereof. As provided in the Indenture and subject to certain limitations therein set forth, the Securities are exchangeable for a like aggregate principal amount of Securities and of like tenor of a different authorized denomination, as requested by the Holder surrendering the same.

No service charge shall be made for any such registration of transfer or exchange, but, subject to any applicable provisions of the Indenture, the Partnership may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection therewith.

Prior to due presentment of this Security for registration of transfer, the Partnership, the Trustee and any agent of the Partnership or the Trustee may treat the Person in whose name this Security is registered as the owner hereof for all purposes, whether or not this Security be overdue, and neither the Partnership, the Trustee nor any such agent shall be affected by notice to the contrary.

All terms used in this Security which are defined in the Indenture shall have the meaning assigned to them in the Indenture.

FORM OF ASSIGNMENT

ABBREVIATIONS

Customary abbreviations may be used in the name of a Securityholder or an assignee, such as TEN COM (=tenants in common), TEN ENT (=tenants by the entireties), JT TEN (=joint tenants with rights of survivorship and not as tenants in common), CUST (=custodian), and U/G/M/A (=Uniform Gift to Minors Act).

Additional abbreviations may also be used though not in the above list.

FOR VALUE RECEIVED, the undersigned hereby sell(s),

assign(s) and transfer(s) unto

Please insert Social Security or

other identifying number of assignee

PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING POSTAL ZIP CODE, OF ASSIGNEE

the within Security and all rights thereunder, hereby irrevocably constituting and appointing                      attorney to transfer said Security on the books of the Partnership, with full power of substitution in the premises.

EXHIBIT B

FORM OF CERTIFICATE TO BE DELIVERED UPON EXCHANGE OR REGISTRATION OF TRANSFER OF NOTES

Re: 6.375% Senior Notes due 2024 (the “Notes”) of MPLX LP (the “Partnership”)

This Certificate relates to $                     principal amount of Notes held in book-entry or definitive form by (the “Transferor”). The Transferor has requested the Registrar by written order to exchange or register the transfer of a Note or Notes or beneficial interests therein (the “Transfer”).

In connection with such request and in respect of each such Note or beneficial interest therein, the Transferor does hereby certify that the Transferor is familiar with the Indenture relating to the above-captioned Notes and that the Transfer does not require registration under the Securities Act of 1933, as amended (the “Securities Act”), because:

Fill in blank or check appropriate item, as applicable.

EXHIBIT C

FORM OF CERTIFICATE TO BE DELIVERED IN CONNECTION WITH TRANSFERS

PURSUANT TO REGULATION S

Re: 6.375% Senior Notes due 2024 (the “Notes”) of MPLX LP (the “Partnership”)

This Certificate relates to $                          principal amount of Notes held in book-entry form by (the “Transferor”).

The Transferor has requested the Registrar by written order to exchange or register the transfer of a Note or Notes or beneficial interests therein (the “Transfer”) for an interest in the Regulation S Temporary Global Note to be held with [Euroclear] [Clearstream] through the Depositary (in each case as defined in the Indenture related to the above-referenced Notes).

In connection with such request and in respect of each such Note or beneficial interest therein, the Transferor does hereby certify that the Transferor is familiar with such Indenture and Establishment Action and that:

(a) the offer of such Notes or beneficial interests was not made to a person in the United States or for the benefit of a person in the United States (other than an Initial Purchaser);

(b) at the time the buy order was originated, the transferee was outside the United States or the Transferor and any person acting on its behalf reasonably believed that the transferee was outside the United States; or the transaction was executed in, on or through the facilities of a designated offshore securities market and neither the Transferor nor any person acting on its behalf knows that the transaction was prearranged with a buyer in the United States;

(c) no directed selling efforts have been made by the Transferor in the United States in contravention of the requirements of Rule 903(a) or Rule 904(a) of Regulation S under the U.S. Securities Act of 1933, as amended (the “Securities Act”), as applicable;

(d) the transaction is not part of a plan or scheme to evade the registration requirements of the Securities Act; and

(e) if the proposed transfer is being made prior to the expiration of a 40-day “distribution compliance period” as defined in Regulation S under the Securities Act, the transfer is being made (a) to a person that is not a U.S. person or for the account or benefit of a person that is not a U.S. person within the meaning of Regulation S under the Securities Act; or (b) to a “qualified institutional buyer” within the meaning of Rule 144A under the Securities Act, in each case that holds such Note or beneficial interests through [Euroclear] [Clearstream].

EXHIBIT 4.4

TWENTIETH SUPPLEMENTAL INDENTURE

THIS TWENTIETH SUPPLEMENTAL INDENTURE, dated as of September 23, 2019 (this “Supplemental Indenture”), is between MPLX LP, a limited partnership duly formed and existing under the laws of the State of Delaware (the “Partnership”), and The Bank of New York Mellon Trust Company, N.A., a national banking association, as trustee (the “Trustee”).

WITNESSETH

WHEREAS, pursuant to the Senior Indenture, dated as of February 12, 2015 (the “Base Indenture”), as supplemented by the First Supplemental Indenture, dated as of February 12, 2015, the Second Supplemental Indenture, dated as of December 22, 2015, the Third Supplemental Indenture, dated as of December 22, 2015, the Fourth Supplemental Indenture, dated as of December 22, 2015, the Fifth Supplemental Indenture, dated as of December 22, 2015, the Sixth Supplemental Indenture, dated as of February 10, 2017, the Seventh Supplemental Indenture, dated as of February 10, 2017, the Eighth Supplemental Indenture, dated as of February 8, 2018, the Ninth Supplemental Indenture, dated as of February 8, 2018, the Tenth Supplemental Indenture, dated as of February 8, 2018, the Eleventh Supplemental Indenture, dated as of February 8, 2018, the Twelfth Supplemental Indenture, dated as of February 8, 2018, the Thirteenth Supplemental Indenture, dated as of November 15, 2018, the Fourteenth Supplemental Indenture, dated as of November 15, 2018, the Fifteenth Supplemental Indenture, dated as of September 9, 2019, the Sixteenth Supplemental Indenture, dated as of September 9, 2019, the Seventeenth Supplemental Indenture, dated as of September 23, 2019, the Eighteenth Supplemental Indenture, dated as of September 23, 2019, and the Nineteenth Supplemental Indenture, dated as of September 23, 2019 (as so supplemented, the “Indenture”), in each case between the Partnership and the Trustee, the Partnership may from time to time issue and sell Debt Securities in one or more series;

WHEREAS, the Partnership desires to create and authorize a new series of Debt Securities entitled “5.250% Senior Notes due 2025” (the “Notes”), limited initially to $707,655,000 in aggregate principal amount, and to provide the terms and conditions upon which the Notes are to be executed, registered, authenticated, issued and delivered, the Partnership has duly authorized the execution and delivery of this Supplemental Indenture;

WHEREAS, the Notes are a series of Debt Securities and are being issued under the Indenture, as supplemented by this Supplemental Indenture, and are subject to the terms contained therein and herein;

WHEREAS, the Notes are to be substantially in the form attached hereto as Exhibit A; and

WHEREAS, all acts and things necessary to make the Notes, when executed by the Partnership and authenticated and delivered by or on behalf of the Trustee as provided in the Indenture and this Supplemental Indenture, the valid, binding and legal obligations of the Partnership, and to make this Supplemental Indenture a legal, binding and enforceable agreement, have been done and performed.

NOW, THEREFORE, in order to declare the terms and conditions upon which the Notes are executed, registered, authenticated, issued and delivered, and in consideration of the foregoing premises and the purchase of such Notes by the Holders thereof, the Partnership and the Trustee mutually covenant and agree, for the equal and proportionate benefit of the Holders from time to time of the Notes, as follows:

Section 1. Definitions. Terms used in this Supplemental Indenture and not defined herein shall have the respective meanings given such terms in the Indenture.

Section 2. Other Definitions. In addition, the following terms shall have the following meanings with respect to the Notes:

“Additional Interest” means “Additional Interest” payable pursuant to the Registration Rights Agreement.

“Board Resolution” means a copy of a resolution or resolutions of the Board of Directors, certified by the Secretary or an Assistant Secretary of the General Partner to be in full force and effect on the date of such certification, and delivered to the Trustee.

“Clearstream” means Clearstream Banking, société anonyme, or any successor securities clearing agency.

“Consolidated Net Tangible Assets” means the aggregate value of all assets of the Partnership and its Subsidiaries after deducting therefrom: (i) all current liabilities, excluding all short-term indebtedness and the current portion of long-term indebtedness; (ii) all investments in unconsolidated subsidiaries and all investments accounted for on the equity basis; and (iii) all goodwill patents and trademarks, unamortized debt discounts and other similar intangibles (all determined in conformity with generally accepted accounting principles and calculated on a basis consistent with the Partnership’s most recent audited consolidated financial statements).

“Euroclear” means Euroclear Bank S.A./N.V., as operator of Euroclear systems Clearance System or any successor securities clearing agency.

“Exchange Global Notes” has the meaning set forth in Section 7(a) herein.

“Exchange Notes” means any notes issued in exchange for Notes pursuant to the Registration Rights Agreement or similar agreement.

“Global Notes” has the meaning set forth in Section 7(c) herein.

“Interest Payment Date,” when used with respect to any installment of interest on any Debt Security, means the date specified in such Debt Security as the fixed date on which such installment of interest is due and payable.

2

“Mortgage” means as the context may require, (i) to mortgage, pledge, encumber or subject to a lien or (ii) a mortgage, pledge, encumbrance or lien.

“Predecessor Security” of any particular Debt Security means every previous Debt Security evidencing all or a portion of the same debt as that evidenced by such particular Debt Security; and, for the purposes of this definition, any Debt Security authenticated and delivered under Section 2.09 of the Base Indenture in exchange for or in lieu of a mutilated, destroyed, lost or stolen Debt Security shall be deemed to evidence the same debt as the mutilated, destroyed, lost or stolen Debt Security.

“QIB” means a “qualified institutional buyer” as defined in Rule 144A.

“Registration Rights Agreement” means the registration rights agreement, dated as of the date of this Supplemental Indenture, by and among the Partnership, the General Partner, Barclays Capital Inc., MUFG Securities Americas Inc. and Wells Fargo Securities, LLC.

“Regular Record Date” for the interest payable on any Interest Payment Date on the Debt Securities means the date specified for that purpose as contemplated by Section 2.03 of the Base Indenture.

“Regulation S” means Regulation S promulgated under the Securities Act.

“Regulation S Global Notes” has the meaning set forth in Section 7(c) herein.

“Regulation S Notes” has the meaning set forth in Section 7(c) herein.

“Restricted Notes Legend” has the meaning set forth in Section 7(d) herein.

“Restricted Period” has the meaning set forth in Section 7(c) herein.

“Rule 144” means Rule 144 promulgated under the Securities Act.

“Rule 144A” means Rule 144A promulgated under the Securities Act.

“Rule 144A Global Notes” has the meaning set forth in Section 7(b) herein.

“Rule 144A Notes” has the meaning set forth in Section 7(b) herein.

“Special Record Date” for the payment of any Defaulted Interest means a date fixed by the Trustee pursuant to Section 2.17 of the Base Indenture.

“Transfer Restricted Note” means any Note that bears or is required to bear the Restricted Notes Legend.

“U.S. person” means a “U.S. person” as defined in Regulation S.

3

Section 3. Creation and Authorization of Series.

(a) There is hereby created and authorized the following new series of Debt Securities to be issued under the Indenture, to be designated as the “5.250% Senior Notes due 2025.”

(b) The Notes shall be limited initially to $707,655,000 in aggregate principal amount. Notwithstanding the foregoing initial aggregate principal amount, the Partnership may, from time to time, without notice to or consent of the Holders of the Notes, increase the principal amount of the Notes that may be issued under this Supplemental Indenture and issue such increased principal amount (or any portion thereof), in which case any additional Notes so issued will have the same terms and conditions other than the public offering price, original interest accrual date and initial interest payment date, and the same CUSIP numbers as the applicable series of Notes previously issued, will be fungible with the applicable series of Notes previously issued for U.S. federal income tax purposes, and will carry the same right to receive accrued and unpaid interest as the Notes previously issued, and such additional notes will form a single series with the Notes of such series previously issued, including, without limitation, for purposes of waivers, amendments, redemptions and, if any, offers to purchase, and will rank equally and ratably with the Notes of such series previously issued.

(c) The date on which the principal is payable on the Notes, unless accelerated pursuant to the Indenture, shall be as provided in the form of security attached hereto as Exhibit A.

(d) The Notes shall bear interest as provided in the form of security attached hereto as Exhibit A. The Interest Payment Dates and the Regular Record Dates for the determination of Holders of the Notes to whom such interest is payable shall be as provided in the form of security attached hereto as Exhibit A. Additional Interest, if any, will be payable in arrears on each Interest Payment Date following accrual in the same manner as regular interest on the Notes.

(e) The Notes shall be redeemable at the option of the Partnership as set forth in the form of security attached hereto as Exhibit A.

(f) The provisions of Sections 3.04 and 3.05 of the Base Indenture shall not be applicable to the Notes.

(g) The Notes will be issued only in fully registered form, without coupons, in denominations provided herein and in the form of security attached hereto as Exhibit A.

(h) The Events of Default and covenants specified in the Indenture will apply to the Notes.

(i) The defeasance and covenant defeasance provisions of Article XI of the Indenture, including both Sections 11.02 and 11.03 of the Base Indenture, will apply to the Notes.

4

(j) The Notes shall be issued in the form of one or more Global Securities substantially in the form of security attached hereto as Exhibit A. The Partnership initially appoints The Depository Trust Company to act as Depositary with respect to the Notes. Additional provisions applicable to the Notes issued in the form of a Global Security are set forth in the form of security attached hereto as Exhibit A.

(k) The Notes shall be issuable only in denominations of $2,000 and integral multiples of $1,000 in excess thereof.

(l) The Trustee will initially act as the Registrar for the Notes and as the paying agent with respect to the Notes. The Place of Payment will be The Bank of New York Mellon Trust Company, N.A., 240 Greenwich Street, New York, New York 10286.

(m) Except as otherwise set forth herein and in the Notes, the terms of the Notes shall be as set forth in the Indenture, including those made part of the Indenture by reference to the TIA.

Section 4. Additional Covenants. In addition to the covenants set forth in Article IV of the Indenture, the following additional covenants shall apply with respect to the Notes:

Section 4.10 Mortgage of Certain Property.

If the Partnership or any Subsidiary of the Partnership shall Mortgage as security for any indebtedness for money borrowed any pipeline, terminal or other logistics or storage property or asset employed in the transportation, distribution, storage, terminalling, processing or marketing of crude oil, natural gas, condensate or refined products that (i) is located in the United States and (ii) is determined to be a principal property by the Board of Directors in its discretion, the Partnership will secure, or will cause such Subsidiary to secure, the Notes and all other Debt Securities equally and ratably with all indebtedness or obligations secured by the Mortgage then being given; provided, however, that this covenant shall not apply in the case of:

5

Notwithstanding the foregoing restriction contained in this Section 4.10, the Partnership may and may permit its Subsidiaries to incur liens or grant Mortgages on property covered by the restriction above so long as the net book value of the property so encumbered, together with all property subject to the restriction on sale and leasebacks contained in Section 4.11, does not, at the time such lien or Mortgage is granted, exceed fifteen percent (15%) of Consolidated Net Tangible Assets.

Section 4.11 Sale and Leaseback of Certain Properties.

The Partnership will not, nor will it permit any Subsidiary of the Partnership to, sell or transfer any pipeline, terminal or other logistics or storage property or asset employed in the transportation, distribution, storage, terminalling, processing or marketing of crude oil, natural gas, condensate or refined products that (i) is located in the United States and (ii) is determined to be a principal property by the Board of Directors in its discretion, with the intention of taking back a lease of such property; provided, however, this covenant shall not apply if:

6

In the event of such a sale or transfer, the Partnership shall deliver to the Trustee the Board Resolution referred to in the parenthetical phrase contained in subclause (4)(B) of this Section 4.11 and an Officer’s Certificate setting forth all material facts under this Section 4.11.

For the purposes of this Section 4.11, the term retirement of such funded debt shall include the “in substance defeasance” of such funded debt in accordance with then applicable accounting rules.

7

Section 5. Consolidation, Merger, Sale or Conveyance. With respect to the Notes, Section 10.01 of the Base Indenture shall be amended to include the following language at the end of such section:

For purposes of this Section 10.01, “substantially all of its assets” shall mean, at any date, a portion of the non-current assets reflected in the Partnership’s consolidated balance sheet as of the end of the most recent quarterly period that represents at least sixty-six and two-thirds percent (66 2/3%) of the total reported value of such assets.

Section 6. Transfer Restrictions.

(a) The initial offering and sale of the Notes shall not be registered under the Securities Act or any state securities laws. The Notes shall be offered pursuant to exemptions from the registration requirements of the Securities Act in reliance upon Rule 144A and Regulation S promulgated under the Securities Act. For so long as any of the Notes constitute “restricted securities” within the meaning of Rule 144(a)(3) promulgated under the Securities Act, the Partnership shall, if the Partnership is not then subject to the reporting requirements of Section 13 or 15(d) of the Exchange Act, furnish to any Holder or beneficial owner of such Notes, or to any prospective purchaser of such Notes designated by such Holder or beneficial owner, in each case upon the written request of such Holder, beneficial owner or prospective purchaser, the information required to be provided pursuant to Rule 144A(d)(4) promulgated under the Securities Act.

(b) The following provisions shall apply with respect to any proposed transfer of any Transfer Restricted Note prior to the expiration of the holding period applicable to sales of such Notes under Rule 144, and the Registrar shall refuse to register any transfer of such Notes not complying with the restrictions set forth in the Restricted Notes Legend and in this Section 6. In addition to the requirements set forth in Section 2.07 of the Base Indenture, Transfer Restricted Notes that are presented or surrendered for registration of transfer or exchange pursuant to Section 2.07 of the Base Indenture shall be accompanied by the following additional information and documents, as applicable, upon which the Registrar may conclusively rely:

(i) if such Transfer Restricted Notes are being delivered to the Registrar by a Holder for registration in the name of such Holder, without transfer, a certification from such Holder to that effect (in substantially the form of Exhibit B hereto);

(ii) if such Transfer Restricted Notes are being transferred (1) to a QIB in accordance with Rule 144A or (2) pursuant to an effective registration statement under the Securities Act, a certification to that effect from such Holder (in substantially the form of Exhibit B hereto);

(iii) if such Transfer Restricted Notes are being transferred pursuant to an exemption from registration in accordance with Rule 903 or Rule 904 of Regulation S, certifications to that effect from such Holder (in substantially the form of Exhibit B and Exhibit C hereto) and an opinion of counsel to that effect if the Partnership or the Trustee so requests; or

(iv) if such Transfer Restricted Notes are being transferred in reliance on and in compliance with (1) an exemption from registration in accordance with Rule 144 under the Securities Act or (2) another exemption from the registration requirements of the Securities Act, a certification to that effect from such Holder (in substantially the form of Exhibit B attached hereto) and an opinion of counsel, certification or other evidence as may reasonably be required to that effect if the Partnership or the Trustee so requests.

8

(c) A Holder of a beneficial interest in a Regulation S Global Note who wishes to transfer its interest in such Note to a QIB in accordance with Rule 144A who takes delivery in the form of a beneficial interest in the Rule 144A Global Note shall deliver to the Registrar a certification to that effect (in substantially the form of Exhibit B attached hereto) upon which the Registrar may conclusively rely. After the expiration of the Restricted Period, interests in the Regulation S Global Note may be transferred without requiring the certification set forth in this Section 6(c).

(d) The transfer and exchange of Global Notes or beneficial interests therein shall be effected through the Depositary, in accordance with Section 2.07 of the Base Indenture and Section 6 and Section 7 hereof (including the restrictions on transfer set forth therein and herein) and the rules and procedures of the Depositary therefor, which shall include restrictions on transfer comparable to those set forth therein and herein to the extent required by the Securities Act; provided, however, that prior to the expiration of the Restricted Period, transfers and exchanges of beneficial interests in the Regulation S Global Note may be made pursuant to such restrictions only (1) to a Person that is not a U.S. person or for the account or benefit of a Person that is not a U.S. person within the meaning of Regulation S under the Securities Act or (2) to a QIB, in each case that hold such interests through Euroclear or Clearstream.

(e) If Notes are issued upon the registration of transfer, exchange or replacement of Notes not bearing the Restricted Notes Legend, the Notes so issued shall not bear such legend. If Notes are issued upon the registration or transfer, exchange or replacement of Notes bearing the Restricted Notes Legend, or if a request is made to remove the Restricted Notes Legend on a Note, the Notes so issued shall bear the Restricted Notes Legend, or the Restricted Notes Legend shall not be removed, as the case may be, unless there is delivered to the Partnership such satisfactory evidence, which may include an opinion of counsel of recognized standing licensed to practice law in the State of New York and experienced in matters involving the Securities Act, as may be reasonably required by the Partnership that neither the Restricted Notes Legend nor the restrictions on transfer set forth therein are required to ensure that transfers thereof comply with the provisions of Rule 144A, Rule 144 or Regulation S, that such Notes are not “restricted securities” within the meaning of Rule 144 or that such Notes were transferred pursuant to an effective registration statement under the Securities Act. Upon provision of such satisfactory evidence, the Trustee, at the direction of the Partnership, shall authenticate and deliver a Note that does not bear the Restricted Notes Legend. If a Restricted Notes Legend is removed from the face of a Note and the Note is subsequently held by an Affiliate of the Partnership, the Restricted Notes Legend shall be reinstated.

(f) Neither the Trustee nor the Registrar shall have any obligation or duty to monitor, determine or inquire as to compliance with any restrictions on transfer imposed under this Supplemental Indenture or under applicable law with respect to any transfer of any interest in any Note (including any transfers between or among Depositary participants or beneficial owners of interests in any Global Note) other than to require delivery of such certificates and other documentation or evidence as are expressly required by, and to do so only if and when expressly required by the terms of, this Supplemental Indenture, and to examine the same to determine

9

substantial compliance as to form with the express requirements hereof. Notwithstanding anything herein to the contrary, neither the Trustee nor the Registrar shall have any responsibility to receive any letters, opinions or certifications, nor any responsibility to monitor compliance with any transfer restrictions, in connection with any transfer or exchange of any beneficial interest in a Global Note for a beneficial interest in the same Global Note.

(g) Notwithstanding the foregoing, in the event that any Transfer Restricted Notes are exchanged for Exchange Notes in connection with an effective registration statement pursuant to the Registration Rights Agreement, the Partnership shall issue and, at the direction of the Partnership, the Trustee shall authenticate the Exchange Notes in exchange for Transfer Restricted Notes accepted for exchange in the exchange offer, which Exchange Notes shall not bear the Restricted Notes Legend, and the Registrar shall rescind any restriction on the transfer of such Exchange Notes.

Section 7. Form of Notes/Legends.

(a) The Notes are being offered only to (A) Persons reasonably believed to be QIBs in reliance on Rule 144A and (B) non-U.S. persons in reliance on Regulation S. Such Notes may thereafter be transferred to, among others, QIBs, and purchasers in reliance on Regulation S, in each case, in accordance with the procedures described herein. Exchange Notes exchanged for interests in the Rule 144A Notes and the Regulation S Notes will be issued in the form of permanent global notes deposited with the Trustee as hereinafter provided, including the appropriate legend set forth in the form of security attached as Exhibit A (the “Exchange Global Notes”). The Exchange Global Notes will be deposited upon issuance with, or on behalf of, the Trustee as custodian for the Depositary, duly executed by the Partnership and authenticated by the Trustee as hereinafter provided. The Exchange Global Notes may be represented by more than one certificate, if so required by the Depositary’s rules regarding the maximum principal amount to be represented by a single certificate.

(b) The Notes offered to QIBs in the United States of America in reliance on Rule 144A (the “Rule 144A Notes”) shall be issued in the form of a permanent global note including appropriate legends as set forth in the form of security attached as Exhibit A (the “Rule 144A Global Notes”), deposited with the Trustee, as custodian for the Depositary, duly executed by the Partnership and authenticated by the Trustee as hereinafter provided. The Rule 144A Global Notes may be represented by more than one certificate, if so required by the Depositary’s rules regarding the maximum principal amount to be represented by a single certificate. The aggregate principal amount of the Rule 144A Global Notes may from time to time be increased or decreased by adjustments made on the records of the Trustee, as custodian for the Depositary, or its nominee, as hereinafter provided.

(c) The Notes offered to non-U.S. persons outside the United States of America (the “Regulation S Notes”) in reliance on Regulation S shall be issued in the form of a permanent global note including appropriate legends as set forth in the form of security attached as Exhibit A (the “Regulation S Global Notes” and, together with the Rule 144A Global Notes and the Exchange Global Notes, the “Global Notes”). Each Regulation S Global Note will be deposited upon issuance with, or on behalf of, the Trustee as custodian for the Depositary. Prior

10

to the 40th day after the date the Notes are issued (such period through and including such 40th day, the “Restricted Period”), interests in the Regulation S Global Notes may only be transferred to non-U.S. persons pursuant to Regulation S, unless exchanged for interests in a Global Note in accordance with the transfer and certification requirements described herein. Investors may hold their interests in the Regulation S Global Note through organizations other than Euroclear or Clearstream that are participants in the Depositary’s system or directly through Euroclear or Clearstream, if they are participants in such systems, or indirectly through organizations which are participants in such systems. If such interests are held through Euroclear or Clearstream, Euroclear and Clearstream will hold such interests in the applicable Regulation S Global Note on behalf of their participants through customers’ securities accounts in their respective names on the books of their respective depositaries. Such depositaries, in turn, will hold such interests in the applicable Regulation S Global Note in customers’ securities accounts in the depositaries’ names on the books of the Depositary. The Regulation S Global Notes may be represented by more than one certificate, if so required by the Depositary’s rules regarding the maximum principal amount to be represented by a single certificate. The aggregate principal amount of the Regulation S Global Notes may from time to time be increased or decreased by adjustments made on the records of the Trustee, as custodian for the Depositary or its nominee, as hereinafter provided.

(d) Unless and until (i) a Note issued as a Transfer Restricted Note is sold under an effective registration statement, (ii) a Note issued as a Transfer Restricted Note is exchanged for an Exchange Note in connection with an effective registration statement pursuant to the Registration Rights Agreement or (iii) the Partnership receives an opinion of counsel satisfactory to it to the effect that neither such legend nor the related restrictions on transfer are required in order to maintain compliance with the provisions of the Securities Act:

(1) each Transfer Restricted Note shall bear the following legend on the face thereof (the “Restricted Notes Legend”):

THIS NOTE HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”), AND MAY NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED EXCEPT IN ACCORDANCE WITH THE FOLLOWING SENTENCE. BY ITS ACQUISITION HEREOF OR OF A BENEFICIAL INTEREST HEREIN, THE ACQUIRER (1) REPRESENTS THAT (A) IT AND ANY ACCOUNT FOR WHICH IT IS ACTING IS A “QUALIFIED INSTITUTIONAL BUYER” (WITHIN THE MEANING OF RULE 144A UNDER THE SECURITIES ACT) AND THAT IT EXERCISES SOLE INVESTMENT DISCRETION WITH RESPECT TO EACH SUCH ACCOUNT, OR (B) IT IS NOT A “U.S. PERSON” (WITHIN THE MEANING OF REGULATION S UNDER THE SECURITIES ACT) AND (2) AGREES FOR THE BENEFIT OF MPLX LP THAT IT WILL NOT OFFER, SELL, PLEDGE OR OTHERWISE TRANSFER THIS NOTE OR ANY BENEFICIAL INTEREST HEREIN, EXCEPT IN ACCORDANCE WITH THE SECURITIES ACT AND ANY APPLICABLE SECURITIES LAWS OF ANY STATE OF THE UNITED STATES AND ONLY (A) TO MPLX LP, (B) PURSUANT TO A REGISTRATION STATEMENT WHICH HAS BECOME EFFECTIVE UNDER THE SECURITIES ACT, (C) TO A QUALIFIED INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A UNDER THE SECURITIES ACT, (D) IN AN OFFSHORE TRANSACTION IN

11

COMPLIANCE WITH RULE 904 OF REGULATION S UNDER THE SECURITIES ACT, OR (E) PURSUANT TO AN EXEMPTION FROM REGISTRATION PROVIDED BY RULE 144 UNDER THE SECURITIES ACT OR ANY OTHER AVAILABLE EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.

PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (2)(C) ABOVE OR (2)(D) ABOVE, A DULY COMPLETED AND SIGNED CERTIFICATE (THE FORM OF WHICH MAY BE OBTAINED FROM THE TRUSTEE) MUST BE DELIVERED TO THE TRUSTEE. PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (E) ABOVE, MPLX LP RESERVES THE RIGHT TO REQUIRE THE DELIVERY OF SUCH LEGAL OPINIONS, CERTIFICATIONS OR OTHER EVIDENCE AS MAY REASONABLY BE REQUIRED IN ORDER TO DETERMINE THAT THE PROPOSED TRANSFER IS BEING MADE IN COMPLIANCE WITH THE SECURITIES ACT AND APPLICABLE STATE SECURITIES LAWS. NO REPRESENTATION IS MADE AS TO THE AVAILABILITY OF ANY RULE 144 EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.

(2) each Global Note shall bear the following legend on the face thereof:

UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (“DTC”), NEW YORK, NEW YORK, TO THE PARTNERSHIP OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO., OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

TRANSFERS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS IN WHOLE, BUT NOT IN PART, TO NOMINEES OF DTC OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR’S NOMINEE AND TRANSFERS OF PORTIONS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN THE INDENTURE REFERRED TO HEREIN.

Section 8. Effect of Supplemental Indenture. The provisions of this Supplemental Indenture are intended to supplement those of the Indenture as in effect immediately prior to the execution and delivery hereof. The Indenture shall remain in full force and effect except to the extent that the provisions of the Indenture are expressly modified by the terms of this Supplemental Indenture.

12

Section 9. Governing Law. This Supplemental Indenture and the Notes shall be governed by and construed in accordance with the law of the State of New York, without giving effect to any principles of conflicts of laws thereunder to the extent the application of the laws of another jurisdiction would be required thereby.

Section 10. Trustee Not Responsible for Recitals or Issuance of Notes. The recitals and statements contained herein shall be taken as statements of the Partnership, and the Trustee assumes no responsibility for their correctness. The Trustee makes no representations as to the validity or sufficiency of this Supplemental Indenture or of the Notes other than with respect to the Trustee’s execution of this Supplemental Indenture and authentication of the Notes. The Trustee shall not be accountable for the use or application by the Partnership of the Notes or the proceeds thereof.

Section 11. Conflict with the TIA. If any provision hereof limits, qualifies or conflicts with a provision of the TIA that is required under the TIA to be a part of and govern this Supplemental Indenture, the latter provision shall control. If any provision of this Supplemental Indenture modifies or excludes any provision of the TIA that may be so modified or excluded, the latter provision shall be deemed to apply to this Supplemental Indenture as so modified or to be excluded, as the case may be.

Section 12. Counterparts. This Supplemental Indenture may be executed in any number of counterparts, each of which shall be an original; but such counterparts shall together constitute one and the same instrument. The exchange of copies of this Supplemental Indenture and of signature pages by facsimile or electronic (i.e., “pdf” or “tif”) transmission shall constitute effective execution and delivery of this Supplemental Indenture for all purposes. Signatures of the parties hereto transmitted by facsimile or electronic (i.e., “pdf” or “tif”) transmission shall be deemed to be their original signatures for all purposes of the Supplemental Indenture as to the parties hereto and may be used in lieu of the original.

[The remainder of this page is left blank intentionally]

13

IN WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture to be duly executed as of the day and year first above written.

[Signature Page to Twentieth Supplemental Indenture]

[Signature Page to Twentieth Supplemental Indenture]

Exhibit A

MPLX LP

5.250% Senior Notes due 2025

[FOR GLOBAL NOTES: UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (“DTC”), NEW YORK, NEW YORK, TO THE PARTNERSHIP OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO., OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

TRANSFERS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS IN WHOLE, BUT NOT IN PART, TO NOMINEES OF DTC OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR’S NOMINEE AND TRANSFERS OF PORTIONS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN THE INDENTURE REFERRED TO HEREIN.]

[FOR TRANSFER RESTRICTED NOTES: THIS NOTE HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”), AND MAY NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED EXCEPT IN ACCORDANCE WITH THE FOLLOWING SENTENCE. BY ITS ACQUISITION HEREOF OR OF A BENEFICIAL INTEREST HEREIN, THE ACQUIRER (1) REPRESENTS THAT (A) IT AND ANY ACCOUNT FOR WHICH IT IS ACTING IS A “QUALIFIED INSTITUTIONAL BUYER” (WITHIN THE MEANING OF RULE 144A UNDER THE SECURITIES ACT) AND THAT IT EXERCISES SOLE INVESTMENT DISCRETION WITH RESPECT TO EACH SUCH ACCOUNT, OR (B) IT IS NOT A “U.S. PERSON” (WITHIN THE MEANING OF REGULATION S UNDER THE SECURITIES ACT) AND (2) AGREES FOR THE BENEFIT OF MPLX LP THAT IT WILL NOT OFFER, SELL, PLEDGE OR OTHERWISE TRANSFER THIS NOTE OR ANY BENEFICIAL INTEREST HEREIN, EXCEPT IN ACCORDANCE WITH THE SECURITIES ACT

AND ANY APPLICABLE SECURITIES LAWS OF ANY STATE OF THE UNITED STATES AND ONLY (A) TO MPLX LP, (B) PURSUANT TO A REGISTRATION STATEMENT WHICH HAS BECOME EFFECTIVE UNDER THE SECURITIES ACT, (C) TO A QUALIFIED INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A UNDER THE SECURITIES ACT, (D) IN AN OFFSHORE TRANSACTION IN COMPLIANCE WITH RULE 904 OF REGULATION S UNDER THE SECURITIES ACT, OR (E) PURSUANT TO AN EXEMPTION FROM REGISTRATION PROVIDED BY RULE 144 UNDER THE SECURITIES ACT OR ANY OTHER AVAILABLE EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.

PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (2)(C) ABOVE OR (2)(D) ABOVE, A DULY COMPLETED AND SIGNED CERTIFICATE (THE FORM OF WHICH MAY BE OBTAINED FROM THE TRUSTEE) MUST BE DELIVERED TO THE TRUSTEE. PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (E) ABOVE, MPLX LP RESERVES THE RIGHT TO REQUIRE THE DELIVERY OF SUCH LEGAL OPINIONS, CERTIFICATIONS OR OTHER EVIDENCE AS MAY REASONABLY BE REQUIRED IN ORDER TO DETERMINE THAT THE PROPOSED TRANSFER IS BEING MADE IN COMPLIANCE WITH THE SECURITIES ACT AND APPLICABLE STATE SECURITIES LAWS. NO REPRESENTATION IS MADE AS TO THE AVAILABILITY OF ANY RULE 144 EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.]

MPLX LP, a limited partnership duly formed and existing under the laws of the State of Delaware (herein called the “Partnership,” which term includes any successor Person under the Indenture hereinafter referred to), for value received, hereby promises to pay to [●] [Insert if Global Security: CEDE & CO.], or registered assigns, the principal sum of [●] Dollars ($[●]) [Insert if Global Security: , or such greater or lesser amount as indicated on the Schedule of Increases or Decreases in the Principal Amount of Securities attached hereto,] on January 15, 2025, and to pay interest thereon from July 15, 2019 or from the most recent Interest Payment Date to which interest has been paid or duly provided for, semi-annually on January 15 and July 15 in each year commencing January 15, 2020, at the rate of 5.250% per annum, until the principal hereof is paid or made available for payment. Interest on the Notes will be paid on the basis of a 360-day year consisting of twelve 30-day months. The Partnership shall pay Additional Interest, if any, on the applicable Interest Payment Date in the same manner as interest is paid on the Notes and in the amounts set forth in the Registration Rights Agreement. The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date will, as provided in such Indenture, be paid to the Person in whose name this Debt Security (or one or more Predecessor Securities) is registered at the close of business on the Regular Record Date for such interest, which shall be January 1 or July 1 (whether or not a Business Day), as the case may be, next preceding such Interest Payment Date. Any such interest not so punctually paid or duly provided for will forthwith cease to be payable to the Holder on such Regular Record Date and may either be paid to the Person in whose

name this Debt Security (or one or more Predecessor Securities) is registered at the close of business on a Special Record Date for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Debt Securities of this series not less than 10 days prior to such Special Record Date, or be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange on which the Debt Securities of this series may be listed, and upon such notice as may be required by such exchange all as more fully provided in said Indenture. If an Interest Payment Date, a Stated Maturity or a Redemption Date with respect to this Debt Security falls on a day that is not a Business Day, the payment will be made on the next Business Day and no interest will accrue for the period from and after such Interest Payment Date, Stated Maturity or Redemption Date.

Payment of the principal of (and premium, if any) and interest on this Debt Security will be made at the office or agency of the Partnership maintained for that purpose in New York, New York, in such coin or currency of the United States of America as at the time of payment is legal tender for payment of public and private debts; provided, however, that (1) payments on any Global Security shall be made by electronic (same-day) funds transfer to the Depositary and (2) at the option of the Partnership payment of interest may be made by check mailed to the address of the Person entitled thereto as such address shall appear in the Debt Security Register or by electronic funds transfer to an account maintained by the Person entitled thereto as specified in the Debt Security Register, provided that such Person shall have given the Trustee written instructions.

Reference is hereby made to the further provisions of this Debt Security set forth on the reverse hereof, which further provisions shall for all purposes have the same effect as if set forth at this place.

Unless the certificate of authentication hereon has been executed by the Trustee referred to on the reverse hereof by manual signature, this Debt Security shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose.

IN WITNESS WHEREOF, the Partnership has caused this instrument to be duly executed.

Dated:

CERTIFICATE OF AUTHENTICATION

This is one of the Debt Securities of the series designated therein referred to in the within-mentioned Indenture.

Dated:

MPLX LP

5.250% Senior Notes due 2025

This Security is one of a duly authorized issue of Debt Securities of the Partnership (herein called the “Securities”), issued and to be issued in one or more series under a Senior Indenture, dated as of February 12, 2015, as amended or supplemented to date, including as amended and supplemented by the Twentieth Supplemental Indenture, dated as of September 23, 2019 (herein called the “Indenture,” which term shall have the meaning assigned to it in such instrument), between the Partnership and The Bank of New York Mellon Trust Company, N.A., as Trustee (herein called the “Trustee,” which term includes any successor trustee under the Indenture), and reference is hereby made to the Indenture for a statement of the respective rights, limitations of rights, duties and immunities thereunder of the Partnership, the Trustee and the Holders of the Securities and of the terms upon which the Securities are, and are to be, authenticated and delivered. This Security is one of the series designated on the face hereof initially limited in aggregate principal amount to $[•].

Prior to January 15, 2021, the Securities are subject to redemption, in whole at any time or in part from time to time, at the election of the Partnership, at a redemption price equal to the sum of (1) 100% of the principal amount thereof plus (2) the Applicable Premium, subject to the right of Holders of record on the relevant record date to receive interest due on the relevant Interest Payment Date, plus (3) accrued and unpaid interest on the principal amount being redeemed to, but not including, the Redemption Date.

On or after January 15, 2021, the Securities are subject to redemption, in whole at any time or in part from time to time, at the election of the Partnership, at the redemption prices (expressed as percentages of the principal amount of such Securities to be redeemed) set forth below, plus accrued and unpaid interest on the principal amount being redeemed to, but not including, the Redemption Date, subject to the right of Holders of record on the relevant record date to receive interest due on the relevant Interest Payment Date, if redeemed during the twelve-month period beginning on January 15 of each of the years indicated below:

For purposes of the redemption provisions of the Securities, the following terms are applicable:

“Applicable Premium” means, with respect to any Securities on any Redemption Date, the greater of: (1) 1.0% of the principal amount of such Securities; and (2) the excess of: (A) the present value at such Redemption Date of (i) the redemption price of such Securities on January 15, 2021 (such redemption price being set forth in the table appearing above), plus (ii) all required interest payments due on such Securities through January 15, 2021 (excluding accrued and unpaid interest to the Redemption Date), computed using a discount rate equal to the Treasury Rate as of such Redemption Date plus 50 basis points; over (B) the principal amount of such Securities.

“Business Day” means any Monday, Tuesday, Wednesday, Thursday or Friday that is not a day on which banking institutions in New York, New York are authorized or obligated by law or executive order to close. If a payment date is not a Business Day at a Place of Payment, payment may be made at that place on the next succeeding day that is a Business Day, and no interest shall accrue for the intervening period.

“Treasury Rate” means, with respect to any Redemption Date for the Securities, the yield to maturity as of any such redemption date of United States Treasury securities with a constant maturity (as compiled and published in the most recent Federal Reserve Statistical Release H.15 (519) that has become publicly available at least two Business Days prior to any such redemption date (or, if such Statistical Release is no longer published, any publicly available source of similar market data)) most nearly equal to the period from any such redemption date to January 15, 2021; provided, however, that if the period from any such redemption date to January 15, 2021 is less than one year, the weekly average yield on actually traded United States Treasury securities adjusted to a constant maturity of one year will be used.

Notice of the redemption will be transmitted to holders of Securities at least 15 and not more than 60 days prior to the Redemption Date. If fewer than all of the Securities are to be redeemed, the Trustee will select the particular Securities or portions thereof for redemption from the outstanding Securities not previously called by any of the following methods: (i) in compliance with the requirements of the principal national securities exchange, if any, on which such Securities are listed, (2) on a pro rata basis to the extent practicable and in accordance with the procedures of the Depositary or (3) by lot or in such other similar method in accordance with the procedures of the depositary of such Securities.

Unless the Partnership defaults in payment of the redemption price, on or after the Redemption Date, interest will cease to accrue on the Securities or portions thereof called for redemption.

In the event of redemption of this Security in part only, a new Security or Securities of this series and of like tenor for the unredeemed portion hereof will be issued in the name of the Holder hereof upon the cancellation hereof.

The Indenture contains provisions for defeasance at any time of the entire indebtedness of this Security or of certain restrictive covenants and Events of Default with respect to this Security, in each case upon compliance with certain conditions set forth in the Indenture.

The Indenture contains provisions permitting the Partnership and the Trustee to modify the Indenture or any supplemental indenture without the consent of the Holders for one or more of the following purposes: (1) to evidence the succession of another Person to the Partnership; (2) to surrender any right or power conferred by the Indenture, to add to the covenants for the protection of the Holders of the Securities or to add additional defaults or events of default; (3) to cure any ambiguity, to correct or supplement any provision of the Indenture which may be defective or inconsistent with any other provision of the Indenture, or to make any other provisions with respect to matters or questions arising under the Indenture as shall not adversely affect the interests of the Holders; (4) to permit qualification of the Indenture or any supplemental indenture under the TIA; (5) to permit or facilitate the issuance of Debt Securities of any series in uncertificated form; (6) to secure any or all Debt Securities; (7) to make any change that does not adversely affect the rights of any Holder; (8) to add to, change or eliminate any of the provisions of the Indenture in respect of one or more Debt Securities, under certain conditions specified therein; (9) to evidence and provide acceptance of appointment thereunder by a successor or separate Trustee and to add to or change the provisions under the Indenture as necessary; and (10) to establish the form or terms of Debt Securities of a particular series as permitted by Sections 2.01 and 2.03 of the Indenture.

The Indenture also permits, with certain exceptions as therein provided, the amendment thereof and the modification of the rights and obligations of the Partnership and the rights of the Holders of the Securities of each series to be affected under the Indenture at any time by the Partnership and the Trustee with the consent of the Holders of not less than a majority in aggregate principal amount of the Securities at the time Outstanding of each series to be affected. The Indenture also contains provisions permitting the Holders of at least a majority in aggregate principal amount of the Securities at the time Outstanding, on behalf of the Holders of all Securities, to waive compliance by the Partnership with certain provisions of the Indenture and certain past defaults under the Indenture and their consequences. Any such consent or waiver by the Holder of this Security shall be conclusive and binding upon such Holder and upon all future Holders of this Security and of any Security issued upon the registration of transfer hereof or in exchange herefor or in lieu hereof, whether or not notation of such consent or waiver is made upon this Security.

As provided in and subject to the provisions of the Indenture, the Holder of this Security shall not have the right to institute any proceeding with respect to the Indenture or for the appointment of a receiver or trustee or for any other remedy thereunder, unless such Holder shall have previously given the Trustee written notice of a continuing Event of Default with respect to the Securities, the Holders of not less than 25% in aggregate principal amount of the Securities then Outstanding shall have made written request to the Trustee to institute proceedings in respect of such Event of Default as Trustee and offered the Trustee indemnity, and the Trustee shall not have received from the Holders of a majority in principal amount of the Securities then Outstanding a direction inconsistent with such request, and shall have failed to institute any such proceeding, for 60 days after receipt of such notice, request and offer of indemnity. The foregoing shall not apply to any suit instituted by the Holder of this Security for the enforcement of any payment of principal hereof or any premium or interest hereon on or after the respective due dates expressed herein.

No reference herein to the Indenture and no provision of this Security or of the Indenture shall alter or impair the obligation of the Partnership, which is absolute and unconditional, to pay the principal of and any premium and interest on this Security at the times, place and rate, and in the coin or currency, herein prescribed.

As provided in the Indenture and subject to certain limitations therein set forth, the transfer of this Security is registrable in the Debt Security Register, upon surrender of this Security for registration of transfer at the office or agency of the Partnership in any place where the principal of and any premium and interest on this Security are payable, duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Partnership and the Registrar duly executed by, the Holder hereof or his attorney duly authorized in writing, and thereupon one or more new Securities and of like tenor, of authorized denominations and for the same aggregate principal amount, will be issued to the designated transferee or transferees.

The Securities are issuable only in registered form without coupons in denominations of $2,000 and integral multiples of $1,000 in excess thereof. As provided in the Indenture and subject to certain limitations therein set forth, the Securities are exchangeable for a like aggregate principal amount of Securities and of like tenor of a different authorized denomination, as requested by the Holder surrendering the same.

No service charge shall be made for any such registration of transfer or exchange, but, subject to any applicable provisions of the Indenture, the Partnership may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection therewith.

Prior to due presentment of this Security for registration of transfer, the Partnership, the Trustee and any agent of the Partnership or the Trustee may treat the Person in whose name this Security is registered as the owner hereof for all purposes, whether or not this Security be overdue, and neither the Partnership, the Trustee nor any such agent shall be affected by notice to the contrary.

All terms used in this Security which are defined in the Indenture shall have the meaning assigned to them in the Indenture.

FORM OF ASSIGNMENT

ABBREVIATIONS

Customary abbreviations may be used in the name of a Securityholder or an assignee, such as TEN COM (=tenants in common), TEN ENT (=tenants by the entireties), JT TEN (=joint tenants with rights of survivorship and not as tenants in common), CUST (=custodian), and U/G/M/A (=Uniform Gift to Minors Act).

Additional abbreviations may also be used though not in the above list.

FOR VALUE RECEIVED, the undersigned hereby sell(s),

assign(s) and transfer(s) unto

Please insert Social Security or

other identifying number of assignee

PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING POSTAL ZIP CODE, OF ASSIGNEE

the within Security and all rights thereunder, hereby irrevocably constituting and appointing                                  attorney to transfer said Security on the books of the Partnership, with full power of substitution in the premises.

EXHIBIT B

FORM OF CERTIFICATE TO BE DELIVERED UPON EXCHANGE OR REGISTRATION OF TRANSFER OF NOTES

Re: 5.250% Senior Notes due 2025 (the “Notes”) of MPLX LP (the “Partnership”)

This Certificate relates to $                 principal amount of Notes held in book-entry or definitive form by (the “Transferor”). The Transferor has requested the Registrar by written order to exchange or register the transfer of a Note or Notes or beneficial interests therein (the “Transfer”).

In connection with such request and in respect of each such Note or beneficial interest therein, the Transferor does hereby certify that the Transferor is familiar with the Indenture relating to the above-captioned Notes and that the Transfer does not require registration under the Securities Act of 1933, as amended (the “Securities Act”), because:

Fill in blank or check appropriate item, as applicable.

EXHIBIT C

FORM OF CERTIFICATE TO BE DELIVERED IN CONNECTION WITH TRANSFERS PURSUANT TO REGULATION S

Re: 5.250% Senior Notes due 2025 (the “Notes”) of MPLX LP (the “Partnership”)

This Certificate relates to $                principal amount of Notes held in book-entry form by (the “Transferor”).

The Transferor has requested the Registrar by written order to exchange or register the transfer of a Note or Notes or beneficial interests therein (the “Transfer”) for an interest in the Regulation S Temporary Global Note to be held with [Euroclear] [Clearstream] through the Depositary (in each case as defined in the Indenture related to the above-referenced Notes).

In connection with such request and in respect of each such Note or beneficial interest therein, the Transferor does hereby certify that the Transferor is familiar with such Indenture and Establishment Action and that:

(a) the offer of such Notes or beneficial interests was not made to a person in the United States or for the benefit of a person in the United States (other than an Initial Purchaser);

(b) at the time the buy order was originated, the transferee was outside the United States or the Transferor and any person acting on its behalf reasonably believed that the transferee was outside the United States; or the transaction was executed in, on or through the facilities of a designated offshore securities market and neither the Transferor nor any person acting on its behalf knows that the transaction was prearranged with a buyer in the United States;

(c) no directed selling efforts have been made by the Transferor in the United States in contravention of the requirements of Rule 903(a) or Rule 904(a) of Regulation S under the U.S. Securities Act of 1933, as amended (the “Securities Act”), as applicable;

(d) the transaction is not part of a plan or scheme to evade the registration requirements of the Securities Act; and

(e) if the proposed transfer is being made prior to the expiration of a 40-day “distribution compliance period” as defined in Regulation S under the Securities Act, the transfer is being made (a) to a person that is not a U.S. person or for the account or benefit of a person that is not a U.S. person within the meaning of Regulation S under the Securities Act; or (b) to a “qualified institutional buyer” within the meaning of Rule 144A under the Securities Act, in each case that holds such Note or beneficial interests through [Euroclear] [Clearstream].

EXHIBIT 4.5

TWENTY-FIRST SUPPLEMENTAL INDENTURE

THIS TWENTY-FIRST SUPPLEMENTAL INDENTURE, dated as of September 23, 2019 (this “Supplemental Indenture”), is between MPLX LP, a limited partnership duly formed and existing under the laws of the State of Delaware (the “Partnership”), and The Bank of New York Mellon Trust Company, N.A., a national banking association, as trustee (the “Trustee”).

WITNESSETH

WHEREAS, pursuant to the Senior Indenture, dated as of February 12, 2015 (the “Base Indenture”), as supplemented by the First Supplemental Indenture, dated as of February 12, 2015, the Second Supplemental Indenture, dated as of December 22, 2015, the Third Supplemental Indenture, dated as of December 22, 2015, the Fourth Supplemental Indenture, dated as of December 22, 2015, the Fifth Supplemental Indenture, dated as of December 22, 2015, the Sixth Supplemental Indenture, dated as of February 10, 2017, the Seventh Supplemental Indenture, dated as of February 10, 2017, the Eighth Supplemental Indenture, dated as of February 8, 2018, the Ninth Supplemental Indenture, dated as of February 8, 2018, the Tenth Supplemental Indenture, dated as of February 8, 2018, the Eleventh Supplemental Indenture, dated as of February 8, 2018, the Twelfth Supplemental Indenture, dated as of February 8, 2018, the Thirteenth Supplemental Indenture, dated as of November 15, 2018, the Fourteenth Supplemental Indenture, dated as of November 15, 2018, the Fifteenth Supplemental Indenture, dated as of September 9, 2019, the Sixteenth Supplemental Indenture, dated as of September 9, 2019, the Seventeenth Supplemental Indenture, dated as of September 23, 2019, the Eighteenth Supplemental Indenture, dated as of September 23, 2019, the Nineteenth Supplemental Indenture, dated as of September 23, 2019, and the Twentieth Supplemental Indenture, dated as of September 23, 2019 (as so supplemented, the “Indenture”), in each case between the Partnership and the Trustee, the Partnership may from time to time issue and sell Debt Securities in one or more series;

WHEREAS, the Partnership desires to create and authorize a new series of Debt Securities entitled “4.250% Senior Notes due 2027” (the “Notes”), limited initially to $731,718,000 in aggregate principal amount, and to provide the terms and conditions upon which the Notes are to be executed, registered, authenticated, issued and delivered, the Partnership has duly authorized the execution and delivery of this Supplemental Indenture;

WHEREAS, the Notes are a series of Debt Securities and are being issued under the Indenture, as supplemented by this Supplemental Indenture, and are subject to the terms contained therein and herein;

WHEREAS, the Notes are to be substantially in the form attached hereto as Exhibit A; and

WHEREAS, all acts and things necessary to make the Notes, when executed by the Partnership and authenticated and delivered by or on behalf of the Trustee as provided in the Indenture and this Supplemental Indenture, the valid, binding and legal obligations of the Partnership, and to make this Supplemental Indenture a legal, binding and enforceable agreement, have been done and performed.

NOW, THEREFORE, in order to declare the terms and conditions upon which the Notes are executed, registered, authenticated, issued and delivered, and in consideration of the foregoing premises and the purchase of such Notes by the Holders thereof, the Partnership and the Trustee mutually covenant and agree, for the equal and proportionate benefit of the Holders from time to time of the Notes, as follows:

Section 1. Definitions. Terms used in this Supplemental Indenture and not defined herein shall have the respective meanings given such terms in the Indenture.

Section 2. Other Definitions. In addition, the following terms shall have the following meanings with respect to the Notes:

“Additional Interest” means “Additional Interest” payable pursuant to the Registration Rights Agreement.

“Board Resolution” means a copy of a resolution or resolutions of the Board of Directors, certified by the Secretary or an Assistant Secretary of the General Partner to be in full force and effect on the date of such certification, and delivered to the Trustee.

“Clearstream” means Clearstream Banking, société anonyme, or any successor securities clearing agency.

“Consolidated Net Tangible Assets” means the aggregate value of all assets of the Partnership and its Subsidiaries after deducting therefrom: (i) all current liabilities, excluding all short-term indebtedness and the current portion of long-term indebtedness; (ii) all investments in unconsolidated subsidiaries and all investments accounted for on the equity basis; and (iii) all goodwill patents and trademarks, unamortized debt discounts and other similar intangibles (all determined in conformity with generally accepted accounting principles and calculated on a basis consistent with the Partnership’s most recent audited consolidated financial statements).

“Euroclear” means Euroclear Bank S.A./N.V., as operator of Euroclear systems Clearance System or any successor securities clearing agency.

“Exchange Global Notes” has the meaning set forth in Section 7(a) herein.

“Exchange Notes” means any notes issued in exchange for Notes pursuant to the Registration Rights Agreement or similar agreement.

“Global Notes” has the meaning set forth in Section 7(c) herein.

“Interest Payment Date,” when used with respect to any installment of interest on any Debt Security, means the date specified in such Debt Security as the fixed date on which such installment of interest is due and payable.

2

“Mortgage” means as the context may require, (i) to mortgage, pledge, encumber or subject to a lien or (ii) a mortgage, pledge, encumbrance or lien.

“Predecessor Security” of any particular Debt Security means every previous Debt Security evidencing all or a portion of the same debt as that evidenced by such particular Debt Security; and, for the purposes of this definition, any Debt Security authenticated and delivered under Section 2.09 of the Base Indenture in exchange for or in lieu of a mutilated, destroyed, lost or stolen Debt Security shall be deemed to evidence the same debt as the mutilated, destroyed, lost or stolen Debt Security.

“QIB” means a “qualified institutional buyer” as defined in Rule 144A.

“Registration Rights Agreement” means the registration rights agreement, dated as of the date of this Supplemental Indenture, by and among the Partnership, the General Partner, Barclays Capital Inc., MUFG Securities Americas Inc. and Wells Fargo Securities, LLC.

“Regular Record Date” for the interest payable on any Interest Payment Date on the Debt Securities means the date specified for that purpose as contemplated by Section 2.03 of the Base Indenture.

“Regulation S” means Regulation S promulgated under the Securities Act.

“Regulation S Global Notes” has the meaning set forth in Section 7(c) herein.

“Regulation S Notes” has the meaning set forth in Section 7(c) herein.

“Restricted Notes Legend” has the meaning set forth in Section 7(d) herein.

“Restricted Period” has the meaning set forth in Section 7(c) herein.

“Rule 144” means Rule 144 promulgated under the Securities Act.

“Rule 144A” means Rule 144A promulgated under the Securities Act.

“Rule 144A Global Notes” has the meaning set forth in Section 7(b) herein.

“Rule 144A Notes” has the meaning set forth in Section 7(b) herein.

“Special Record Date” for the payment of any Defaulted Interest means a date fixed by the Trustee pursuant to Section 2.17 of the Base Indenture.

“Transfer Restricted Note” means any Note that bears or is required to bear the Restricted Notes Legend.

“U.S. person” means a “U.S. person” as defined in Regulation S.

3

Section 3. Creation and Authorization of Series.

(a) There is hereby created and authorized the following new series of Debt Securities to be issued under the Indenture, to be designated as the “4.250% Senior Notes due 2027.”

(b) The Notes shall be limited initially to $731,718,000 in aggregate principal amount. Notwithstanding the foregoing initial aggregate principal amount, the Partnership may, from time to time, without notice to or consent of the Holders of the Notes, increase the principal amount of the Notes that may be issued under this Supplemental Indenture and issue such increased principal amount (or any portion thereof), in which case any additional Notes so issued will have the same terms and conditions other than the public offering price, original interest accrual date and initial interest payment date, and the same CUSIP numbers as the applicable series of Notes previously issued, will be fungible with the applicable series of Notes previously issued for U.S. federal income tax purposes, and will carry the same right to receive accrued and unpaid interest as the Notes previously issued, and such additional notes will form a single series with the Notes of such series previously issued, including, without limitation, for purposes of waivers, amendments, redemptions and, if any, offers to purchase, and will rank equally and ratably with the Notes of such series previously issued.

(c) The date on which the principal is payable on the Notes, unless accelerated pursuant to the Indenture, shall be as provided in the form of security attached hereto as Exhibit A.

(d) The Notes shall bear interest as provided in the form of security attached hereto as Exhibit A. The Interest Payment Dates and the Regular Record Dates for the determination of Holders of the Notes to whom such interest is payable shall be as provided in the form of security attached hereto as Exhibit A. Additional Interest, if any, will be payable in arrears on each Interest Payment Date following accrual in the same manner as regular interest on the Notes.

(e) The Notes shall be redeemable at the option of the Partnership as set forth in the form of security attached hereto as Exhibit A.

(f) The provisions of Sections 3.04 and 3.05 of the Base Indenture shall not be applicable to the Notes.

(g) The Notes will be issued only in fully registered form, without coupons, in denominations provided herein and in the form of security attached hereto as Exhibit A.

(h) The Events of Default and covenants specified in the Indenture will apply to the Notes.

(i) The defeasance and covenant defeasance provisions of Article XI of the Indenture, including both Sections 11.02 and 11.03 of the Base Indenture, will apply to the Notes.

4

(j) The Notes shall be issued in the form of one or more Global Securities substantially in the form of security attached hereto as Exhibit A. The Partnership initially appoints The Depository Trust Company to act as Depositary with respect to the Notes. Additional provisions applicable to the Notes issued in the form of a Global Security are set forth in the form of security attached hereto as Exhibit A.

(k) The Notes shall be issuable only in denominations of $2,000 and integral multiples of $1,000 in excess thereof.

(l) The Trustee will initially act as the Registrar for the Notes and as the paying agent with respect to the Notes. The Place of Payment will be The Bank of New York Mellon Trust Company, N.A., 240 Greenwich Street, New York, New York 10286.

(m) Except as otherwise set forth herein and in the Notes, the terms of the Notes shall be as set forth in the Indenture, including those made part of the Indenture by reference to the TIA.

Section 4. Additional Covenants. In addition to the covenants set forth in Article IV of the Indenture, the following additional covenants shall apply with respect to the Notes:

Section 4.10 Mortgage of Certain Property.

If the Partnership or any Subsidiary of the Partnership shall Mortgage as security for any indebtedness for money borrowed any pipeline, terminal or other logistics or storage property or asset employed in the transportation, distribution, storage, terminalling, processing or marketing of crude oil, natural gas, condensate or refined products that (i) is located in the United States and (ii) is determined to be a principal property by the Board of Directors in its discretion, the Partnership will secure, or will cause such Subsidiary to secure, the Notes and all other Debt Securities equally and ratably with all indebtedness or obligations secured by the Mortgage then being given; provided, however, that this covenant shall not apply in the case of:

5

Notwithstanding the foregoing restriction contained in this Section 4.10, the Partnership may and may permit its Subsidiaries to incur liens or grant Mortgages on property covered by the restriction above so long as the net book value of the property so encumbered, together with all property subject to the restriction on sale and leasebacks contained in Section 4.11, does not, at the time such lien or Mortgage is granted, exceed fifteen percent (15%) of Consolidated Net Tangible Assets.

Section 4.11 Sale and Leaseback of Certain Properties.

The Partnership will not, nor will it permit any Subsidiary of the Partnership to, sell or transfer any pipeline, terminal or other logistics or storage property or asset employed in the transportation, distribution, storage, terminalling, processing or marketing of crude oil, natural gas, condensate or refined products that (i) is located in the United States and (ii) is determined to be a principal property by the Board of Directors in its discretion, with the intention of taking back a lease of such property; provided, however, this covenant shall not apply if:

6

In the event of such a sale or transfer, the Partnership shall deliver to the Trustee the Board Resolution referred to in the parenthetical phrase contained in subclause (4)(B) of this Section 4.11 and an Officer’s Certificate setting forth all material facts under this Section 4.11.

For the purposes of this Section 4.11, the term retirement of such funded debt shall include the “in substance defeasance” of such funded debt in accordance with then applicable accounting rules.

7

Section 5. Consolidation, Merger, Sale or Conveyance. With respect to the Notes, Section 10.01 of the Base Indenture shall be amended to include the following language at the end of such section:

For purposes of this Section 10.01, “substantially all of its assets” shall mean, at any date, a portion of the non-current assets reflected in the Partnership’s consolidated balance sheet as of the end of the most recent quarterly period that represents at least sixty-six and two-thirds percent (66 2/3%) of the total reported value of such assets.

Section 6. Transfer Restrictions.

(a) The initial offering and sale of the Notes shall not be registered under the Securities Act or any state securities laws. The Notes shall be offered pursuant to exemptions from the registration requirements of the Securities Act in reliance upon Rule 144A and Regulation S promulgated under the Securities Act. For so long as any of the Notes constitute “restricted securities” within the meaning of Rule 144(a)(3) promulgated under the Securities Act, the Partnership shall, if the Partnership is not then subject to the reporting requirements of Section 13 or 15(d) of the Exchange Act, furnish to any Holder or beneficial owner of such Notes, or to any prospective purchaser of such Notes designated by such Holder or beneficial owner, in each case upon the written request of such Holder, beneficial owner or prospective purchaser, the information required to be provided pursuant to Rule 144A(d)(4) promulgated under the Securities Act.

(b) The following provisions shall apply with respect to any proposed transfer of any Transfer Restricted Note prior to the expiration of the holding period applicable to sales of such Notes under Rule 144, and the Registrar shall refuse to register any transfer of such Notes not complying with the restrictions set forth in the Restricted Notes Legend and in this Section 6. In addition to the requirements set forth in Section 2.07 of the Base Indenture, Transfer Restricted Notes that are presented or surrendered for registration of transfer or exchange pursuant to Section 2.07 of the Base Indenture shall be accompanied by the following additional information and documents, as applicable, upon which the Registrar may conclusively rely:

(i) if such Transfer Restricted Notes are being delivered to the Registrar by a Holder for registration in the name of such Holder, without transfer, a certification from such Holder to that effect (in substantially the form of Exhibit B hereto);

(ii) if such Transfer Restricted Notes are being transferred (1) to a QIB in accordance with Rule 144A or (2) pursuant to an effective registration statement under the Securities Act, a certification to that effect from such Holder (in substantially the form of Exhibit B hereto);

(iii) if such Transfer Restricted Notes are being transferred pursuant to an exemption from registration in accordance with Rule 903 or Rule 904 of Regulation S, certifications to that effect from such Holder (in substantially the form of Exhibit B and Exhibit C hereto) and an opinion of counsel to that effect if the Partnership or the Trustee so requests; or

(iv) if such Transfer Restricted Notes are being transferred in reliance on and in compliance with (1) an exemption from registration in accordance with Rule 144 under the Securities Act or (2) another exemption from the registration requirements of the Securities Act, a certification to that effect from such Holder (in substantially the form of Exhibit B attached hereto) and an opinion of counsel, certification or other evidence as may reasonably be required to that effect if the Partnership or the Trustee so requests.

8

(c) A Holder of a beneficial interest in a Regulation S Global Note who wishes to transfer its interest in such Note to a QIB in accordance with Rule 144A who takes delivery in the form of a beneficial interest in the Rule 144A Global Note shall deliver to the Registrar a certification to that effect (in substantially the form of Exhibit B attached hereto) upon which the Registrar may conclusively rely. After the expiration of the Restricted Period, interests in the Regulation S Global Note may be transferred without requiring the certification set forth in this Section 6(c).

(d) The transfer and exchange of Global Notes or beneficial interests therein shall be effected through the Depositary, in accordance with Section 2.07 of the Base Indenture and Section 6 and Section 7 hereof (including the restrictions on transfer set forth therein and herein) and the rules and procedures of the Depositary therefor, which shall include restrictions on transfer comparable to those set forth therein and herein to the extent required by the Securities Act; provided, however, that prior to the expiration of the Restricted Period, transfers and exchanges of beneficial interests in the Regulation S Global Note may be made pursuant to such restrictions only (1) to a Person that is not a U.S. person or for the account or benefit of a Person that is not a U.S. person within the meaning of Regulation S under the Securities Act or (2) to a QIB, in each case that hold such interests through Euroclear or Clearstream.

(e) If Notes are issued upon the registration of transfer, exchange or replacement of Notes not bearing the Restricted Notes Legend, the Notes so issued shall not bear such legend. If Notes are issued upon the registration or transfer, exchange or replacement of Notes bearing the Restricted Notes Legend, or if a request is made to remove the Restricted Notes Legend on a Note, the Notes so issued shall bear the Restricted Notes Legend, or the Restricted Notes Legend shall not be removed, as the case may be, unless there is delivered to the Partnership such satisfactory evidence, which may include an opinion of counsel of recognized standing licensed to practice law in the State of New York and experienced in matters involving the Securities Act, as may be reasonably required by the Partnership that neither the Restricted Notes Legend nor the restrictions on transfer set forth therein are required to ensure that transfers thereof comply with the provisions of Rule 144A, Rule 144 or Regulation S, that such Notes are not “restricted securities” within the meaning of Rule 144 or that such Notes were transferred pursuant to an effective registration statement under the Securities Act. Upon provision of such satisfactory evidence, the Trustee, at the direction of the Partnership, shall authenticate and deliver a Note that does not bear the Restricted Notes Legend. If a Restricted Notes Legend is removed from the face of a Note and the Note is subsequently held by an Affiliate of the Partnership, the Restricted Notes Legend shall be reinstated.

(f) Neither the Trustee nor the Registrar shall have any obligation or duty to monitor, determine or inquire as to compliance with any restrictions on transfer imposed under this Supplemental Indenture or under applicable law with respect to any transfer of any interest in any Note (including any transfers between or among Depositary participants or beneficial owners of interests in any Global Note) other than to require delivery of such certificates and other documentation or evidence as are expressly required by, and to do so only if and when expressly required by the terms of, this Supplemental Indenture, and to examine the same to determine

9

substantial compliance as to form with the express requirements hereof. Notwithstanding anything herein to the contrary, neither the Trustee nor the Registrar shall have any responsibility to receive any letters, opinions or certifications, nor any responsibility to monitor compliance with any transfer restrictions, in connection with any transfer or exchange of any beneficial interest in a Global Note for a beneficial interest in the same Global Note.

(g) Notwithstanding the foregoing, in the event that any Transfer Restricted Notes are exchanged for Exchange Notes in connection with an effective registration statement pursuant to the Registration Rights Agreement, the Partnership shall issue and, at the direction of the Partnership, the Trustee shall authenticate the Exchange Notes in exchange for Transfer Restricted Notes accepted for exchange in the exchange offer, which Exchange Notes shall not bear the Restricted Notes Legend, and the Registrar shall rescind any restriction on the transfer of such Exchange Notes.

Section 7. Form of Notes/Legends.

(a) The Notes are being offered only to (A) Persons reasonably believed to be QIBs in reliance on Rule 144A and (B) non-U.S. persons in reliance on Regulation S. Such Notes may thereafter be transferred to, among others, QIBs, and purchasers in reliance on Regulation S, in each case, in accordance with the procedures described herein. Exchange Notes exchanged for interests in the Rule 144A Notes and the Regulation S Notes will be issued in the form of permanent global notes deposited with the Trustee as hereinafter provided, including the appropriate legend set forth in the form of security attached as Exhibit A (the “Exchange Global Notes”). The Exchange Global Notes will be deposited upon issuance with, or on behalf of, the Trustee as custodian for the Depositary, duly executed by the Partnership and authenticated by the Trustee as hereinafter provided. The Exchange Global Notes may be represented by more than one certificate, if so required by the Depositary’s rules regarding the maximum principal amount to be represented by a single certificate.

(b) The Notes offered to QIBs in the United States of America in reliance on Rule 144A (the “Rule 144A Notes”) shall be issued in the form of a permanent global note including appropriate legends as set forth in the form of security attached as Exhibit A (the “Rule 144A Global Notes”), deposited with the Trustee, as custodian for the Depositary, duly executed by the Partnership and authenticated by the Trustee as hereinafter provided. The Rule 144A Global Notes may be represented by more than one certificate, if so required by the Depositary’s rules regarding the maximum principal amount to be represented by a single certificate. The aggregate principal amount of the Rule 144A Global Notes may from time to time be increased or decreased by adjustments made on the records of the Trustee, as custodian for the Depositary, or its nominee, as hereinafter provided.

(c) The Notes offered to non-U.S. persons outside the United States of America (the “Regulation S Notes”) in reliance on Regulation S shall be issued in the form of a permanent global note including appropriate legends as set forth in the form of security attached as Exhibit A (the “Regulation S Global Notes” and, together with the Rule 144A Global Notes and the Exchange Global Notes, the “Global Notes”). Each Regulation S Global Note will be deposited upon issuance with, or on behalf of, the Trustee as custodian for the Depositary. Prior

10

to the 40th day after the date the Notes are issued (such period through and including such 40th day, the “Restricted Period”), interests in the Regulation S Global Notes may only be transferred to non-U.S. persons pursuant to Regulation S, unless exchanged for interests in a Global Note in accordance with the transfer and certification requirements described herein. Investors may hold their interests in the Regulation S Global Note through organizations other than Euroclear or Clearstream that are participants in the Depositary’s system or directly through Euroclear or Clearstream, if they are participants in such systems, or indirectly through organizations which are participants in such systems. If such interests are held through Euroclear or Clearstream, Euroclear and Clearstream will hold such interests in the applicable Regulation S Global Note on behalf of their participants through customers’ securities accounts in their respective names on the books of their respective depositaries. Such depositaries, in turn, will hold such interests in the applicable Regulation S Global Note in customers’ securities accounts in the depositaries’ names on the books of the Depositary. The Regulation S Global Notes may be represented by more than one certificate, if so required by the Depositary’s rules regarding the maximum principal amount to be represented by a single certificate. The aggregate principal amount of the Regulation S Global Notes may from time to time be increased or decreased by adjustments made on the records of the Trustee, as custodian for the Depositary or its nominee, as hereinafter provided.

(d) Unless and until (i) a Note issued as a Transfer Restricted Note is sold under an effective registration statement, (ii) a Note issued as a Transfer Restricted Note is exchanged for an Exchange Note in connection with an effective registration statement pursuant to the Registration Rights Agreement or (iii) the Partnership receives an opinion of counsel satisfactory to it to the effect that neither such legend nor the related restrictions on transfer are required in order to maintain compliance with the provisions of the Securities Act:

(1) each Transfer Restricted Note shall bear the following legend on the face thereof (the “Restricted Notes Legend”):

THIS NOTE HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”), AND MAY NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED EXCEPT IN ACCORDANCE WITH THE FOLLOWING SENTENCE. BY ITS ACQUISITION HEREOF OR OF A BENEFICIAL INTEREST HEREIN, THE ACQUIRER (1) REPRESENTS THAT (A) IT AND ANY ACCOUNT FOR WHICH IT IS ACTING IS A “QUALIFIED INSTITUTIONAL BUYER” (WITHIN THE MEANING OF RULE 144A UNDER THE SECURITIES ACT) AND THAT IT EXERCISES SOLE INVESTMENT DISCRETION WITH RESPECT TO EACH SUCH ACCOUNT, OR (B) IT IS NOT A “U.S. PERSON” (WITHIN THE MEANING OF REGULATION S UNDER THE SECURITIES ACT) AND (2) AGREES FOR THE BENEFIT OF MPLX LP THAT IT WILL NOT OFFER, SELL, PLEDGE OR OTHERWISE TRANSFER THIS NOTE OR ANY BENEFICIAL INTEREST HEREIN, EXCEPT IN ACCORDANCE WITH THE SECURITIES ACT AND ANY APPLICABLE SECURITIES LAWS OF ANY STATE OF THE UNITED STATES AND ONLY (A) TO MPLX LP, (B) PURSUANT TO A REGISTRATION STATEMENT WHICH HAS BECOME EFFECTIVE UNDER THE SECURITIES ACT, (C) TO A QUALIFIED INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A UNDER THE SECURITIES ACT, (D) IN AN OFFSHORE TRANSACTION IN COMPLIANCE WITH RULE 904 OF REGULATION S UNDER THE SECURITIES ACT, OR (E) PURSUANT TO AN EXEMPTION FROM REGISTRATION PROVIDED BY RULE 144 UNDER THE SECURITIES ACT OR ANY OTHER AVAILABLE EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.

11

PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (2)(C) ABOVE OR (2)(D) ABOVE, A DULY COMPLETED AND SIGNED CERTIFICATE (THE FORM OF WHICH MAY BE OBTAINED FROM THE TRUSTEE) MUST BE DELIVERED TO THE TRUSTEE. PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (E) ABOVE, MPLX LP RESERVES THE RIGHT TO REQUIRE THE DELIVERY OF SUCH LEGAL OPINIONS, CERTIFICATIONS OR OTHER EVIDENCE AS MAY REASONABLY BE REQUIRED IN ORDER TO DETERMINE THAT THE PROPOSED TRANSFER IS BEING MADE IN COMPLIANCE WITH THE SECURITIES ACT AND APPLICABLE STATE SECURITIES LAWS. NO REPRESENTATION IS MADE AS TO THE AVAILABILITY OF ANY RULE 144 EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.

(2) each Global Note shall bear the following legend on the face thereof:

UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (“DTC”), NEW YORK, NEW YORK, TO THE PARTNERSHIP OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO., OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

TRANSFERS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS IN WHOLE, BUT NOT IN PART, TO NOMINEES OF DTC OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR’S NOMINEE AND TRANSFERS OF PORTIONS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN THE INDENTURE REFERRED TO HEREIN.

Section 8. Effect of Supplemental Indenture. The provisions of this Supplemental Indenture are intended to supplement those of the Indenture as in effect immediately prior to the execution and delivery hereof. The Indenture shall remain in full force and effect except to the extent that the provisions of the Indenture are expressly modified by the terms of this Supplemental Indenture.

12

Section 9. Governing Law. This Supplemental Indenture and the Notes shall be governed by and construed in accordance with the law of the State of New York, without giving effect to any principles of conflicts of laws thereunder to the extent the application of the laws of another jurisdiction would be required thereby.

Section 10. Trustee Not Responsible for Recitals or Issuance of Notes. The recitals and statements contained herein shall be taken as statements of the Partnership, and the Trustee assumes no responsibility for their correctness. The Trustee makes no representations as to the validity or sufficiency of this Supplemental Indenture or of the Notes other than with respect to the Trustee’s execution of this Supplemental Indenture and authentication of the Notes. The Trustee shall not be accountable for the use or application by the Partnership of the Notes or the proceeds thereof.

Section 11. Conflict with the TIA. If any provision hereof limits, qualifies or conflicts with a provision of the TIA that is required under the TIA to be a part of and govern this Supplemental Indenture, the latter provision shall control. If any provision of this Supplemental Indenture modifies or excludes any provision of the TIA that may be so modified or excluded, the latter provision shall be deemed to apply to this Supplemental Indenture as so modified or to be excluded, as the case may be.

Section 12. Counterparts. This Supplemental Indenture may be executed in any number of counterparts, each of which shall be an original; but such counterparts shall together constitute one and the same instrument. The exchange of copies of this Supplemental Indenture and of signature pages by facsimile or electronic (i.e., “pdf” or “tif”) transmission shall constitute effective execution and delivery of this Supplemental Indenture for all purposes. Signatures of the parties hereto transmitted by facsimile or electronic (i.e., “pdf” or “tif”) transmission shall be deemed to be their original signatures for all purposes of the Supplemental Indenture as to the parties hereto and may be used in lieu of the original.

[The remainder of this page is left blank intentionally]

13

IN WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture to be duly executed as of the day and year first above written.

[Signature Page to Twenty-First Supplemental Indenture]

[Signature Page to Twenty-First Supplemental Indenture]

Exhibit A

MPLX LP

4.250% Senior Notes due 2027

[FOR GLOBAL NOTES: UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (“DTC”), NEW YORK, NEW YORK, TO THE PARTNERSHIP OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO., OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

TRANSFERS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS IN WHOLE, BUT NOT IN PART, TO NOMINEES OF DTC OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR’S NOMINEE AND TRANSFERS OF PORTIONS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN THE INDENTURE REFERRED TO HEREIN.]

[FOR TRANSFER RESTRICTED NOTES: THIS NOTE HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”), AND MAY NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED EXCEPT IN ACCORDANCE WITH THE FOLLOWING SENTENCE. BY ITS ACQUISITION HEREOF OR OF A BENEFICIAL INTEREST HEREIN, THE ACQUIRER (1) REPRESENTS THAT (A) IT AND ANY ACCOUNT FOR WHICH IT IS ACTING IS A “QUALIFIED INSTITUTIONAL BUYER” (WITHIN THE MEANING OF RULE 144A UNDER THE SECURITIES ACT) AND THAT IT EXERCISES SOLE INVESTMENT DISCRETION WITH RESPECT TO EACH SUCH ACCOUNT, OR (B) IT IS NOT A “U.S. PERSON” (WITHIN THE MEANING OF REGULATION S UNDER THE SECURITIES ACT) AND (2) AGREES FOR THE BENEFIT OF MPLX LP THAT IT WILL NOT OFFER, SELL, PLEDGE OR OTHERWISE TRANSFER THIS NOTE OR ANY BENEFICIAL INTEREST HEREIN, EXCEPT IN ACCORDANCE WITH THE SECURITIES ACT

AND ANY APPLICABLE SECURITIES LAWS OF ANY STATE OF THE UNITED STATES AND ONLY (A) TO MPLX LP, (B) PURSUANT TO A REGISTRATION STATEMENT WHICH HAS BECOME EFFECTIVE UNDER THE SECURITIES ACT, (C) TO A QUALIFIED INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A UNDER THE SECURITIES ACT, (D) IN AN OFFSHORE TRANSACTION IN COMPLIANCE WITH RULE 904 OF REGULATION S UNDER THE SECURITIES ACT, OR (E) PURSUANT TO AN EXEMPTION FROM REGISTRATION PROVIDED BY RULE 144 UNDER THE SECURITIES ACT OR ANY OTHER AVAILABLE EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.

PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (2)(C) ABOVE OR (2)(D) ABOVE, A DULY COMPLETED AND SIGNED CERTIFICATE (THE FORM OF WHICH MAY BE OBTAINED FROM THE TRUSTEE) MUST BE DELIVERED TO THE TRUSTEE. PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (E) ABOVE, MPLX LP RESERVES THE RIGHT TO REQUIRE THE DELIVERY OF SUCH LEGAL OPINIONS, CERTIFICATIONS OR OTHER EVIDENCE AS MAY REASONABLY BE REQUIRED IN ORDER TO DETERMINE THAT THE PROPOSED TRANSFER IS BEING MADE IN COMPLIANCE WITH THE SECURITIES ACT AND APPLICABLE STATE SECURITIES LAWS. NO REPRESENTATION IS MADE AS TO THE AVAILABILITY OF ANY RULE 144 EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.]

MPLX LP, a limited partnership duly formed and existing under the laws of the State of Delaware (herein called the “Partnership,” which term includes any successor Person under the Indenture hereinafter referred to), for value received, hereby promises to pay to [•] [Insert if Global Security: CEDE & CO.], or registered assigns, the principal sum of [•] Dollars ($[•]) [Insert if Global Security: , or such greater or lesser amount as indicated on the Schedule of Increases or Decreases in the Principal Amount of Securities attached hereto,] on December 1, 2027, and to pay interest thereon from June 1, 2019 or from the most recent Interest Payment Date to which interest has been paid or duly provided for, semi-annually on June 1 and December 1 in each year commencing December 1, 2019, at the rate of 4.250% per annum, until the principal hereof is paid or made available for payment. Interest on the Notes will be paid on the basis of a 360-day year consisting of twelve 30-day months. The Partnership shall pay Additional Interest, if any, on the applicable Interest Payment Date in the same manner as interest is paid on the Notes and in the amounts set forth in the Registration Rights Agreement. The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date will, as provided in such Indenture, be paid to the Person in whose name this Debt Security (or one or more Predecessor Securities) is registered at the close of business on the Regular Record Date for such interest, which shall be May 15 or November 15 (whether or not a Business Day), as the case may be, next preceding such Interest Payment Date. Any such interest not so punctually paid or duly provided for will forthwith cease to be payable to the Holder on such Regular Record Date and may either be paid to the Person in whose

name this Debt Security (or one or more Predecessor Securities) is registered at the close of business on a Special Record Date for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Debt Securities of this series not less than 10 days prior to such Special Record Date, or be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange on which the Debt Securities of this series may be listed, and upon such notice as may be required by such exchange all as more fully provided in said Indenture. If an Interest Payment Date, a Stated Maturity or a Redemption Date with respect to this Debt Security falls on a day that is not a Business Day, the payment will be made on the next Business Day and no interest will accrue for the period from and after such Interest Payment Date, Stated Maturity or Redemption Date.

Payment of the principal of (and premium, if any) and interest on this Debt Security will be made at the office or agency of the Partnership maintained for that purpose in New York, New York, in such coin or currency of the United States of America as at the time of payment is legal tender for payment of public and private debts; provided, however, that (1) payments on any Global Security shall be made by electronic (same-day) funds transfer to the Depositary and (2) at the option of the Partnership payment of interest may be made by check mailed to the address of the Person entitled thereto as such address shall appear in the Debt Security Register or by electronic funds transfer to an account maintained by the Person entitled thereto as specified in the Debt Security Register, provided that such Person shall have given the Trustee written instructions.

Reference is hereby made to the further provisions of this Debt Security set forth on the reverse hereof, which further provisions shall for all purposes have the same effect as if set forth at this place.

Unless the certificate of authentication hereon has been executed by the Trustee referred to on the reverse hereof by manual signature, this Debt Security shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose.

IN WITNESS WHEREOF, the Partnership has caused this instrument to be duly executed.

Dated:

CERTIFICATE OF AUTHENTICATION

This is one of the Debt Securities of the series designated therein referred to in the within-mentioned Indenture.

Dated:

MPLX LP

4.250% Senior Notes due 2027

This Security is one of a duly authorized issue of Debt Securities of the Partnership (herein called the “Securities”), issued and to be issued in one or more series under a Senior Indenture, dated as of February 12, 2015, as amended or supplemented to date, including as amended and supplemented by the Twenty-First Supplemental Indenture, dated as of September 23, 2019 (herein called the “Indenture,” which term shall have the meaning assigned to it in such instrument), between the Partnership and The Bank of New York Mellon Trust Company, N.A., as Trustee (herein called the “Trustee,” which term includes any successor trustee under the Indenture), and reference is hereby made to the Indenture for a statement of the respective rights, limitations of rights, duties and immunities thereunder of the Partnership, the Trustee and the Holders of the Securities and of the terms upon which the Securities are, and are to be, authenticated and delivered. This Security is one of the series designated on the face hereof initially limited in aggregate principal amount to $[•].

Prior to September 1, 2027, the Securities are subject to redemption, in whole at any time or in part from time to time, at the election of the Partnership, at a redemption price equal to the greater of (1) 100% of the principal amount of such Securities to be redeemed or (2) the sum of the present values of the remaining scheduled payments of principal and interest on the Securities to be redeemed that would be due if such Securities matured on September 1, 2027 (exclusive of interest accrued to the Redemption Date) discounted to the Redemption Date on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the then current Treasury Rate plus 30 basis points, plus, in either case, accrued and unpaid interest on the principal amount being redeemed to, but not including, the Redemption Date.

On or after September 1, 2027, the Securities are subject to redemption, in whole at any time or in part from time to time, at the election of the Partnership, at a redemption price equal to 100% of the principal amount of such Securities to be redeemed plus accrued and unpaid interest on the principal amount being redeemed to, but not including, the Redemption Date.

For purposes of the redemption provisions of the Securities, the following terms are applicable:    

“Business Day” means any Monday, Tuesday, Wednesday, Thursday or Friday that is not a day on which banking institutions in New York, New York are authorized or obligated by law or executive order to close. If a payment date is not a Business Day at a Place of Payment, payment may be made at that place on the next succeeding day that is a Business Day, and no interest shall accrue for the intervening period.

“Comparable Treasury Issue” means the United States Treasury security selected, in accordance with customary financial practice, by an Independent Investment Banker as having a maturity comparable to the remaining term of the Securities (assuming for this purpose that the Securities matured on September 1, 2027) (the “Remaining Life”) to be redeemed that would be utilized, at the time of selection and in accordance with customary financial practice, in pricing new issues of corporate debt securities of comparable maturity to the remaining term of such Securities (assuming that the Securities matured on September 1, 2027).

“Comparable Treasury Price” means, with respect to any Redemption Date, (1) the average, as determined by the Partnership, of the Reference Treasury Dealer Quotations for such Redemption Date, after excluding the highest and lowest Reference Treasury Dealer Quotations, or (2) if the Partnership obtains fewer than four such Reference Treasury Dealer Quotations, the average of all such quotations.

“Independent Investment Banker” means one of the Reference Treasury Dealers that the Partnership appoints to act as the Independent Investment Banker from time to time.

“Reference Treasury Dealer” means at least four primary U.S. Government securities dealers in The City of New York as the Partnership shall select.

“Reference Treasury Dealer Quotations” means, with respect to each Reference Treasury Dealer and any Redemption Date, the average, as determined by the Partnership, of the bid and asked prices for the Comparable Treasury Issue (expressed in each case as a percentage of its principal amount) quoted in writing to the Partnership by such Reference Treasury Dealer at 3:30 p.m., New York City time, on the third Business Day preceding such Redemption Date.

“Treasury Rate” means, as of any Redemption Date, the rate per year equal to: (1) the yield, under the heading which represents the average for the immediately preceding week, appearing in, or available through, the most recently published statistical release designated “H.15” or any successor publication which is published weekly by the Board of Governors of the Federal Reserve System (or companion online data resource published by the Board of Governors of the Federal Reserve System) and which established yields on actively traded United States Treasury securities adjusted to constant maturity under the caption “Treasury Constant Maturities,” for the maturity corresponding to the applicable Comparable Treasury Issue; provided that, if no maturity is within three months before or after the Remaining Life of the Notes to be redeemed, yields for the two published maturities most closely corresponding to the applicable Comparable Treasury Issue will be determined and the Treasury Rate will be interpolated or extrapolated from such yields on a straight line basis, rounding to the nearest month; or (2) if such release (or any successor release) is not published during the week preceding the calculation date or does not contain such yields, the rate per year equal to the semi-annual equivalent yield to maturity of the applicable Comparable Treasury Issue, calculated using a price for the applicable Comparable Treasury Issue (expressed as a percentage of its principal amount) equal to the related Comparable Treasury Price for such Redemption Date. The Treasury Rate will be calculated by the Partnership on the third Business Day preceding the Redemption Date.

Notice of the redemption will be transmitted to holders of Securities at least 10 and not more than 60 days prior to the Redemption Date. If fewer than all of the Securities are to be redeemed, the Trustee will select the particular Securities or portions thereof for redemption from the outstanding Securities not previously called by any of the following methods: (i) in compliance with the requirements of the principal national securities exchange, if any, on which such Securities are listed, (2) on a pro rata basis to the extent practicable and in accordance with the procedures of the Depositary or (3) by lot or in such other similar method in accordance with the procedures of the depositary of such Securities.

Unless the Partnership defaults in payment of the redemption price, on or after the Redemption Date, interest will cease to accrue on the Securities or portions thereof called for redemption.

In the event of redemption of this Security in part only, a new Security or Securities of this series and of like tenor for the unredeemed portion hereof will be issued in the name of the Holder hereof upon the cancellation hereof.

The Indenture contains provisions for defeasance at any time of the entire indebtedness of this Security or of certain restrictive covenants and Events of Default with respect to this Security, in each case upon compliance with certain conditions set forth in the Indenture.

The Indenture contains provisions permitting the Partnership and the Trustee to modify the Indenture or any supplemental indenture without the consent of the Holders for one or more of the following purposes: (1) to evidence the succession of another Person to the Partnership; (2) to surrender any right or power conferred by the Indenture, to add to the covenants for the protection of the Holders of the Securities or to add additional defaults or events of default; (3) to cure any ambiguity, to correct or supplement any provision of the Indenture which may be defective or inconsistent with any other provision of the Indenture, or to make any other provisions with respect to matters or questions arising under the Indenture as shall not adversely affect the interests of the Holders; (4) to permit qualification of the Indenture or any supplemental indenture under the TIA; (5) to permit or facilitate the issuance of Debt Securities of any series in uncertificated form; (6) to secure any or all Debt Securities; (7) to make any change that does not adversely affect the rights of any Holder; (8) to add to, change or eliminate any of the provisions of the Indenture in respect of one or more Debt Securities, under certain conditions specified therein; (9) to evidence and provide acceptance of appointment thereunder by a successor or separate Trustee and to add to or change the provisions under the Indenture as necessary; and (10) to establish the form or terms of Debt Securities of a particular series as permitted by Sections 2.01 and 2.03 of the Indenture.

The Indenture also permits, with certain exceptions as therein provided, the amendment thereof and the modification of the rights and obligations of the Partnership and the rights of the Holders of the Securities of each series to be affected under the Indenture at any time by the Partnership and the Trustee with the consent of the Holders of not less than a majority in aggregate principal amount of the Securities at the time

Outstanding of each series to be affected. The Indenture also contains provisions permitting the Holders of at least a majority in aggregate principal amount of the Securities at the time Outstanding, on behalf of the Holders of all Securities, to waive compliance by the Partnership with certain provisions of the Indenture and certain past defaults under the Indenture and their consequences. Any such consent or waiver by the Holder of this Security shall be conclusive and binding upon such Holder and upon all future Holders of this Security and of any Security issued upon the registration of transfer hereof or in exchange herefor or in lieu hereof, whether or not notation of such consent or waiver is made upon this Security.

As provided in and subject to the provisions of the Indenture, the Holder of this Security shall not have the right to institute any proceeding with respect to the Indenture or for the appointment of a receiver or trustee or for any other remedy thereunder, unless such Holder shall have previously given the Trustee written notice of a continuing Event of Default with respect to the Securities, the Holders of not less than 25% in aggregate principal amount of the Securities then Outstanding shall have made written request to the Trustee to institute proceedings in respect of such Event of Default as Trustee and offered the Trustee indemnity, and the Trustee shall not have received from the Holders of a majority in principal amount of the Securities then Outstanding a direction inconsistent with such request, and shall have failed to institute any such proceeding, for 60 days after receipt of such notice, request and offer of indemnity. The foregoing shall not apply to any suit instituted by the Holder of this Security for the enforcement of any payment of principal hereof or any premium or interest hereon on or after the respective due dates expressed herein.

No reference herein to the Indenture and no provision of this Security or of the Indenture shall alter or impair the obligation of the Partnership, which is absolute and unconditional, to pay the principal of and any premium and interest on this Security at the times, place and rate, and in the coin or currency, herein prescribed.

As provided in the Indenture and subject to certain limitations therein set forth, the transfer of this Security is registrable in the Debt Security Register, upon surrender of this Security for registration of transfer at the office or agency of the Partnership in any place where the principal of and any premium and interest on this Security are payable, duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Partnership and the Registrar duly executed by, the Holder hereof or his attorney duly authorized in writing, and thereupon one or more new Securities and of like tenor, of authorized denominations and for the same aggregate principal amount, will be issued to the designated transferee or transferees.

The Securities are issuable only in registered form without coupons in denominations of $2,000 and integral multiples of $1,000 in excess thereof. As provided in the Indenture and subject to certain limitations therein set forth, the Securities are exchangeable for a like aggregate principal amount of Securities and of like tenor of a different authorized denomination, as requested by the Holder surrendering the same.

No service charge shall be made for any such registration of transfer or exchange, but, subject to any applicable provisions of the Indenture, the Partnership may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection therewith.

Prior to due presentment of this Security for registration of transfer, the Partnership, the Trustee and any agent of the Partnership or the Trustee may treat the Person in whose name this Security is registered as the owner hereof for all purposes, whether or not this Security be overdue, and neither the Partnership, the Trustee nor any such agent shall be affected by notice to the contrary.

All terms used in this Security which are defined in the Indenture shall have the meaning assigned to them in the Indenture.

FORM OF ASSIGNMENT

ABBREVIATIONS

Customary abbreviations may be used in the name of a Securityholder or an assignee, such as TEN COM (=tenants in common), TEN ENT (=tenants by the entireties), JT TEN (=joint tenants with rights of survivorship and not as tenants in common), CUST (=custodian), and U/G/M/A (=Uniform Gift to Minors Act).

Additional abbreviations may also be used though not in the above list.

FOR VALUE RECEIVED, the undersigned hereby sell(s),

assign(s) and transfer(s) unto

Please insert Social Security or

other identifying number of assignee

PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING POSTAL ZIP CODE, OF ASSIGNEE

the within Security and all rights thereunder, hereby irrevocably constituting and appointing                                           attorney to transfer said Security on the books of the Partnership, with full power of substitution in the premises.

EXHIBIT B

FORM OF CERTIFICATE TO BE DELIVERED UPON EXCHANGE OR REGISTRATION OF TRANSFER OF NOTES

Re: 4.250% Senior Notes due 2027 (the “Notes”) of MPLX LP (the “Partnership”)

This Certificate relates to $                     principal amount of Notes held in book-entry or definitive form by (the “Transferor”). The Transferor has requested the Registrar by written order to exchange or register the transfer of a Note or Notes or beneficial interests therein (the “Transfer”).

In connection with such request and in respect of each such Note or beneficial interest therein, the Transferor does hereby certify that the Transferor is familiar with the Indenture relating to the above-captioned Notes and that the Transfer does not require registration under the Securities Act of 1933, as amended (the “Securities Act”), because:

Fill in blank or check appropriate item, as applicable.

EXHIBIT C

FORM OF CERTIFICATE TO BE DELIVERED IN CONNECTION WITH TRANSFERS

PURSUANT TO REGULATION S

Re: 4.250% Senior Notes due 2027 (the “Notes”) of MPLX LP (the “Partnership”)

This Certificate relates to $                      principal amount of Notes held in book-entry form by (the “Transferor”).

The Transferor has requested the Registrar by written order to exchange or register the transfer of a Note or Notes or beneficial interests therein (the “Transfer”) for an interest in the Regulation S Temporary Global Note to be held with [Euroclear] [Clearstream] through the Depositary (in each case as defined in the Indenture related to the above-referenced Notes).

In connection with such request and in respect of each such Note or beneficial interest therein, the Transferor does hereby certify that the Transferor is familiar with such Indenture and Establishment Action and that:

(a) the offer of such Notes or beneficial interests was not made to a person in the United States or for the benefit of a person in the United States (other than an Initial Purchaser);

(b) at the time the buy order was originated, the transferee was outside the United States or the Transferor and any person acting on its behalf reasonably believed that the transferee was outside the United States; or the transaction was executed in, on or through the facilities of a designated offshore securities market and neither the Transferor nor any person acting on its behalf knows that the transaction was prearranged with a buyer in the United States;

(c) no directed selling efforts have been made by the Transferor in the United States in contravention of the requirements of Rule 903(a) or Rule 904(a) of Regulation S under the U.S. Securities Act of 1933, as amended (the “Securities Act”), as applicable;

(d) the transaction is not part of a plan or scheme to evade the registration requirements of the Securities Act; and

(e) if the proposed transfer is being made prior to the expiration of a 40-day “distribution compliance period” as defined in Regulation S under the Securities Act, the transfer is being made (a) to a person that is not a U.S. person or for the account or benefit of a person that is not a U.S. person within the meaning of Regulation S under the Securities Act; or (b) to a “qualified institutional buyer” within the meaning of Rule 144A under the Securities Act, in each case that holds such Note or beneficial interests through [Euroclear] [Clearstream].

EXHIBIT 4.6

TWENTY-SECOND SUPPLEMENTAL INDENTURE

THIS TWENTY-SECOND SUPPLEMENTAL INDENTURE, dated as of September 23, 2019 (this “Supplemental Indenture”), is between MPLX LP, a limited partnership duly formed and existing under the laws of the State of Delaware (the “Partnership”), and The Bank of New York Mellon Trust Company, N.A., a national banking association, as trustee (the “Trustee”).

WITNESSETH

WHEREAS, pursuant to the Senior Indenture, dated as of February 12, 2015 (the “Base Indenture”), as supplemented by the First Supplemental Indenture, dated as of February 12, 2015, the Second Supplemental Indenture, dated as of December 22, 2015, the Third Supplemental Indenture, dated as of December 22, 2015, the Fourth Supplemental Indenture, dated as of December 22, 2015, the Fifth Supplemental Indenture, dated as of December 22, 2015, the Sixth Supplemental Indenture, dated as of February 10, 2017, the Seventh Supplemental Indenture, dated as of February 10, 2017, the Eighth Supplemental Indenture, dated as of February 8, 2018, the Ninth Supplemental Indenture, dated as of February 8, 2018, the Tenth Supplemental Indenture, dated as of February 8, 2018, the Eleventh Supplemental Indenture, dated as of February 8, 2018, the Twelfth Supplemental Indenture, dated as of February 8, 2018, the Thirteenth Supplemental Indenture, dated as of November 15, 2018, the Fourteenth Supplemental Indenture, dated as of November 15, 2018, the Fifteenth Supplemental Indenture, dated as of September 9, 2019, the Sixteenth Supplemental Indenture, dated as of September 9, 2019, the Seventeenth Supplemental Indenture, dated as of September 23, 2019, the Eighteenth Supplemental Indenture, dated as of September 23, 2019, the Nineteenth Supplemental Indenture, dated as of September 23, 2019, the Twentieth Supplemental Indenture, dated as of September 23, 2019, and the Twenty-First Supplemental Indenture, dated as of September 23, 2019 (as so supplemented, the “Indenture”), in each case between the Partnership and the Trustee, the Partnership may from time to time issue and sell Debt Securities in one or more series;

WHEREAS, the Partnership desires to create and authorize a new series of Debt Securities entitled “5.200% Senior Notes due 2047” (the “Notes”), limited initially to $487,188,000 in aggregate principal amount, and to provide the terms and conditions upon which the Notes are to be executed, registered, authenticated, issued and delivered, the Partnership has duly authorized the execution and delivery of this Supplemental Indenture;

WHEREAS, the Notes are a series of Debt Securities and are being issued under the Indenture, as supplemented by this Supplemental Indenture, and are subject to the terms contained therein and herein;

WHEREAS, the Notes are to be substantially in the form attached hereto as Exhibit A; and

WHEREAS, all acts and things necessary to make the Notes, when executed by the Partnership and authenticated and delivered by or on behalf of the Trustee as provided in the Indenture and this Supplemental Indenture, the valid, binding and legal obligations of the Partnership, and to make this Supplemental Indenture a legal, binding and enforceable agreement, have been done and performed.

NOW, THEREFORE, in order to declare the terms and conditions upon which the Notes are executed, registered, authenticated, issued and delivered, and in consideration of the foregoing premises and the purchase of such Notes by the Holders thereof, the Partnership and the Trustee mutually covenant and agree, for the equal and proportionate benefit of the Holders from time to time of the Notes, as follows:

Section 1. Definitions. Terms used in this Supplemental Indenture and not defined herein shall have the respective meanings given such terms in the Indenture.

Section 2. Other Definitions. In addition, the following terms shall have the following meanings with respect to the Notes:

“Additional Interest” means “Additional Interest” payable pursuant to the Registration Rights Agreement.

“Board Resolution” means a copy of a resolution or resolutions of the Board of Directors, certified by the Secretary or an Assistant Secretary of the General Partner to be in full force and effect on the date of such certification, and delivered to the Trustee.

“Clearstream” means Clearstream Banking, société anonyme, or any successor securities clearing agency.

“Consolidated Net Tangible Assets” means the aggregate value of all assets of the Partnership and its Subsidiaries after deducting therefrom: (i) all current liabilities, excluding all short-term indebtedness and the current portion of long-term indebtedness; (ii) all investments in unconsolidated subsidiaries and all investments accounted for on the equity basis; and (iii) all goodwill patents and trademarks, unamortized debt discounts and other similar intangibles (all determined in conformity with generally accepted accounting principles and calculated on a basis consistent with the Partnership’s most recent audited consolidated financial statements).

“Euroclear” means Euroclear Bank S.A./N.V., as operator of Euroclear systems Clearance System or any successor securities clearing agency.

“Exchange Global Notes” has the meaning set forth in Section 7(a) herein.

“Exchange Notes” means any notes issued in exchange for Notes pursuant to the Registration Rights Agreement or similar agreement.

“Global Notes” has the meaning set forth in Section 7(c) herein.

“Interest Payment Date,” when used with respect to any installment of interest on any Debt Security, means the date specified in such Debt Security as the fixed date on which such installment of interest is due and payable.

2

“Mortgage” means as the context may require, (i) to mortgage, pledge, encumber or subject to a lien or (ii) a mortgage, pledge, encumbrance or lien.

“Predecessor Security” of any particular Debt Security means every previous Debt Security evidencing all or a portion of the same debt as that evidenced by such particular Debt Security; and, for the purposes of this definition, any Debt Security authenticated and delivered under Section 2.09 of the Base Indenture in exchange for or in lieu of a mutilated, destroyed, lost or stolen Debt Security shall be deemed to evidence the same debt as the mutilated, destroyed, lost or stolen Debt Security.

“QIB” means a “qualified institutional buyer” as defined in Rule 144A.

“Registration Rights Agreement” means the registration rights agreement, dated as of the date of this Supplemental Indenture, by and among the Partnership, the General Partner, Barclays Capital Inc., MUFG Securities Americas Inc. and Wells Fargo Securities, LLC.

“Regular Record Date” for the interest payable on any Interest Payment Date on the Debt Securities means the date specified for that purpose as contemplated by Section 2.03 of the Base Indenture.

“Regulation S” means Regulation S promulgated under the Securities Act.

“Regulation S Global Notes” has the meaning set forth in Section 7(c) herein.

“Regulation S Notes” has the meaning set forth in Section 7(c) herein.

“Restricted Notes Legend” has the meaning set forth in Section 7(d) herein.

“Restricted Period” has the meaning set forth in Section 7(c) herein.

“Rule 144” means Rule 144 promulgated under the Securities Act.

“Rule 144A” means Rule 144A promulgated under the Securities Act.

“Rule 144A Global Notes” has the meaning set forth in Section 7(b) herein.

“Rule 144A Notes” has the meaning set forth in Section 7(b) herein.

“Special Record Date” for the payment of any Defaulted Interest means a date fixed by the Trustee pursuant to Section 2.17 of the Base Indenture.

“Transfer Restricted Note” means any Note that bears or is required to bear the Restricted Notes Legend.

“U.S. person” means a “U.S. person” as defined in Regulation S.

3

Section 3. Creation and Authorization of Series.

(a) There is hereby created and authorized the following new series of Debt Securities to be issued under the Indenture, to be designated as the “5.200% Senior Notes due 2047.”

(b) The Notes shall be limited initially to $487,188,000 in aggregate principal amount. Notwithstanding the foregoing initial aggregate principal amount, the Partnership may, from time to time, without notice to or consent of the Holders of the Notes, increase the principal amount of the Notes that may be issued under this Supplemental Indenture and issue such increased principal amount (or any portion thereof), in which case any additional Notes so issued will have the same terms and conditions other than the public offering price, original interest accrual date and initial interest payment date, and the same CUSIP numbers as the applicable series of Notes previously issued, will be fungible with the applicable series of Notes previously issued for U.S. federal income tax purposes, and will carry the same right to receive accrued and unpaid interest as the Notes previously issued, and such additional notes will form a single series with the Notes of such series previously issued, including, without limitation, for purposes of waivers, amendments, redemptions and, if any, offers to purchase, and will rank equally and ratably with the Notes of such series previously issued.

(c) The date on which the principal is payable on the Notes, unless accelerated pursuant to the Indenture, shall be as provided in the form of security attached hereto as Exhibit A.

(d) The Notes shall bear interest as provided in the form of security attached hereto as Exhibit A. The Interest Payment Dates and the Regular Record Dates for the determination of Holders of the Notes to whom such interest is payable shall be as provided in the form of security attached hereto as Exhibit A. Additional Interest, if any, will be payable in arrears on each Interest Payment Date following accrual in the same manner as regular interest on the Notes.

(e) The Notes shall be redeemable at the option of the Partnership as set forth in the form of security attached hereto as Exhibit A.

(f) The provisions of Sections 3.04 and 3.05 of the Base Indenture shall not be applicable to the Notes.

(g) The Notes will be issued only in fully registered form, without coupons, in denominations provided herein and in the form of security attached hereto as Exhibit A.

(h) The Events of Default and covenants specified in the Indenture will apply to the Notes.

(i) The defeasance and covenant defeasance provisions of Article XI of the Indenture, including both Sections 11.02 and 11.03 of the Base Indenture, will apply to the Notes.

4

(j) The Notes shall be issued in the form of one or more Global Securities substantially in the form of security attached hereto as Exhibit A. The Partnership initially appoints The Depository Trust Company to act as Depositary with respect to the Notes. Additional provisions applicable to the Notes issued in the form of a Global Security are set forth in the form of security attached hereto as Exhibit A.

(k) The Notes shall be issuable only in denominations of $2,000 and integral multiples of $1,000 in excess thereof.

(l) The Trustee will initially act as the Registrar for the Notes and as the paying agent with respect to the Notes. The Place of Payment will be The Bank of New York Mellon Trust Company, N.A., 240 Greenwich Street, New York, New York 10286.

(m) Except as otherwise set forth herein and in the Notes, the terms of the Notes shall be as set forth in the Indenture, including those made part of the Indenture by reference to the TIA.

Section 4. Additional Covenants. In addition to the covenants set forth in Article IV of the Indenture, the following additional covenants shall apply with respect to the Notes:

Section 4.10 Mortgage of Certain Property.

If the Partnership or any Subsidiary of the Partnership shall Mortgage as security for any indebtedness for money borrowed any pipeline, terminal or other logistics or storage property or asset employed in the transportation, distribution, storage, terminalling, processing or marketing of crude oil, natural gas, condensate or refined products that (i) is located in the United States and (ii) is determined to be a principal property by the Board of Directors in its discretion, the Partnership will secure, or will cause such Subsidiary to secure, the Notes and all other Debt Securities equally and ratably with all indebtedness or obligations secured by the Mortgage then being given; provided, however, that this covenant shall not apply in the case of:

5

Notwithstanding the foregoing restriction contained in this Section 4.10, the Partnership may and may permit its Subsidiaries to incur liens or grant Mortgages on property covered by the restriction above so long as the net book value of the property so encumbered, together with all property subject to the restriction on sale and leasebacks contained in Section 4.11, does not, at the time such lien or Mortgage is granted, exceed fifteen percent (15%) of Consolidated Net Tangible Assets.

Section 4.11 Sale and Leaseback of Certain Properties.

The Partnership will not, nor will it permit any Subsidiary of the Partnership to, sell or transfer any pipeline, terminal or other logistics or storage property or asset employed in the transportation, distribution, storage, terminalling, processing or marketing of crude oil, natural gas, condensate or refined products that (i) is located in the United States and (ii) is determined to be a principal property by the Board of Directors in its discretion, with the intention of taking back a lease of such property; provided, however, this covenant shall not apply if:

6

In the event of such a sale or transfer, the Partnership shall deliver to the Trustee the Board Resolution referred to in the parenthetical phrase contained in subclause (4)(B) of this Section 4.11 and an Officer’s Certificate setting forth all material facts under this Section 4.11.

For the purposes of this Section 4.11, the term retirement of such funded debt shall include the “in substance defeasance” of such funded debt in accordance with then applicable accounting rules.

7

Section 5. Consolidation, Merger, Sale or Conveyance. With respect to the Notes, Section 10.01 of the Base Indenture shall be amended to include the following language at the end of such section:

For purposes of this Section 10.01, “substantially all of its assets” shall mean, at any date, a portion of the non-current assets reflected in the Partnership’s consolidated balance sheet as of the end of the most recent quarterly period that represents at least sixty-six and two-thirds percent (66 2/3%) of the total reported value of such assets.

(a) The initial offering and sale of the Notes shall not be registered under the Securities Act or any state securities laws. The Notes shall be offered pursuant to exemptions from the registration requirements of the Securities Act in reliance upon Rule 144A and Regulation S promulgated under the Securities Act. For so long as any of the Notes constitute “restricted securities” within the meaning of Rule 144(a)(3) promulgated under the Securities Act, the Partnership shall, if the Partnership is not then subject to the reporting requirements of Section 13 or 15(d) of the Exchange Act, furnish to any Holder or beneficial owner of such Notes, or to any prospective purchaser of such Notes designated by such Holder or beneficial owner, in each case upon the written request of such Holder, beneficial owner or prospective purchaser, the information required to be provided pursuant to Rule 144A(d)(4) promulgated under the Securities Act.

(b) The following provisions shall apply with respect to any proposed transfer of any Transfer Restricted Note prior to the expiration of the holding period applicable to sales of such Notes under Rule 144, and the Registrar shall refuse to register any transfer of such Notes not complying with the restrictions set forth in the Restricted Notes Legend and in this Section 6. In addition to the requirements set forth in Section 2.07 of the Base Indenture, Transfer Restricted Notes that are presented or surrendered for registration of transfer or exchange pursuant to Section 2.07 of the Base Indenture shall be accompanied by the following additional information and documents, as applicable, upon which the Registrar may conclusively rely:

(i) if such Transfer Restricted Notes are being delivered to the Registrar by a Holder for registration in the name of such Holder, without transfer, a certification from such Holder to that effect (in substantially the form of Exhibit B hereto);

(ii) if such Transfer Restricted Notes are being transferred (1) to a QIB in accordance with Rule 144A or (2) pursuant to an effective registration statement under the Securities Act, a certification to that effect from such Holder (in substantially the form of Exhibit B hereto);

(iii) if such Transfer Restricted Notes are being transferred pursuant to an exemption from registration in accordance with Rule 903 or Rule 904 of Regulation S, certifications to that effect from such Holder (in substantially the form of Exhibit B and Exhibit C hereto) and an opinion of counsel to that effect if the Partnership or the Trustee so requests; or

(iv) if such Transfer Restricted Notes are being transferred in reliance on and in compliance with (1) an exemption from registration in accordance with Rule 144 under the Securities Act or (2) another exemption from the registration requirements of the Securities Act, a certification to that effect from such Holder (in substantially the form of Exhibit B attached hereto) and an opinion of counsel, certification or other evidence as may reasonably be required to that effect if the Partnership or the Trustee so requests.

8

(c) A Holder of a beneficial interest in a Regulation S Global Note who wishes to transfer its interest in such Note to a QIB in accordance with Rule 144A who takes delivery in the form of a beneficial interest in the Rule 144A Global Note shall deliver to the Registrar a certification to that effect (in substantially the form of Exhibit B attached hereto) upon which the Registrar may conclusively rely. After the expiration of the Restricted Period, interests in the Regulation S Global Note may be transferred without requiring the certification set forth in this Section 6(c).

(d) The transfer and exchange of Global Notes or beneficial interests therein shall be effected through the Depositary, in accordance with Section 2.07 of the Base Indenture and Section 6 and Section 7 hereof (including the restrictions on transfer set forth therein and herein) and the rules and procedures of the Depositary therefor, which shall include restrictions on transfer comparable to those set forth therein and herein to the extent required by the Securities Act; provided, however, that prior to the expiration of the Restricted Period, transfers and exchanges of beneficial interests in the Regulation S Global Note may be made pursuant to such restrictions only (1) to a Person that is not a U.S. person or for the account or benefit of a Person that is not a U.S. person within the meaning of Regulation S under the Securities Act or (2) to a QIB, in each case that hold such interests through Euroclear or Clearstream.

(e) If Notes are issued upon the registration of transfer, exchange or replacement of Notes not bearing the Restricted Notes Legend, the Notes so issued shall not bear such legend. If Notes are issued upon the registration or transfer, exchange or replacement of Notes bearing the Restricted Notes Legend, or if a request is made to remove the Restricted Notes Legend on a Note, the Notes so issued shall bear the Restricted Notes Legend, or the Restricted Notes Legend shall not be removed, as the case may be, unless there is delivered to the Partnership such satisfactory evidence, which may include an opinion of counsel of recognized standing licensed to practice law in the State of New York and experienced in matters involving the Securities Act, as may be reasonably required by the Partnership that neither the Restricted Notes Legend nor the restrictions on transfer set forth therein are required to ensure that transfers thereof comply with the provisions of Rule 144A, Rule 144 or Regulation S, that such Notes are not “restricted securities” within the meaning of Rule 144 or that such Notes were transferred pursuant to an effective registration statement under the Securities Act. Upon provision of such satisfactory evidence, the Trustee, at the direction of the Partnership, shall authenticate and deliver a Note that does not bear the Restricted Notes Legend. If a Restricted Notes Legend is removed from the face of a Note and the Note is subsequently held by an Affiliate of the Partnership, the Restricted Notes Legend shall be reinstated.

(f) Neither the Trustee nor the Registrar shall have any obligation or duty to monitor, determine or inquire as to compliance with any restrictions on transfer imposed under this Supplemental Indenture or under applicable law with respect to any transfer of any interest in any Note (including any transfers between or among Depositary participants or beneficial owners of interests in any Global Note) other than to require delivery of such certificates and other documentation or evidence as are expressly required by, and to do so only if and when expressly required by the terms of, this Supplemental Indenture, and to examine the same to determine

9

substantial compliance as to form with the express requirements hereof. Notwithstanding anything herein to the contrary, neither the Trustee nor the Registrar shall have any responsibility to receive any letters, opinions or certifications, nor any responsibility to monitor compliance with any transfer restrictions, in connection with any transfer or exchange of any beneficial interest in a Global Note for a beneficial interest in the same Global Note.

(g) Notwithstanding the foregoing, in the event that any Transfer Restricted Notes are exchanged for Exchange Notes in connection with an effective registration statement pursuant to the Registration Rights Agreement, the Partnership shall issue and, at the direction of the Partnership, the Trustee shall authenticate the Exchange Notes in exchange for Transfer Restricted Notes accepted for exchange in the exchange offer, which Exchange Notes shall not bear the Restricted Notes Legend, and the Registrar shall rescind any restriction on the transfer of such Exchange Notes.

Section 7. Form of Notes/Legends.

(a) The Notes are being offered only to (A) Persons reasonably believed to be QIBs in reliance on Rule 144A and (B) non-U.S. persons in reliance on Regulation S. Such Notes may thereafter be transferred to, among others, QIBs, and purchasers in reliance on Regulation S, in each case, in accordance with the procedures described herein. Exchange Notes exchanged for interests in the Rule 144A Notes and the Regulation S Notes will be issued in the form of permanent global notes deposited with the Trustee as hereinafter provided, including the appropriate legend set forth in the form of security attached as Exhibit A (the “Exchange Global Notes”). The Exchange Global Notes will be deposited upon issuance with, or on behalf of, the Trustee as custodian for the Depositary, duly executed by the Partnership and authenticated by the Trustee as hereinafter provided. The Exchange Global Notes may be represented by more than one certificate, if so required by the Depositary’s rules regarding the maximum principal amount to be represented by a single certificate.

(b) The Notes offered to QIBs in the United States of America in reliance on Rule 144A (the “Rule 144A Notes”) shall be issued in the form of a permanent global note including appropriate legends as set forth in the form of security attached as Exhibit A (the “Rule 144A Global Notes”), deposited with the Trustee, as custodian for the Depositary, duly executed by the Partnership and authenticated by the Trustee as hereinafter provided. The Rule 144A Global Notes may be represented by more than one certificate, if so required by the Depositary’s rules regarding the maximum principal amount to be represented by a single certificate. The aggregate principal amount of the Rule 144A Global Notes may from time to time be increased or decreased by adjustments made on the records of the Trustee, as custodian for the Depositary, or its nominee, as hereinafter provided.

(c) The Notes offered to non-U.S. persons outside the United States of America (the “Regulation S Notes”) in reliance on Regulation S shall be issued in the form of a permanent global note including appropriate legends as set forth in the form of security attached as Exhibit A (the “Regulation S Global Notes” and, together with the Rule 144A Global Notes and the Exchange Global Notes, the “Global Notes”). Each Regulation S Global Note will be deposited upon issuance with, or on behalf of, the Trustee as custodian for the Depositary. Prior

10

to the 40th day after the date the Notes are issued (such period through and including such 40th day, the “Restricted Period”), interests in the Regulation S Global Notes may only be transferred to non-U.S. persons pursuant to Regulation S, unless exchanged for interests in a Global Note in accordance with the transfer and certification requirements described herein. Investors may hold their interests in the Regulation S Global Note through organizations other than Euroclear or Clearstream that are participants in the Depositary’s system or directly through Euroclear or Clearstream, if they are participants in such systems, or indirectly through organizations which are participants in such systems. If such interests are held through Euroclear or Clearstream, Euroclear and Clearstream will hold such interests in the applicable Regulation S Global Note on behalf of their participants through customers’ securities accounts in their respective names on the books of their respective depositaries. Such depositaries, in turn, will hold such interests in the applicable Regulation S Global Note in customers’ securities accounts in the depositaries’ names on the books of the Depositary. The Regulation S Global Notes may be represented by more than one certificate, if so required by the Depositary’s rules regarding the maximum principal amount to be represented by a single certificate. The aggregate principal amount of the Regulation S Global Notes may from time to time be increased or decreased by adjustments made on the records of the Trustee, as custodian for the Depositary or its nominee, as hereinafter provided.

(d) Unless and until (i) a Note issued as a Transfer Restricted Note is sold under an effective registration statement, (ii) a Note issued as a Transfer Restricted Note is exchanged for an Exchange Note in connection with an effective registration statement pursuant to the Registration Rights Agreement or (iii) the Partnership receives an opinion of counsel satisfactory to it to the effect that neither such legend nor the related restrictions on transfer are required in order to maintain compliance with the provisions of the Securities Act:

(1) each Transfer Restricted Note shall bear the following legend on the face thereof (the “Restricted Notes Legend”):

THIS NOTE HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”), AND MAY NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED EXCEPT IN ACCORDANCE WITH THE FOLLOWING SENTENCE. BY ITS ACQUISITION HEREOF OR OF A BENEFICIAL INTEREST HEREIN, THE ACQUIRER (1) REPRESENTS THAT (A) IT AND ANY ACCOUNT FOR WHICH IT IS ACTING IS A “QUALIFIED INSTITUTIONAL BUYER” (WITHIN THE MEANING OF RULE 144A UNDER THE SECURITIES ACT) AND THAT IT EXERCISES SOLE INVESTMENT DISCRETION WITH RESPECT TO EACH SUCH ACCOUNT, OR (B) IT IS NOT A “U.S. PERSON” (WITHIN THE MEANING OF REGULATION S UNDER THE SECURITIES ACT) AND (2) AGREES FOR THE BENEFIT OF MPLX LP THAT IT WILL NOT OFFER, SELL, PLEDGE OR OTHERWISE TRANSFER THIS NOTE OR ANY BENEFICIAL INTEREST HEREIN, EXCEPT IN ACCORDANCE WITH THE SECURITIES ACT AND ANY APPLICABLE SECURITIES LAWS OF ANY STATE OF THE UNITED STATES AND ONLY (A) TO MPLX LP, (B) PURSUANT TO A REGISTRATION STATEMENT WHICH HAS BECOME EFFECTIVE UNDER THE SECURITIES ACT, (C) TO A QUALIFIED INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A UNDER THE SECURITIES ACT, (D) IN AN OFFSHORE TRANSACTION IN COMPLIANCE WITH RULE 904 OF REGULATION S UNDER THE SECURITIES ACT, OR (E) PURSUANT TO AN EXEMPTION FROM REGISTRATION PROVIDED BY RULE 144 UNDER THE SECURITIES ACT OR ANY OTHER AVAILABLE EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.

11

PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (2)(C) ABOVE OR (2)(D) ABOVE, A DULY COMPLETED AND SIGNED CERTIFICATE (THE FORM OF WHICH MAY BE OBTAINED FROM THE TRUSTEE) MUST BE DELIVERED TO THE TRUSTEE. PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (E) ABOVE, MPLX LP RESERVES THE RIGHT TO REQUIRE THE DELIVERY OF SUCH LEGAL OPINIONS, CERTIFICATIONS OR OTHER EVIDENCE AS MAY REASONABLY BE REQUIRED IN ORDER TO DETERMINE THAT THE PROPOSED TRANSFER IS BEING MADE IN COMPLIANCE WITH THE SECURITIES ACT AND APPLICABLE STATE SECURITIES LAWS. NO REPRESENTATION IS MADE AS TO THE AVAILABILITY OF ANY RULE 144 EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.

(2) each Global Note shall bear the following legend on the face thereof:

UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (“DTC”), NEW YORK, NEW YORK, TO THE PARTNERSHIP OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO., OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

TRANSFERS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS IN WHOLE, BUT NOT IN PART, TO NOMINEES OF DTC OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR’S NOMINEE AND TRANSFERS OF PORTIONS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN THE INDENTURE REFERRED TO HEREIN.

Section 8. Effect of Supplemental Indenture. The provisions of this Supplemental Indenture are intended to supplement those of the Indenture as in effect immediately prior to the execution and delivery hereof. The Indenture shall remain in full force and effect except to the extent that the provisions of the Indenture are expressly modified by the terms of this Supplemental Indenture.

12

Section 9. Governing Law. This Supplemental Indenture and the Notes shall be governed by and construed in accordance with the law of the State of New York, without giving effect to any principles of conflicts of laws thereunder to the extent the application of the laws of another jurisdiction would be required thereby.

Section 10. Trustee Not Responsible for Recitals or Issuance of Notes. The recitals and statements contained herein shall be taken as statements of the Partnership, and the Trustee assumes no responsibility for their correctness. The Trustee makes no representations as to the validity or sufficiency of this Supplemental Indenture or of the Notes other than with respect to the Trustee’s execution of this Supplemental Indenture and authentication of the Notes. The Trustee shall not be accountable for the use or application by the Partnership of the Notes or the proceeds thereof.

Section 11. Conflict with the TIA. If any provision hereof limits, qualifies or conflicts with a provision of the TIA that is required under the TIA to be a part of and govern this Supplemental Indenture, the latter provision shall control. If any provision of this Supplemental Indenture modifies or excludes any provision of the TIA that may be so modified or excluded, the latter provision shall be deemed to apply to this Supplemental Indenture as so modified or to be excluded, as the case may be.

Section 12. Counterparts. This Supplemental Indenture may be executed in any number of counterparts, each of which shall be an original; but such counterparts shall together constitute one and the same instrument. The exchange of copies of this Supplemental Indenture and of signature pages by facsimile or electronic (i.e., “pdf” or “tif”) transmission shall constitute effective execution and delivery of this Supplemental Indenture for all purposes. Signatures of the parties hereto transmitted by facsimile or electronic (i.e., “pdf” or “tif”) transmission shall be deemed to be their original signatures for all purposes of the Supplemental Indenture as to the parties hereto and may be used in lieu of the original.

[The remainder of this page is left blank intentionally]

13

IN WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture to be duly executed as of the day and year first above written.

[Signature Page to Twenty-Second Supplemental Indenture]

[Signature Page to Twenty-Second Supplemental Indenture]

Exhibit A

MPLX LP

5.200% Senior Notes due 2047

[FOR GLOBAL NOTES: UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (“DTC”), NEW YORK, NEW YORK, TO THE PARTNERSHIP OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO., OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

TRANSFERS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS IN WHOLE, BUT NOT IN PART, TO NOMINEES OF DTC OR TO A SUCCESSOR THEREOF OR SUCH SUCCESSOR’S NOMINEE AND TRANSFERS OF PORTIONS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE RESTRICTIONS SET FORTH IN THE INDENTURE REFERRED TO HEREIN.]

[FOR TRANSFER RESTRICTED NOTES: THIS NOTE HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”), AND MAY NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED EXCEPT IN ACCORDANCE WITH THE FOLLOWING SENTENCE. BY ITS ACQUISITION HEREOF OR OF A BENEFICIAL INTEREST HEREIN, THE ACQUIRER (1) REPRESENTS THAT (A) IT AND ANY ACCOUNT FOR WHICH IT IS ACTING IS A “QUALIFIED INSTITUTIONAL BUYER” (WITHIN THE MEANING OF RULE 144A UNDER THE SECURITIES ACT) AND THAT IT EXERCISES SOLE INVESTMENT DISCRETION WITH RESPECT TO EACH SUCH ACCOUNT, OR (B) IT IS NOT A “U.S. PERSON” (WITHIN THE MEANING OF REGULATION S UNDER THE SECURITIES ACT) AND (2) AGREES FOR THE BENEFIT OF MPLX LP THAT IT WILL NOT OFFER, SELL, PLEDGE OR OTHERWISE TRANSFER THIS NOTE OR ANY BENEFICIAL INTEREST HEREIN, EXCEPT IN ACCORDANCE WITH THE SECURITIES ACT

AND ANY APPLICABLE SECURITIES LAWS OF ANY STATE OF THE UNITED STATES AND ONLY (A) TO MPLX LP, (B) PURSUANT TO A REGISTRATION STATEMENT WHICH HAS BECOME EFFECTIVE UNDER THE SECURITIES ACT, (C) TO A QUALIFIED INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A UNDER THE SECURITIES ACT, (D) IN AN OFFSHORE TRANSACTION IN COMPLIANCE WITH RULE 904 OF REGULATION S UNDER THE SECURITIES ACT, OR (E) PURSUANT TO AN EXEMPTION FROM REGISTRATION PROVIDED BY RULE 144 UNDER THE SECURITIES ACT OR ANY OTHER AVAILABLE EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.

PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (2)(C) ABOVE OR (2)(D) ABOVE, A DULY COMPLETED AND SIGNED CERTIFICATE (THE FORM OF WHICH MAY BE OBTAINED FROM THE TRUSTEE) MUST BE DELIVERED TO THE TRUSTEE. PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (E) ABOVE, MPLX LP RESERVES THE RIGHT TO REQUIRE THE DELIVERY OF SUCH LEGAL OPINIONS, CERTIFICATIONS OR OTHER EVIDENCE AS MAY REASONABLY BE REQUIRED IN ORDER TO DETERMINE THAT THE PROPOSED TRANSFER IS BEING MADE IN COMPLIANCE WITH THE SECURITIES ACT AND APPLICABLE STATE SECURITIES LAWS. NO REPRESENTATION IS MADE AS TO THE AVAILABILITY OF ANY RULE 144 EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.]

MPLX LP, a limited partnership duly formed and existing under the laws of the State of Delaware (herein called the “Partnership,” which term includes any successor Person under the Indenture hereinafter referred to), for value received, hereby promises to pay to [•] [Insert if Global Security: CEDE & CO.], or registered assigns, the principal sum of [•] Dollars ($[•]) [Insert if Global Security: , or such greater or lesser amount as indicated on the Schedule of Increases or Decreases in the Principal Amount of Securities attached hereto,] on December 1, 2047, and to pay interest thereon from June 1, 2019 or from the most recent Interest Payment Date to which interest has been paid or duly provided for, semi-annually on June 1 and December 1 in each year commencing December 1, 2019, at the rate of 5.200% per annum, until the principal hereof is paid or made available for payment. Interest on the Notes will be paid on the basis of a 360-day year consisting of twelve 30-day months. The Partnership shall pay Additional Interest, if any, on the applicable Interest Payment Date in the same manner as interest is paid on the Notes and in the amounts set forth in the Registration Rights Agreement. The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date will, as provided in such Indenture, be paid to the Person in whose name this Debt Security (or one or more Predecessor Securities) is registered at the close of business on the Regular Record Date for such interest, which shall be May 15 or November 15 (whether or not a Business Day), as the case may be, next preceding such Interest Payment Date. Any such interest not so punctually paid or duly provided for will forthwith cease to be payable to the Holder on such Regular Record Date and may either be paid to the Person in whose

name this Debt Security (or one or more Predecessor Securities) is registered at the close of business on a Special Record Date for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Debt Securities of this series not less than 10 days prior to such Special Record Date, or be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange on which the Debt Securities of this series may be listed, and upon such notice as may be required by such exchange all as more fully provided in said Indenture. If an Interest Payment Date, a Stated Maturity or a Redemption Date with respect to this Debt Security falls on a day that is not a Business Day, the payment will be made on the next Business Day and no interest will accrue for the period from and after such Interest Payment Date, Stated Maturity or Redemption Date.

Payment of the principal of (and premium, if any) and interest on this Debt Security will be made at the office or agency of the Partnership maintained for that purpose in New York, New York, in such coin or currency of the United States of America as at the time of payment is legal tender for payment of public and private debts; provided, however, that (1) payments on any Global Security shall be made by electronic (same-day) funds transfer to the Depositary and (2) at the option of the Partnership payment of interest may be made by check mailed to the address of the Person entitled thereto as such address shall appear in the Debt Security Register or by electronic funds transfer to an account maintained by the Person entitled thereto as specified in the Debt Security Register, provided that such Person shall have given the Trustee written instructions.

Reference is hereby made to the further provisions of this Debt Security set forth on the reverse hereof, which further provisions shall for all purposes have the same effect as if set forth at this place.

Unless the certificate of authentication hereon has been executed by the Trustee referred to on the reverse hereof by manual signature, this Debt Security shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose.

IN WITNESS WHEREOF, the Partnership has caused this instrument to be duly executed.

Dated:

CERTIFICATE OF AUTHENTICATION

This is one of the Debt Securities of the series designated therein referred to in the within-mentioned Indenture.

Dated:

MPLX LP

5.200% Senior Notes due 2047

This Security is one of a duly authorized issue of Debt Securities of the Partnership (herein called the “Securities”), issued and to be issued in one or more series under a Senior Indenture, dated as of February 12, 2015, as amended or supplemented to date, including as amended and supplemented by the Twenty-Second Supplemental Indenture, dated as of September 23, 2019 (herein called the “Indenture,” which term shall have the meaning assigned to it in such instrument), between the Partnership and The Bank of New York Mellon Trust Company, N.A., as Trustee (herein called the “Trustee,” which term includes any successor trustee under the Indenture), and reference is hereby made to the Indenture for a statement of the respective rights, limitations of rights, duties and immunities thereunder of the Partnership, the Trustee and the Holders of the Securities and of the terms upon which the Securities are, and are to be, authenticated and delivered. This Security is one of the series designated on the face hereof initially limited in aggregate principal amount to $[•].

Prior to June 1, 2047, the Securities are subject to redemption, in whole at any time or in part from time to time, at the election of the Partnership, at a redemption price equal to the greater of (1) 100% of the principal amount of such Securities to be redeemed or (2) the sum of the present values of the remaining scheduled payments of principal and interest on the Securities to be redeemed that would be due if such Securities matured on June 1, 2047 (exclusive of interest accrued to the Redemption Date) discounted to the Redemption Date on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the then current Treasury Rate plus 40 basis points, plus, in either case, accrued and unpaid interest on the principal amount being redeemed to, but not including, the Redemption Date.

On or after June 1, 2047, the Securities are subject to redemption, in whole at any time or in part from time to time, at the election of the Partnership, at a redemption price equal to 100% of the principal amount of such Securities to be redeemed plus accrued and unpaid interest on the principal amount being redeemed to, but not including, the Redemption Date.

For purposes of the redemption provisions of the Securities, the following terms are applicable:

“Business Day” means any Monday, Tuesday, Wednesday, Thursday or Friday that is not a day on which banking institutions in New York, New York are authorized or obligated by law or executive order to close. If a payment date is not a Business Day at a Place of Payment, payment may be made at that place on the next succeeding day that is a Business Day, and no interest shall accrue for the intervening period.

“Comparable Treasury Issue” means the United States Treasury security selected, in accordance with customary financial practice, by an Independent Investment Banker as having a maturity comparable to the remaining term of the Securities (assuming for this purpose that the Securities matured on June 1, 2047) (the “Remaining Life”) to be redeemed that would be utilized, at the time of selection and in accordance with customary financial practice, in pricing new issues of corporate debt securities of comparable maturity to the remaining term of such Securities (assuming that the Securities matured on June 1, 2047).

“Comparable Treasury Price” means, with respect to any Redemption Date, (1) the average, as determined by the Partnership, of the Reference Treasury Dealer Quotations for such Redemption Date, after excluding the highest and lowest Reference Treasury Dealer Quotations, or (2) if the Partnership obtains fewer than four such Reference Treasury Dealer Quotations, the average of all such quotations.

“Independent Investment Banker” means one of the Reference Treasury Dealers that the Partnership appoints to act as the Independent Investment Banker from time to time.

“Reference Treasury Dealer” means at least four primary U.S. Government securities dealers in The City of New York as the Partnership shall select.

“Reference Treasury Dealer Quotations” means, with respect to each Reference Treasury Dealer and any Redemption Date, the average, as determined by the Partnership, of the bid and asked prices for the Comparable Treasury Issue (expressed in each case as a percentage of its principal amount) quoted in writing to the Partnership by such Reference Treasury Dealer at 3:30 p.m., New York City time, on the third Business Day preceding such Redemption Date.

“Treasury Rate” means, as of any Redemption Date, the rate per year equal to: (1) the yield, under the heading which represents the average for the immediately preceding week, appearing in, or available through, the most recently published statistical release designated “H.15” or any successor publication which is published weekly by the Board of Governors of the Federal Reserve System (or companion online data resource published by the Board of Governors of the Federal Reserve System) and which established yields on actively traded United States Treasury securities adjusted to constant maturity under the caption “Treasury Constant Maturities,” for the maturity corresponding to the applicable Comparable Treasury Issue; provided that, if no maturity is within three months before or after the Remaining Life of the Notes to be redeemed, yields for the two published maturities most closely corresponding to the applicable Comparable Treasury Issue will be determined and the Treasury Rate will be interpolated or extrapolated from such yields on a straight line basis, rounding to the nearest month; or (2) if such release (or any successor release) is not published during the week preceding the calculation date or does not contain such yields, the rate per year equal to the semi-annual equivalent yield to maturity of the applicable Comparable Treasury Issue, calculated using a price for the applicable Comparable Treasury Issue (expressed as a percentage of its principal amount) equal to the related Comparable Treasury Price for such Redemption Date. The Treasury Rate will be calculated by the Partnership on the third Business Day preceding the Redemption Date.

Notice of the redemption will be transmitted to holders of Securities at least 10 and not more than 60 days prior to the Redemption Date. If fewer than all of the Securities are to be redeemed, the Trustee will select the particular Securities or portions thereof for redemption from the outstanding Securities not previously called by any of the following methods: (i) in compliance with the requirements of the principal national securities exchange, if any, on which such Securities are listed, (2) on a pro rata basis to the extent practicable and in accordance with the procedures of the Depositary or (3) by lot or in such other similar method in accordance with the procedures of the depositary of such Securities.

Unless the Partnership defaults in payment of the redemption price, on or after the Redemption Date, interest will cease to accrue on the Securities or portions thereof called for redemption.

In the event of redemption of this Security in part only, a new Security or Securities of this series and of like tenor for the unredeemed portion hereof will be issued in the name of the Holder hereof upon the cancellation hereof.

The Indenture contains provisions for defeasance at any time of the entire indebtedness of this Security or of certain restrictive covenants and Events of Default with respect to this Security, in each case upon compliance with certain conditions set forth in the Indenture.

The Indenture contains provisions permitting the Partnership and the Trustee to modify the Indenture or any supplemental indenture without the consent of the Holders for one or more of the following purposes: (1) to evidence the succession of another Person to the Partnership; (2) to surrender any right or power conferred by the Indenture, to add to the covenants for the protection of the Holders of the Securities or to add additional defaults or events of default; (3) to cure any ambiguity, to correct or supplement any provision of the Indenture which may be defective or inconsistent with any other provision of the Indenture, or to make any other provisions with respect to matters or questions arising under the Indenture as shall not adversely affect the interests of the Holders; (4) to permit qualification of the Indenture or any supplemental indenture under the TIA; (5) to permit or facilitate the issuance of Debt Securities of any series in uncertificated form; (6) to secure any or all Debt Securities; (7) to make any change that does not adversely affect the rights of any Holder; (8) to add to, change or eliminate any of the provisions of the Indenture in respect of one or more Debt Securities, under certain conditions specified therein; (9) to evidence and provide acceptance of appointment thereunder by a successor or separate Trustee and to add to or change the provisions under the Indenture as necessary; and (10) to establish the form or terms of Debt Securities of a particular series as permitted by Sections 2.01 and 2.03 of the Indenture.

The Indenture also permits, with certain exceptions as therein provided, the amendment thereof and the modification of the rights and obligations of the Partnership and the rights of the Holders of the Securities of each series to be affected under the Indenture at any time by the Partnership and the Trustee with the consent of the Holders of not less than a majority in aggregate principal amount of the Securities at the time

Outstanding of each series to be affected. The Indenture also contains provisions permitting the Holders of at least a majority in aggregate principal amount of the Securities at the time Outstanding, on behalf of the Holders of all Securities, to waive compliance by the Partnership with certain provisions of the Indenture and certain past defaults under the Indenture and their consequences. Any such consent or waiver by the Holder of this Security shall be conclusive and binding upon such Holder and upon all future Holders of this Security and of any Security issued upon the registration of transfer hereof or in exchange herefor or in lieu hereof, whether or not notation of such consent or waiver is made upon this Security.

As provided in and subject to the provisions of the Indenture, the Holder of this Security shall not have the right to institute any proceeding with respect to the Indenture or for the appointment of a receiver or trustee or for any other remedy thereunder, unless such Holder shall have previously given the Trustee written notice of a continuing Event of Default with respect to the Securities, the Holders of not less than 25% in aggregate principal amount of the Securities then Outstanding shall have made written request to the Trustee to institute proceedings in respect of such Event of Default as Trustee and offered the Trustee indemnity, and the Trustee shall not have received from the Holders of a majority in principal amount of the Securities then Outstanding a direction inconsistent with such request, and shall have failed to institute any such proceeding, for 60 days after receipt of such notice, request and offer of indemnity. The foregoing shall not apply to any suit instituted by the Holder of this Security for the enforcement of any payment of principal hereof or any premium or interest hereon on or after the respective due dates expressed herein.

No reference herein to the Indenture and no provision of this Security or of the Indenture shall alter or impair the obligation of the Partnership, which is absolute and unconditional, to pay the principal of and any premium and interest on this Security at the times, place and rate, and in the coin or currency, herein prescribed.

As provided in the Indenture and subject to certain limitations therein set forth, the transfer of this Security is registrable in the Debt Security Register, upon surrender of this Security for registration of transfer at the office or agency of the Partnership in any place where the principal of and any premium and interest on this Security are payable, duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Partnership and the Registrar duly executed by, the Holder hereof or his attorney duly authorized in writing, and thereupon one or more new Securities and of like tenor, of authorized denominations and for the same aggregate principal amount, will be issued to the designated transferee or transferees.

The Securities are issuable only in registered form without coupons in denominations of $2,000 and integral multiples of $1,000 in excess thereof. As provided in the Indenture and subject to certain limitations therein set forth, the Securities are exchangeable for a like aggregate principal amount of Securities and of like tenor of a different authorized denomination, as requested by the Holder surrendering the same.

No service charge shall be made for any such registration of transfer or exchange, but, subject to any applicable provisions of the Indenture, the Partnership may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection therewith.

Prior to due presentment of this Security for registration of transfer, the Partnership, the Trustee and any agent of the Partnership or the Trustee may treat the Person in whose name this Security is registered as the owner hereof for all purposes, whether or not this Security be overdue, and neither the Partnership, the Trustee nor any such agent shall be affected by notice to the contrary.

All terms used in this Security which are defined in the Indenture shall have the meaning assigned to them in the Indenture.

FORM OF ASSIGNMENT

ABBREVIATIONS

Customary abbreviations may be used in the name of a Securityholder or an assignee, such as TEN COM (=tenants in common), TEN ENT (=tenants by the entireties), JT TEN (=joint tenants with rights of survivorship and not as tenants in common), CUST (=custodian), and U/G/M/A (=Uniform Gift to Minors Act).

Additional abbreviations may also be used though not in the above list.

FOR VALUE RECEIVED, the undersigned hereby sell(s),

assign(s) and transfer(s) unto

Please insert Social Security or

other identifying number of assignee

PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING POSTAL ZIP CODE, OF ASSIGNEE

the within Security and all rights thereunder, hereby irrevocably constituting and appointing                              attorney to transfer said Security on the books of the Partnership, with full power of substitution in the premises.

EXHIBIT B

FORM OF CERTIFICATE TO BE DELIVERED UPON EXCHANGE OR REGISTRATION OF TRANSFER OF NOTES

Re: 5.200% Senior Notes due 2047 (the “Notes”) of MPLX LP (the “Partnership”)

This Certificate relates to $                     principal amount of Notes held in book-entry or definitive form by (the “Transferor”). The Transferor has requested the Registrar by written order to exchange or register the transfer of a Note or Notes or beneficial interests therein (the “Transfer”).

In connection with such request and in respect of each such Note or beneficial interest therein, the Transferor does hereby certify that the Transferor is familiar with the Indenture relating to the above-captioned Notes and that the Transfer does not require registration under the Securities Act of 1933, as amended (the “Securities Act”), because:

Fill in blank or check appropriate item, as applicable.

EXHIBIT C

FORM OF CERTIFICATE TO BE DELIVERED IN CONNECTION WITH TRANSFERS

PURSUANT TO REGULATION S

Re: 5.200% Senior Notes due 2047 (the “Notes”) of MPLX LP (the “Partnership”)

This Certificate relates to $                      principal amount of Notes held in book-entry form by (the “Transferor”).

The Transferor has requested the Registrar by written order to exchange or register the transfer of a Note or Notes or beneficial interests therein (the “Transfer”) for an interest in the Regulation S Temporary Global Note to be held with [Euroclear] [Clearstream] through the Depositary (in each case as defined in the Indenture related to the above-referenced Notes).

In connection with such request and in respect of each such Note or beneficial interest therein, the Transferor does hereby certify that the Transferor is familiar with such Indenture and Establishment Action and that:

(a) the offer of such Notes or beneficial interests was not made to a person in the United States or for the benefit of a person in the United States (other than an Initial Purchaser);

(b) at the time the buy order was originated, the transferee was outside the United States or the Transferor and any person acting on its behalf reasonably believed that the transferee was outside the United States; or the transaction was executed in, on or through the facilities of a designated offshore securities market and neither the Transferor nor any person acting on its behalf knows that the transaction was prearranged with a buyer in the United States;

(c) no directed selling efforts have been made by the Transferor in the United States in contravention of the requirements of Rule 903(a) or Rule 904(a) of Regulation S under the U.S. Securities Act of 1933, as amended (the “Securities Act”), as applicable;

(d) the transaction is not part of a plan or scheme to evade the registration requirements of the Securities Act; and

(e) if the proposed transfer is being made prior to the expiration of a 40-day “distribution compliance period” as defined in Regulation S under the Securities Act, the transfer is being made (a) to a person that is not a U.S. person or for the account or benefit of a person that is not a U.S. person within the meaning of Regulation S under the Securities Act; or (b) to a “qualified institutional buyer” within the meaning of Rule 144A under the Securities Act, in each case that holds such Note or beneficial interests through [Euroclear] [Clearstream].

EXHIBIT 4.7

REGISTRATION RIGHTS AGREEMENT

by and among

MPLX LP, as Issuer,

and

MPLX GP LLC, as General Partner,

and

Barclays Capital Inc.,

MUFG Securities Americas Inc.

and

Wells Fargo Securities, LLC, as Dealer Managers

Dated as of September 23, 2019

REGISTRATION RIGHTS AGREEMENT

This Registration Rights Agreement (this “Agreement”) is made and entered into this 23rd day of September, 2019, by and among MPLX LP, a Delaware limited partnership (the “Partnership”), MPLX GP LLC, a Delaware limited liability company and the general partner of the Partnership (the “General Partner”), and Barclays Capital Inc., MUFG Securities Americas Inc. and Wells Fargo Securities, LLC (collectively, the “Dealer Managers”).

This Agreement is made pursuant to the Offering Memorandum and Consent Solicitation Statement dated August 22, 2019 (as amended or supplemented, the “Offering Memorandum”), which provides for the offers by the Partnership to exchange any and all of the outstanding 6.250% Senior Notes due 2022, 3.500% Senior Notes due 2022, 6.375% Senior Notes due 2024, 5.250% Senior Notes due 2025, 4.250% Senior Notes due 2027 and 5.200% Senior Notes due 2047 (collectively, the “Old ANDX Notes”) issued by Andeavor Logistics LP (f/k/a Tesoro Logistics LP), a Delaware limited partnership (“ANDX”) and a wholly owned subsidiary of MPLX, and Tesoro Logistics Finance Corp., a Delaware corporation (together with ANDX, the “Issuers”) and a subsidiary of ANDX, in exchange for newly issued debt securities of the Partnership (the “New MPLX Notes”), in each case maturing on the same date and bearing an interest rate of the same amount per annum as the applicable series of Old ANDX Notes for which they are exchanged and cash, on the terms and subject to the conditions set forth in the Offering Memorandum. The execution of this Agreement is a condition to the consummation of the Original Exchange Offer (as defined below).

In consideration of the foregoing, the parties hereto agree as follows:

1. Definitions. As used in this Agreement, the following capitalized defined terms shall have the following meanings:

“Additional Interest” shall have the meaning set forth in Section 2.5.

“Affiliate” shall mean an “affiliate” as that term is defined in Rule 405 under the Securities Act.

“Agreement” shall have the meaning set forth in the preamble.

“ANDX” shall have the meaning set forth in the preamble.

“Automatic Shelf Registration Statement” shall mean an “automatic shelf registration statement” as that term is defined in Rule 405 under the Securities Act.

“Dealer Managers” shall have the meaning set forth in the preamble.

“Dealer Manager Agreement” means the Dealer Manager Agreement, dated August 22, 2019, by and among the Partnership, the General Partner and the Dealer Managers.

“Depositary” shall mean The Depository Trust Company, or any other depositary appointed by the Partnership; provided, however, that such depositary must have an address in the Borough of Manhattan, in the City of New York.

“Event Date” shall have the meaning set forth in Section 2.5.

“Exchange Date” shall have the meaning set forth in the Dealer Manager Agreement.

“Exchange Offer” means the offer by the Partnership to exchange each Series of Registrable Securities for the corresponding Series of Exchange Securities pursuant to Section 2.1.

“Exchange Offer Registration Statement” shall mean an exchange offer registration statement on Form S-4 (or, if applicable, on another appropriate form), and all amendments and supplements to such registration statement, including the Prospectus contained therein, all exhibits thereto and all material incorporated or deemed incorporated by reference therein.

“Exchange Period” shall have the meaning set forth in Section 2.1.

“Exchange Securities” shall mean with respect to each series of New MPLX Notes, a new series of notes maturing on the same date and bearing interest at the same rate per annum as the corresponding series of New MPLX Notes (each such series of Exchange Securities, a “Series of Exchange Securities”), in each case issued by the Partnership under the Indenture, containing terms identical to the applicable Series of New MPLX Notes in all material respects (except for references to certain additional interest rate provisions, restrictions on transfers and restrictive legends), to be offered to Holders of the applicable Series of New MPLX Notes in exchange for the corresponding Series of Registrable Securities pursuant to the Exchange Offer.

“General Partner” shall have the meaning set forth in the preamble.

“Holder” shall mean each Person who becomes the registered owner of Registrable Securities under the Indenture and each Participating Broker-Dealer that holds Exchange Securities for so long as such Participating Broker-Dealer is required to deliver a Prospectus in connection with any resale of such Exchange Securities.

“Indenture” shall mean the Senior Indenture, dated as of February 12, 2015 between the Partnership and The Bank of New York Mellon Trust Company, N.A., as the trustee, as the same may be amended, supplemented, waived or otherwise modified from time to time in accordance with the terms thereof.

“Majority Holders” shall mean the Holders of a majority of the aggregate principal amount of Outstanding (as defined in the Indenture) Registrable Securities; provided, that whenever the consent or approval of Holders of a specified percentage of Registrable Securities is required hereunder, Registrable Securities held by the Partnership or any Affiliate of the Partnership shall be disregarded in determining whether such consent or approval was given by the Holders of such required percentage amount.

“New MPLX Notes” shall have the meaning set forth in the preamble.

“Offering Memorandum” shall have the meaning set forth in the preamble.

“Old ANDX Notes” shall have the meaning set forth in the preamble.

2

“Original Exchange Offer” means the offer by the Partnership to exchange any and all outstanding Old ANDX Notes for New MPLX Notes, on the terms and conditions set forth in the Offering Memorandum.

“Participating Broker-Dealers” shall mean the Dealer Managers and any other broker-dealer which makes a market in the New MPLX Notes and exchanges Registrable Securities in the Exchange Offer for Exchange Securities.

“Partnership” shall have the meaning set forth in the preamble and shall also include the Partnership’s successors.

“Person” shall mean an individual, partnership (general or limited), corporation, limited liability company, trust or unincorporated organization, or a government or agency or political subdivision thereof.

“Prospectus” shall mean the prospectus included in a Registration Statement, including any preliminary prospectus, and any such prospectus as amended or supplemented by any prospectus supplement, including any such prospectus supplement with respect to the terms of the offering of any portion of the Registrable Securities covered by a Shelf Registration Statement, and by all other amendments and supplements to a prospectus, including post-effective amendments, and in each case including all material incorporated or deemed incorporated by reference therein.

“Registrable Securities” shall mean the New MPLX Notes; provided, however, that the New MPLX Notes shall cease to be Registrable Securities when (i) a Registration Statement with respect to such New MPLX Notes shall have been declared or otherwise become effective under the Securities Act and such New MPLX Notes shall have been disposed of pursuant to such Registration Statement, (ii) such New MPLX Notes may be resold without restriction pursuant to Rule 144 (or any similar provision then in force, but not Rule 144A) under the Securities Act, (iii) such New MPLX Notes shall have ceased to be outstanding or (iv) the Exchange Offer is consummated (except in the case of New MPLX Notes which may not be exchanged in the Exchange Offer). Each of the series of New MPLX Notes may be referred to herein as a “Series of Registrable Securities.”

“Registration Default” shall have the meaning set forth in Section 2.5.

“Registration Expenses” shall mean any and all expenses incident to performance of or compliance by the Partnership with this Agreement, including without limitation: (i) all SEC or Financial Industry Regulatory Authority (“FINRA”) registration and filing fees, (ii) all fees and expenses incurred in connection with compliance with state securities or blue sky laws, (iii) all expenses of any Persons in preparing or assisting in preparing, word processing, printing and distributing any Registration Statement, any Prospectus, any amendments or supplements thereto, any underwriting agreements, securities sales agreements and other documents relating to the performance of and compliance with this Agreement, (iv) all rating agency fees, (vi) the fees and disbursements of counsel for the Partnership and of the independent public accountants of the Partnership, including the expenses of any special audits or “cold comfort” letters required by or incident to such performance and compliance, (vi) the fees and expenses of the Trustee,

3

and any escrow agent or custodian, (vii) the reasonable fees and expenses of counsel to the Dealer Managers in connection therewith, (viii) any fees and disbursements of the underwriters customarily required to be paid by issuers or sellers of securities and the fees and expenses of any special experts retained by the Partnership in connection with any Registration Statement, but excluding underwriting discounts and commissions and transfer taxes, if any, relating to the sale or disposition of Registrable Securities by a Holder.

“Registration Statement” shall mean any registration statement of the Partnership which covers any of the Exchange Securities or Registrable Securities pursuant to the provisions of this Agreement, and all amendments and supplements to any such Registration Statement, including post-effective amendments, in each case including the Prospectus contained therein, all exhibits thereto and all material incorporated or deemed incorporated by reference therein.

“SEC” shall mean the United States Securities and Exchange Commission or any successor agency or government body performing the functions currently performed by the United States Securities and Exchange Commission.

“Securities Act” shall mean the Securities Act of 1933, as amended.

“Securities Exchange Act” shall mean the Securities Exchange Act of 1934, as amended.

“Series of New MPLX Notes” shall mean each series of New MPLX Notes.

“Shelf Registration” shall mean a registration effected pursuant to Section 2.2.

“Shelf Registration Statement” shall mean a “shelf” registration statement of the Partnership pursuant to the provisions of Section 2.2, including an Automatic Shelf Registration Statement, if applicable, which covers all of the Registrable Securities on an appropriate form under Rule 415 under the Securities Act, or any similar rule that may be adopted by the SEC, and all amendments and supplements to such Registration Statement, including post-effective amendments, in each case including the Prospectus contained therein, all exhibits thereto and all material incorporated or deemed incorporated by reference therein.

“Trustee” shall mean the trustee with respect to the Registrable Securities under the Indenture.

“Trust Indenture Act” shall mean the Trust Indenture Act of 1939.

2. Registration Under the Securities Act.

2.1. Exchange Offer. Unless the Exchange Offer would violate applicable law or any applicable interpretation of the staff of the SEC, the Partnership shall, for the benefit of the Holders, at the Partnership’s cost, use its commercially reasonable efforts to (A) prepare and, not later than 180 calendar days following the Exchange Date, file with the SEC an Exchange Offer Registration Statement on an appropriate form under the Securities Act with respect to a proposed Exchange Offer and the issuance and delivery to the Holders, in exchange for each Series of Registrable Securities, of a like principal amount of the corresponding Series of Exchange Securities, (B) cause the Exchange Offer Registration Statement to be declared

4

effective under the Securities Act within 255 calendar days after the Exchange Date, (C) keep the Exchange Offer Registration Statement effective until the closing of the Exchange Offer and (D) cause the Exchange Offer to be consummated not later than 365 calendar days following the Exchange Date. After the effectiveness of the Exchange Offer Registration Statement, the Partnership shall promptly commence the Exchange Offer, it being the objective of such Exchange Offer to enable each Holder eligible and electing to exchange Registrable Securities for Exchange Securities (assuming that such Holder (a) is not an Affiliate of the Partnership, (b) is not a broker-dealer who tendered Old ANDX Notes acquired directly from the Issuers for its own account in exchange for New MPLX Notes, (c) is acquiring the Exchange Securities in the ordinary course of such Holder’s business and (d) is not engaged in and does not intend to engage in and has no arrangements or understandings with any Person to participate in the distribution of the Exchange Securities) to transfer such Exchange Securities from and after their receipt without any limitations or restrictions under the Securities Act and under state securities or blue sky laws.

In order to participate in the Exchange Offer, each Holder must represent to the Partnership at the time of the consummation of the Exchange Offer (which representation shall be contained in a document accompanying the Exchange Offer Registration Statement) that it (i) is not an Affiliate of the Partnership, (ii) is not a broker-dealer who tendered Old ANDX Notes acquired directly from the Issuers for its own account in exchange for New MPLX Notes, (iii) is acquiring the Exchange Securities in the ordinary course of such Holder’s business and (iv) is not engaged in and does not intend to engage in and has no arrangements or understandings with any Person to participate in the distribution of the Exchange Securities.

In connection with the Exchange Offer, the Partnership shall:

(a) make available to each Holder a copy of the Prospectus forming part of the Exchange Offer Registration Statement;

(b) keep the Exchange Offer open for acceptance for a period of not less than 20 business days after the date notice thereof is mailed to the Holders (or longer at the option of the Partnership or if required by applicable law) (such period referred to herein as the “Exchange Period”);

(c) utilize the services of the Depositary for the Exchange Offer;

(d) permit Holders to withdraw tendered Registrable Securities at any time prior to the expiration of the Exchange Period, by sending to the institution specified in an applicable notice, a telegram, telex, facsimile transmission or letter setting forth the name of such Holder, the principal amount of Registrable Securities delivered for exchange, and a statement that such Holder is withdrawing such Holder’s election to have such Registrable Securities exchanged; and

(e) otherwise comply in all material respects with all applicable laws relating to the Exchange Offer.

The Exchange Securities shall be issued under (i) the Indenture or (ii) an indenture identical in all material respects to the Indenture and which, in either case, has been qualified under the Trust Indenture Act. The Indenture or such indenture shall provide that each series of Exchange Securities and the corresponding series of New MPLX Notes shall vote and consent together on all matters as a single class.

5

As soon as reasonably practicable after the expiration of the Exchange Offer, the Partnership shall:

(i) accept for exchange all Registrable Securities duly tendered and not validly withdrawn pursuant to the Exchange Offer in accordance with the terms of the Exchange Offer Registration Statement;

(ii) deliver to the Trustee for cancellation all Registrable Securities so accepted for exchange; and

(iii) cause the Trustee promptly to authenticate and deliver Exchange Securities to each Holder of Registrable Securities so accepted for exchange in a principal amount equal to the principal amount of the corresponding Series of Registrable Securities of such Holder so accepted for exchange.

Interest on each Exchange Security will accrue from the last date on which interest was paid on the Registrable Security surrendered in exchange therefor or, if no interest has been paid on the Registrable Security, from the date of original issuance. The Exchange Offer shall not be subject to any conditions, other than (i) that the Exchange Offer, or the making of any exchange by a Holder, does not violate applicable law or any applicable interpretation of the staff of the SEC, (ii) the due tendering of Registrable Securities in accordance with the Exchange Offer, (iii) that each Holder of Registrable Securities exchanged in the Exchange Offer shall have represented that it (A) is not an Affiliate of the Partnership, (B) is not a broker-dealer who tendered Old ANDX Notes acquired directly from the Issuers for its own account in exchange for New MPLX Notes, (C) will acquire the Exchange Securities in the ordinary course of such Holder’s business and (D) is not engaged in and does not intend to engage in and has no arrangements or understandings with any Person to participate in the distribution of the Exchange Securities and shall have made such other representations as may be reasonably necessary under applicable SEC rules, regulations or interpretations to render the use of Form S-4 or other appropriate form under the Securities Act available and (iv) that no action or proceeding shall have been instituted or threatened in any court or by or before any governmental agency with respect to the Exchange Offer which, in the Partnership’s judgment, would reasonably be expected to impair the ability of the Partnership to proceed with the Exchange Offer. The Partnership will use its commercially reasonable efforts to cause the registrar for each Series of Registrable Securities to furnish to the Dealer Managers with the names and addresses of the Holders to whom the Exchange Offer is made, and the Dealer Managers shall have the right to contact such Holders and otherwise facilitate the tender of Registrable Securities in the Exchange Offer.

2.2. Shelf Registration. (i) If, because of any changes in law, SEC rules or regulations or applicable interpretations thereof by the staff of the SEC, the Partnership determines upon the advice of its counsel that it is not permitted to effect the Exchange Offer as contemplated by Section 2.1, (ii) if for any other reason the Exchange Offer is not consummated within 365 days after the original Exchange Date or (iii) if a Holder notifies the Partnership in writing prior to the 20th day following the consummation of the Exchange Offer that it is not permitted by applicable law to participate in the Exchange Offer or participates in the Exchange Offer and does not receive fully tradeable Exchange Securities pursuant to the Exchange Offer, then in case of each of clauses (i) through (iii) the Partnership shall, at its reasonable cost:

6

(a) As promptly as practicable, but no later than 90 days after being required to do so under this Section 2.2, file with the SEC, and thereafter shall use its commercially reasonable efforts to cause to become effective as promptly as practicable but no later than 270 days after being required to do so under this Section 2.2, a Shelf Registration Statement relating to the offer and sale of the Registrable Securities by the Holders from time to time in accordance with the methods of distribution elected by the Majority Holders participating in the Shelf Registration and set forth in such Shelf Registration Statement; provided, however, that nothing in this Section 2.2(a) shall require the filing of a Shelf Registration Statement prior to the deadline for filing the Exchange Offer Registration Statement set forth in Section 2.1; provided, further, that no Holder shall be entitled to be named as a selling security holder in the Shelf Registration Statement or to use the Prospectus forming a part thereof for resales of Registrable Securities unless such Holder has signed and returned to the Partnership a notice and questionnaire as distributed by the Partnership consenting to such Holder’s inclusion in the Prospectus as a selling security holder, evidencing such Holder’s agreement to be bound by the applicable provisions of this Agreement and providing such further information to the Partnership as the Partnership may reasonably request.

(b) Use its commercially reasonable efforts to keep the Shelf Registration Statement continuously effective in order to permit the Prospectus forming part thereof to be usable by Holders for a period of one year from the Exchange Date, or for such shorter period that will terminate when all Registrable Securities covered by the Shelf Registration Statement have been sold pursuant to the Shelf Registration Statement or cease to be outstanding or otherwise to be Registrable Securities.

(c) Notwithstanding any other provisions hereof, use its commercially reasonable efforts to ensure that (i) any Shelf Registration Statement and any amendment thereto, at the time each such registration statement or amendment thereto becomes effective, and any Prospectus as of the date thereof forming part thereof and any supplement thereto complies in all material respects with the Securities Act and the rules and regulations thereunder, (ii) any Shelf Registration Statement and any amendment thereto does not, when it becomes effective, contain an untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading and (iii) any Prospectus forming part of any Shelf Registration Statement, and any supplement to such Prospectus (as amended or supplemented from time to time) (each, as of the date thereof), does not include an untrue statement of a material fact or omit to state a material fact necessary in order to make the statements, in the light of the circumstances under which they were made, not misleading.

The Partnership further agrees, if necessary, to supplement or amend the Shelf Registration Statement, as required by Section 3(b), and to furnish to the Holders of Registrable Securities copies of any such supplement or amendment promptly after its being used or filed with the SEC (other than with respect to any such supplement or amendment resulting solely from the incorporation by reference of any report filed under the Securities Exchange Act). In the event that the Exchange Offer is consummated within 365 days after the Exchange Date, the Partnership shall have no obligation to file a Shelf Registration Statement pursuant to Section 2.2(ii).

7

2.3. Expenses. The Partnership shall pay all Registration Expenses in connection with the registration pursuant to Section 2.1 or 2.2. Each Holder shall pay all underwriting discounts and commissions and transfer taxes, if any, relating to the sale or disposition of such Holder’s Registrable Securities pursuant to the Shelf Registration Statement.

2.4. Effectiveness. An Exchange Offer Registration Statement pursuant to Section 2.1 will not be deemed to have become effective unless it has been declared effective by the SEC, and a Shelf Registration Statement pursuant to Section 2.2 will not be deemed to have become effective unless it has been declared effective by the SEC or has otherwise become effective under Rule 462 under the Securities Act or any other applicable rule; provided, however, that if, after such Registration Statement has been declared effective or has otherwise become effective, the offering of Registrable Securities pursuant to an Exchange Offer Registration Statement or a Shelf Registration Statement is interfered with by any stop order, injunction or other order or requirement of the SEC or any other governmental agency or court, such Registration Statement will be deemed not to have become effective during the period of such interference, until the offering of Registrable Securities pursuant to such Registration Statement may legally resume.

2.5. Interest. The Partnership agrees that in the event that (a) (i) if required, the Exchange Offer is not consummated on or prior to the 365th calendar day following the Exchange Date or (ii) if required, a Shelf Registration Statement has not become effective on or prior to the 270th calendar day following the date on which the Partnership became obligated to file such Shelf Registration Statement under Section 2.2, or (b) if required, the Shelf Registration Statement has been filed and is declared or otherwise becomes effective but ceases to be effective or usable for a period of time that exceeds 120 days in the aggregate in any 12-month period in which it is required to be effective hereunder (each such event referred to in the preceding clauses (a) and (b), a “Registration Default”), the interest rate borne by each series of the New MPLX Notes affected thereby shall be increased (“Additional Interest”) immediately upon occurrence of a Registration Default by one-quarter of one percent (0.25%) per annum with respect to the first 90-day period while one or more Registration Defaults is continuing and will increase to a maximum of one-half of one percent (0.50%) per annum Additional Interest thereafter while one or more Registration Defaults is continuing until all Registration Defaults have been cured; provided that Additional Interest shall accrue only for those days that a Registration Default occurs and is continuing, including the date on which any Registration Default shall occur but not including the date on which all Registration Defaults have been cured. Such Additional Interest shall be calculated based on a year consisting of 360 days comprised of twelve 30-day months. Following the cure of all Registration Defaults the accrual of Additional Interest on the affected New MPLX Notes will cease, the interest rate will revert to the original rate on such New MPLX Notes and, upon any subsequent Registration Default following any such cure of all Registration Defaults, Additional Interest will begin accruing again at one-quarter of one percent (0.25%) per annum and will increase to a maximum of one-half of one percent (0.50%) per annum as provided above until all Registration Defaults have been cured. Additional Interest shall not be payable with respect to Registration Defaults for any period during which a Shelf Registration Statement is effective and usable by the Holders. Any

8

Additional Interest shall constitute liquidated damages and shall be the exclusive remedy, monetary or otherwise, available to any Holder of New MPLX Notes with respect to any Registration Default. The Partnership shall notify the Trustee within five business days after each and every date on which an event occurs in respect of which Additional Interest is required to be paid (an “Event Date”). Additional Interest shall be paid by depositing with the Trustee, in trust, for the benefit of the Holders of Registrable Securities, on or before the applicable semi-annual interest payment date, immediately available funds in sums sufficient to pay the Additional Interest then due. The Additional Interest due shall be payable on each interest payment date to the record Holder of New MPLX Notes affected thereby entitled to receive the interest payment to be paid on such date as set forth in the Indenture. Each obligation to pay Additional Interest shall be deemed to accrue from and including the day following the applicable Event Date.

Notwithstanding anything else contained herein, no Additional Interest shall be payable in relation to the applicable Shelf Registration Statement or the related Prospectus if (i) such Additional Interest is payable solely as a result of (x) the filing of a post-effective amendment to such Shelf Registration Statement to incorporate annual audited or, if required by the rules and regulations under the Securities Act, quarterly unaudited financial information with respect to the Partnership where such post-effective amendment is not yet effective and needs to be declared or otherwise become effective to permit Holders to use the related Prospectus or (y) the Partnership notifies the Holder to suspend use (on one or more occasions) of the Shelf Registration Statement and the related Prospectus for a period not to exceed an aggregate of 120 days in any calendar year because of the occurrence of any material event or development with respect to the Partnership that, in the reasonable judgment of the Partnership, would be detrimental to the Partnership if so disclosed or would otherwise materially adversely affect a financing, acquisition, disposition, merger or other material transaction; provided, however, that in no event shall the Partnership be required to disclose the business purpose for such suspension. Notwithstanding the foregoing, the Partnership shall not be required to pay Additional Interest with respect to the New MPLX Notes to any Holder if the failure arises from the Partnership’s failure to file, or cause to become effective, a Shelf Registration Statement within the time periods specified in this Section 2 by reason of the failure of such Holder to provide such information as (i) the Partnership may reasonably request, with reasonable prior written notice, for use in the Shelf Registration Statement or any Prospectus included therein to the extent the Partnership reasonably determines that such information is required to be included therein by applicable law, (ii) FINRA or the SEC may request in connection with such Shelf Registration Statement or (iii) is required to comply with the agreements of such Holder as contained herein to the extent compliance thereof is necessary for the Shelf Registration Statement to be declared or otherwise become effective, including, without limitation, a signed notice and questionnaire as distributed by the Partnership consenting to such Holder’s inclusion in the Prospectus as a selling security holder, evidencing such Holder’s agreement to be bound by the applicable provisions of this Agreement and providing such further information to the Partnership as the Partnership may reasonably request.

9

3. Registration Procedures. In connection with the obligations of the Partnership with respect to Registration Statements pursuant to Sections 2.1 and 2.2, the Partnership shall:

(a) prepare and file with the SEC a Registration Statement, within the relevant time period specified in Section 2, on the appropriate form under the Securities Act, which form (i) shall be selected by the Partnership, (ii) shall, in the case of a Shelf Registration, be available for the sale of the Registrable Securities by the eligible selling Holders thereof, and (iii) shall, at the time of effectiveness, comply as to form in all material respects with the requirements of the applicable form and include or incorporate by reference all financial statements required by the SEC to be filed therewith or incorporated by reference therein, and use its commercially reasonable efforts to cause such Registration Statement to become effective and remain effective in accordance with Section 2;

(b) subject to the Partnership’s right to suspend use of a Shelf Registration Statement contained in the second paragraph of Section 2.5, prepare and file with the SEC such amendments and post-effective amendments to each Registration Statement as may be necessary under applicable law to keep such Registration Statement effective for the applicable period; and cause each Prospectus to be supplemented by any required prospectus supplement, and as so supplemented to be filed pursuant to Rule 424 (or any similar provision then in force) under the Securities Act and comply with the provisions of the Securities Act, the Securities Exchange Act and the rules and regulations thereunder applicable to them with respect to the disposition of all securities covered by each Registration Statement during the applicable period in accordance with the intended method or methods of distribution by the selling Holders thereof (including sales by any Participating Broker-Dealer); provided, however, that nothing contained herein shall imply that the Partnership is liable for any action or inaction of any Holder, including any Participating Broker-Dealer;

(c) in the case of a Shelf Registration, (i) notify each Holder of Registrable Securities, at least three business days prior to filing, that a Shelf Registration Statement (except in the case of an Automatic Shelf Registration Statement, in which case at least three business days prior to the inclusion of information regarding selling security holders in the Prospectus forming a part of such Automatic Shelf Registration Statement) with respect to the Registrable Securities is being filed and advise such Holders that the distribution of Registrable Securities will be made in accordance with the method selected by the Majority Holders participating in the Shelf Registration; (ii) furnish to each Holder of Registrable Securities, if any, without charge, as many copies of each Prospectus, including each preliminary Prospectus, and any amendment or supplement thereto and such other documents as such Holder or underwriter may reasonably request, including financial statements and schedules and, if the Holder so requests, all exhibits in order to facilitate the public sale or other disposition of the Registrable Securities; and (iii) hereby consent to the use of the Prospectus or any amendment or supplement thereto by each of the selling Holders of Registrable Securities in connection with the offering and sale of the Registrable Securities covered by the Prospectus or any amendment or supplement thereto;

(d) in the case of a Shelf Registration, use its commercially reasonable efforts to register or qualify the Registrable Securities under all applicable state securities or blue sky laws of such jurisdictions as any Holder of Registrable Securities covered by a Shelf Registration Statement shall reasonably request by the time the Shelf Registration Statement is declared effective by the

10

SEC or otherwise becomes effective, and do any and all other acts and things which may be reasonably necessary or advisable to enable each such Holder to consummate the disposition in each such jurisdiction of such Registrable Securities owned by such Holder; provided, however, that the Partnership shall not be required to (i) qualify as a foreign limited partnership or as a dealer in securities in any jurisdiction where it would not otherwise be required to qualify but for this Section 3(d), (ii) take any action which would subject it to general service of process or taxation in any such jurisdiction where it is not then so subject or (iii) make any changes to its certificate of incorporation or by-laws (or other organizational documents) or any agreement between it and holders of its ownership interests;

(e) notify promptly counsel for the Holders and counsel for the Dealer Managers and, with respect to clauses (i), (iii), (iv) and (v) of this paragraph only, each Holder of Registrable Securities under a Shelf Registration or any Participating Broker-Dealer who has notified the Partnership that it is utilizing the Exchange Offer Registration Statement as provided in paragraph (f) below and, if requested by such Holder or Participating Broker-Dealer, confirm such advice in writing promptly (i) when a Registration Statement (other than an Automatic Shelf Registration Statement) has become effective and when any post-effective amendments and supplements thereto become effective, (ii) of any request by the SEC or any state securities authority for post-effective amendments and supplements to a Registration Statement and Prospectus or for additional information after the Registration Statement has become effective, (iii) of the issuance by the SEC or any state securities authority of any stop order suspending the effectiveness of a Registration Statement or the initiation of any proceedings for that purpose, (iv) of the happening of any event or the discovery of any facts during the period a Shelf Registration Statement is effective that requires any change in the Registration Statement or Prospectus so that, as of such date, the statements therein are not misleading and do not omit to state a material fact required to be stated therein to make the statements therein not misleading (in the case of the Prospectus, in the light of the circumstances under which they were made); provided, however, that such notice need not identify the event that requires such change, and (v) of the receipt by the Partnership of any notification with respect to the suspension of the qualification of the Registrable Securities or the Exchange Securities, as the case may be, for sale in any jurisdiction or the initiation or threatening of any proceeding for such purpose;

(f) in the case of the Exchange Offer Registration Statement (i) include in the Exchange Offer Registration Statement a section entitled “Plan of Distribution” which section shall be reasonably acceptable to the Dealer Managers on behalf of the Participating Broker-Dealers, and which shall contain a summary statement of the positions taken or policies made by the staff of the SEC with respect to the potential “underwriter” status of any broker-dealer that holds Registrable Securities acquired for its own account as a result of market-making activities or other trading activities and that will be the beneficial owner (as defined in Rule 13d-3 under the Securities Exchange Act) of Exchange Securities to be received by such broker-dealer in the Exchange Offer, whether such positions or policies have been publicly disseminated by the staff of the SEC or such positions or policies, in the reasonable judgment of the Dealer Managers on behalf of the Participating Broker-Dealers and their counsel, represent the prevailing views of the staff of the SEC, including a statement that any such broker-dealer who receives Exchange Securities for Registrable Securities pursuant to the Exchange Offer may be deemed a statutory underwriter and must deliver a prospectus meeting the requirements of the Securities Act in connection with any resale of such Exchange Securities, (ii) furnish to each Participating Broker-

11

Dealer who has delivered to the Partnership the notice referred to in Section 3(e), without charge, as many copies of each Prospectus included in the Exchange Offer Registration Statement, including any preliminary Prospectus, and any amendment or supplement thereto, as such Participating Broker-Dealer may reasonably request, (iii) hereby consent to the use of the Prospectus forming part of the Exchange Offer Registration Statement or any amendment or supplement thereto, by any Person subject to the prospectus delivery requirements of the SEC, including all Participating Broker-Dealers, in connection with the sale or transfer of the Exchange Securities covered by the Prospectus or any amendment or supplement thereto, and (iv) include in documentation to be executed by an exchange offeree in order to participate in the Exchange Offer (x) the following provision:

“If the exchange offeree is a broker-dealer holding Registrable Securities acquired for its own account as a result of market-making activities or other trading activities, it will deliver a prospectus meeting the requirements of the Securities Act in connection with any resale of Exchange Securities received in respect of such Registrable Securities pursuant to the Exchange Offer;” and

(y) a statement to the effect that by a broker-dealer making the acknowledgment described in clause (x) and by delivering a Prospectus in connection with the exchange of Registrable Securities, the broker-dealer will not be deemed to admit that it is an underwriter within the meaning of the Securities Act;

(g) (i) in the case of an Exchange Offer, furnish to counsel for the Dealer Managers and (ii) in the case of a Shelf Registration, furnish to counsel for the Holders copies of any comment letters received from the SEC or any other request by the SEC or any state securities authority for amendments or supplements to a Registration Statement or Prospectus or for additional information;

(h) make every reasonable effort to obtain the withdrawal of any order suspending the effectiveness of a Registration Statement as soon as practicable;

(i) in the case of a Shelf Registration, furnish to each Holder of Registrable Securities upon request, and each underwriter, if any, without charge, at least one conformed copy of each Registration Statement and any post-effective amendment thereto, including financial statements and schedules (without documents incorporated therein by reference and all exhibits thereto, unless requested);

(j) in the case of a Shelf Registration, cooperate with the selling Holders of Registrable Securities to facilitate the timely preparation and delivery of certificates representing Registrable Securities to be sold and not bearing any restrictive legends; and enable such Registrable Securities to be in such denominations (consistent with the provisions of the Indenture) and registered in such names as the selling Holders or the underwriters, if any, may reasonably request at least three business days prior to the closing of any sale of Registrable Securities;

(k) in the case of a Shelf Registration, upon the occurrence of any event or the discovery of any facts, each as contemplated by Section 3(e)(iv), as promptly as practicable after the occurrence of such an event, use its commercially reasonable efforts to prepare a supplement or

12

post-effective amendment to the Registration Statement or the related Prospectus or any document incorporated therein by reference or file any other required document so that, as thereafter delivered to the purchasers of the Registrable Securities or Participating Broker-Dealers, such Prospectus will not contain at the time of such delivery an untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading; at such time as such public disclosure is otherwise made or the Partnership determines that such disclosure is not necessary, in each case to correct any misstatement of a material fact or to include any omitted material fact, the Partnership agrees promptly to notify each Holder of such determination and to furnish to each Holder such number of copies of the Prospectus, as amended or supplemented, as such Holder may reasonably request;

(l) obtain a CUSIP number for each Series of Exchange Securities not later than the effective date of a Registration Statement, and provide the Trustee with printed certificates for each Series of Exchange Securities or each Series of Registrable Securities, as the case may be, in a form eligible for deposit with the Depositary;

(m) unless the Indenture has been qualified under the Trust Indenture Act, (i) cause the Indenture to be qualified under the Trust Indenture Act in connection with the registration of the Exchange Securities or Registrable Securities, as the case may be, (ii) cooperate with the Trustee and the Holders to effect such changes to the Indenture as may be required for the Indenture to be so qualified in accordance with the terms of the Trust Indenture Act and (iii) execute, and use its commercially reasonable efforts to cause the Trustee to execute, all documents as may be required to effect such changes, and all other forms and documents required to be filed with the SEC to enable the Indenture to be so qualified in a timely manner;

(n) in the case of a Shelf Registration, enter into agreements (including, if requested, an underwriting agreement in customary form containing customary representations, warranties, terms and conditions; provided, that the Partnership shall not be required to enter into such agreement more than once with respect to each Series of Registrable Securities and may delay entering into such agreement until the consummation of any underwritten public offering of debt securities which the Partnership may have then undertaken) and take all other customary and appropriate actions in order to expedite or facilitate the disposition of such Registrable Securities and in such connection whether or not an underwriting agreement is entered into and whether or not the registration is an underwritten registration;

(o) in the case of a Shelf Registration or if a Prospectus is required to be delivered by any Participating Broker-Dealer in the case of an Exchange Offer, make available for inspection by a representative of the Holders of the Registrable Securities, any underwriters participating in any disposition pursuant to a Shelf Registration Statement, any Participating Broker-Dealer and counsel for the Holders, all relevant financial and other records, pertinent corporate documents and properties of the Partnership reasonably requested by any such Persons, and use commercially reasonable efforts to have the respective officers, directors, employees and any other agents of the Partnership supply all relevant information reasonably requested by any such representative, underwriter, Participating Broker-Dealer or counsel for the Holders in connection with a Registration Statement, in each case, as is customary for similar due diligence investigations; provided, however, that any information that is designated in writing by the

13

Partnership, in good faith, as confidential at the time of delivery of such information shall be kept confidential by the Holders, any underwriter, any Participating Broker-Dealer and any of their respective representatives, unless such disclosure is made in connection with a court proceeding or required by law, or such information becomes available to the public generally or through a third party without an accompanying obligation of confidentiality; provided, further, that prior notice shall be provided as practicable to the Partnership of the potential disclosure of any information in connection with a court proceeding or required by law to permit the Partnership to obtain a protective order or take such other action to prevent disclosure of such information;

(p) a reasonable time prior to the filing of any Exchange Offer Registration Statement or Shelf Registration Statement (other than an Automatic Shelf Registration Statement), any Prospectus forming a part thereof or of any other Prospectus covering Registrable Securities, any amendment to an Exchange Offer Registration Statement or Shelf Registration Statement or amendment or supplement to such Prospectus (other than with respect to any such amendment or supplement resulting solely from the incorporation by reference of any report filed under the Securities Exchange Act), provide copies of such document to the Dealer Managers, counsel for the Holders, if any, and make such changes in any Exchange Offer Registration Statement, Shelf Registration Statement, any such Prospectus or amendment or supplement thereto prior to the filing thereof as counsel for the Holders may reasonably request within three business days of being sent a draft thereof and make the representatives of the Partnership available for discussion of such documents as shall be reasonably requested by the Dealer Managers;

(q) in the case of a Shelf Registration, use its commercially reasonable efforts to cause the Registrable Securities to be rated by the appropriate rating agencies, if so requested by the Majority Holders, or if requested by the underwriter or underwriters of an underwritten offering of Registrable Securities, if any;

(r) otherwise comply with all applicable rules and regulations of the SEC and make available to its security holders, as soon as reasonably practicable, an earnings statement covering at least 12 months which shall satisfy the provisions of Section 11(a) of the Securities Act and Rule 158 thereunder; and

(s) cooperate and assist in any filings required to be made with FINRA.

In the case of a Shelf Registration Statement, the Partnership may (as a condition to the participation of such Holder and the beneficial owner of Registrable Securities in the Shelf Registration and in addition to any other conditions to such participation set forth in this Agreement) require each Holder of Registrable Securities to furnish to the Partnership prior to the 30th day following the Partnership’s filing of such request for information with the Trustee for delivery to the Holders such information regarding the Holder and the proposed distribution by such Holder or beneficial owner of such Registrable Securities as the Partnership may from time to time reasonably request in writing.

14

In the case of a Shelf Registration Statement, each Holder agrees that, upon receipt of any notice from the Partnership of the happening of any event or the discovery of any facts, each of the kind described in Section 3(e)(iv), such Holder will forthwith discontinue disposition of Registrable Securities pursuant to a Registration Statement until such Holder’s receipt of the copies of the supplemented or amended Prospectus contemplated by Section 3(k), and, if so directed by the Partnership, such Holder will deliver to the Partnership (at its expense) all copies in such Holder’s possession, other than permanent file copies then in such Holder’s possession, of the Prospectus covering such Registrable Securities current at the time of receipt of such notice.

If any of the Registrable Securities covered by any Shelf Registration Statement are to be sold in an underwritten offering, the underwriter or underwriters and manager or managers that will manage such offering will be selected by the Majority Holders of such Registrable Securities included in such offering and shall be acceptable to the Partnership. No Holder of Registrable Securities may participate in any underwritten offering hereunder unless such Holder (a) agrees to sell such Holder’s Registrable Securities on the basis provided in any underwriting arrangements approved by the Persons entitled hereunder to approve such arrangements and (b) completes and executes all questionnaires, powers of attorney, indemnities, underwriting agreements and other documents required under the terms of such underwriting arrangements.

4. Indemnification; Contribution.

(a) The Partnership and the General Partner agree to indemnify and hold harmless each Holder (including the Dealer Managers, if applicable, and each Participating Broker-Dealer) and each Person, if any, who controls any Holder within the meaning of Section 15 of the Securities Act or Section 20 of the Securities Exchange Act as follows:

(i) against any and all loss, liability, claim, damage and expense, as incurred, arising out of any untrue statement or alleged untrue statement of a material fact contained in any Registration Statement pursuant to which Registrable Securities were registered under the Securities Act or the omission or alleged omission therefrom of a material fact required to be stated therein or necessary to make the statements therein not misleading, or arising out of any untrue statement or alleged untrue statement of a material fact contained in any Prospectus or the omission or alleged omission therefrom of a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading;

(ii) against any and all loss, liability, claim, damage and expense, as incurred, to the extent of the aggregate amount paid in settlement of any litigation, or any investigation or proceeding by any governmental agency or body, commenced or threatened, or of any claim whatsoever based upon any such untrue statement or omission, or any such alleged untrue statement or omission; provided, that any such settlement is effected with the written consent of the Partnership; and

(iii) against any and all expense, as incurred (including the reasonable fees and disbursements of counsel chosen by any indemnified party), reasonably incurred in investigating, preparing or defending against any litigation, or any investigation or proceeding by any governmental agency or body, commenced or threatened, or any claim whatsoever based upon any such untrue statement or omission, or any such alleged untrue statement or omission, to the extent that any such expense is not paid under subparagraph (i) or (ii) above;

15

provided, however, that this indemnity agreement shall not apply to any loss, liability, claim, damage or expense to the extent arising out of any untrue statement or omission or alleged untrue statement or omission made in reliance upon and in conformity with written information furnished to the Partnership or the General Partner by such Holder or any underwriter expressly for use in a Registration Statement or any Prospectus.

(b) Each Holder severally, but not jointly, agrees to indemnify and hold harmless the Partnership, the General Partner and the other selling Holders, and each of their respective directors and officers, and each Person, if any, who controls the Partnership, the General Partner or any other selling Holder within the meaning of Section 15 of the Securities Act or Section 20 of the Securities Exchange Act, against any and all loss, liability, claim, damage and expense described in the indemnity contained in Section 4(a), as incurred, but only with respect to untrue statements or omissions, or alleged untrue statements or omissions, made in the Shelf Registration Statement or any Prospectus included therein in reliance upon and in conformity with written information with respect to such Holder furnished to the Partnership or the General Partner by such Holder expressly for use in the Shelf Registration Statement or such Prospectus.

(c) Each indemnified party shall give notice as promptly as reasonably practicable to each indemnifying party of any action or proceeding commenced against it in respect of which indemnity may be sought hereunder, but failure so to notify an indemnifying party shall not relieve such indemnifying party from any liability hereunder to the extent it is not materially prejudiced as a result thereof and in any event shall not relieve it from any liability which it may have otherwise than on account of this indemnity agreement; the indemnifying party shall assume the defense of such action or proceeding with counsel reasonably satisfactory to such indemnified party, and shall not be liable to such indemnified party under this Section 4 for any legal expenses subsequently incurred by such indemnified party in connection with the defense thereof. An indemnified party may participate at its own expense in the defense of such action; provided, however, that counsel to the indemnified party shall not (except with the consent of the indemnifying party) also be counsel to the indemnifying party. In no event shall the indemnifying party or parties be liable for the fees and expenses of more than one counsel (in addition to any local counsel) separate from their own counsel for all indemnified parties in connection with any one action or separate but similar or related actions in the same jurisdiction arising out of the same general allegations or circumstances. No indemnifying party shall, without the prior written consent of the indemnified parties, settle or compromise or consent to the entry of any judgment with respect to any litigation, or any investigation or proceeding by any governmental agency or body, commenced or threatened, or any claim whatsoever in respect of which indemnification or contribution could be sought under this Section 4 (whether or not the indemnified parties are actual or potential parties thereto), unless such settlement, compromise or consent (i) includes an unconditional release of each indemnified party from all liability arising out of such litigation, investigation, proceeding or claim and (ii) does not include a statement as to or an admission of fault, culpability or a failure to act by or on behalf of any indemnified party.

16

(d) If the indemnification provided for in this Section 4 is for any reason unavailable to or insufficient to hold harmless an indemnified party in respect of any losses, liabilities, claims, damages or expenses referred to therein, then each indemnifying party shall contribute to the aggregate amount of such losses, liabilities, claims, damages and expenses incurred by such indemnified party, as incurred, in such proportion as is appropriate to reflect the relative fault of the Partnership or the General Partner on the one hand and the Holders on the other hand in connection with the statements or omissions which resulted in such losses, liabilities, claims, damages or expenses, and the relative benefit received by the indemnified party, on the one hand, and the indemnifying party, on the other hand, in connection with the Exchange Offer and the Shelf Registration, as well as any other relevant equitable considerations.

The relative fault of the Partnership or the General Partner on the one hand and the Holders on the other hand shall be determined by reference to, among other things, whether any such untrue or alleged untrue statement of a material fact or omission or alleged omission to state a material fact relates to information supplied by the Partnership or the Holders and the parties’ relative intent, knowledge, access to information and opportunity to correct or prevent such statement or omission.

The Partnership, the General Partner and the Holders agree that it would not be just and equitable if contribution pursuant to this Section 4 were determined by pro rata allocation or by any other method of allocation which does not take account of the equitable considerations referred to above in this Section 4. The aggregate amount of losses, liabilities, claims, damages and expenses incurred by an indemnified party and referred to above in this Section 4 shall be deemed to include any legal or other expenses reasonably incurred by such indemnified party in investigating, preparing or defending against any litigation, or any investigation or proceeding by any governmental agency or body, commenced or threatened, or any claim whatsoever based upon any such untrue or alleged untrue statement or omission or alleged omission.

No Person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Securities Act) shall be entitled to contribution from any Person who was not guilty of such fraudulent misrepresentation.

For purposes of this Section 4, each Person, if any, who controls a Holder within the meaning of Section 15 of the Securities Act or Section 20 of the Securities Exchange Act shall have the same rights to contribution as such Holder, and each director of the Partnership or the General Partner, and each Person, if any, who controls the Partnership or the General Partner within the meaning of Section 15 of the Securities Act or Section 20 of the Securities Exchange Act shall have the same rights to contribution as the Partnership or the General Partner, respectively.

5. Miscellaneous.

5.1. No Inconsistent Agreements. The Partnership has not entered into and the Partnership will not after the date of this Agreement enter into any agreement which is inconsistent with the rights granted to the Holders of Registrable Securities in this Agreement or otherwise conflicts with the provisions hereof. The rights granted to the Holders hereunder do not and will not for the term of this Agreement in any way conflict with the rights granted to the holders of the Partnership’s other issued and outstanding securities under any such agreements.

17

5.2. Amendments and Waivers. The provisions of this Agreement, including the provisions of this sentence, may not be amended, modified or supplemented, and waivers or consents to departures from the provisions hereof may not be given unless the Partnership has obtained the written consent of Holders of at least a majority in aggregate principal amount of the outstanding Registrable Securities affected by such amendment, modification, supplement, waiver or departure.

5.3. Notices. All notices and other communications provided for or permitted hereunder shall be made in writing by hand delivery, registered first-class mail, telex, telecopier, or any courier guaranteeing overnight delivery (a) if to a Holder, at the most current address given by such Holder to the Partnership by means of a notice given in accordance with the provisions of this Section 5.3, which address initially is the address set forth in the Dealer Manager Agreement with respect to the Dealer Managers; and (b) if to the Partnership, initially at the Partnership’s address set forth in the Dealer Manager Agreement, and thereafter at such other address of which notice is given in accordance with the provisions of this Section 5.3.

All such notices and communications shall be deemed to have been duly given: at the time delivered by hand, if personally delivered; two business days after being deposited in the mail, postage prepaid, if mailed; when answered back, if telexed; when receipt is acknowledged, if telecopied; and on the next business day if timely delivered to an air courier guaranteeing overnight delivery.

Copies of all such notices, demands or other communications shall be concurrently delivered by the Person giving the same to the Trustee under the Indenture, at the address specified in such Indenture.

5.4. Successor and Assigns. This Agreement shall inure to the benefit of and be binding upon the successors, assigns and transferees of each of the parties, including, without limitation and without the need for an express assignment, subsequent Holders; provided, however, that nothing herein shall be deemed to permit any assignment, transfer or other disposition of Registrable Securities in violation of the terms of the Dealer Manager Agreement, any note or global note representing such Registrable Securities or the Indenture. If any transferee of any Holder shall acquire Registrable Securities, in any manner, whether by operation of law or otherwise, such Registrable Securities shall be held subject to all of the terms of this Agreement, and by taking and holding such Registrable Securities such Person shall be conclusively deemed to have agreed to be bound by and to perform all of the terms and provisions of this Agreement, including the restrictions on resale set forth in this Agreement and, if applicable, the Dealer Manager Agreement, and such person shall be entitled to receive the benefits hereof.

5.5. Third Party Beneficiaries. The Dealer Managers (even if each Dealer Manager is not a Holder of Registrable Securities) shall be a third party beneficiary to the agreements made hereunder by the Partnership for the benefit of the Holders and shall have the right to enforce such agreements directly to the extent it deems such enforcement necessary or advisable to protect its rights or the rights of Holders hereunder. Each Holder of Registrable Securities shall

18

be a third party beneficiary to the agreements made hereunder between the Partnership, on the one hand, and the Dealer Managers, on the other hand, and shall have the right to enforce such agreements directly to the extent it deems such enforcement necessary or advisable to protect its rights hereunder.

5.6. Restriction on Resales. Until the expiration of one year after the original issuance of the New MPLX Notes, the Partnership will not, and will cause its “affiliates” (as such term is defined in Rule 144(a)(1) under the Securities Act) not to, resell any New MPLX Notes which are “restricted securities” (as such term is defined in Rule 144(a)(3) under the Securities Act) that have been reacquired by any of them and shall immediately upon any purchase of any such New MPLX Notes submit such to the Trustee for cancellation.

5.7. Counterparts. This Agreement may be executed in any number of counterparts and by the parties hereto in separate counterparts, each of which when so executed shall be deemed to be an original and all of which taken together shall constitute one and the same agreement.

5.8. Headings. The headings in this Agreement are for convenience of reference only and shall not limit or otherwise affect the meaning hereof.

5.9. GOVERNING LAW. THIS AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAW OF THE STATE OF NEW YORK WITHOUT REGARD TO THE PRINCIPLES OF CONFLICT OF LAWS THEREOF.

5.10. Severability. In the event that any one or more of the provisions contained herein, or the application thereof in any circumstance, is held invalid, illegal or unenforceable, the validity, legality and enforceability of any such provision in every other respect and of the remaining provisions contained herein shall not be affected or impaired thereby.

[Signature Pages Follow]

19

IN WITNESS WHEREOF, the parties have executed this Agreement as of the date first written above.

[Signature Page to Registration Rights Agreement]

Confirmed and accepted as of the date first above written:

[Signature Page to Registration Rights Agreement]

Confirmed and accepted as of the date first above written:

[Signature Page to Registration Rights Agreement]

Confirmed and accepted as of the date first above written:

[Signature Page to Registration Rights Agreement]