EXHIBIT 4.1

SIXTH SUPPLEMENTAL INDENTURE

THIS SIXTH SUPPLEMENTAL INDENTURE dated as of May 1, 2006 (this "Supplemental Indenture"), among Pioneer Natural Resources Company, a Delaware corporation (the "Company"), Pioneer Natural Resources USA, Inc., a Delaware corporation, for purposes of agreeing to make certain guarantees pursuant to
Section 3 hereof (the "Guarantor"), and The Bank of New York Trust Company, N.A., a national banking association organized under the laws of the United States of America, as successor trustee (the "Trustee"). Capitalized terms used herein and not otherwise defined have the meanings set forth in the Indenture referred to below.

RECITALS

A. The Company and The Bank of New York, a New York banking corporation (the "Prior Trustee"), entered into that certain Indenture, dated as of January 13, 1998 (the "Indenture"), pursuant to which the Company may from time to time issue its debentures, notes, bonds or other evidences of indebtedness (collectively, the "Debt Securities").

B. The Company, the Prior Trustee and the Trustee are parties to that certain Agreement of Resignation, Appointment and Acceptance, dated as of February 21, 2005, pursuant to which the Prior Trustee resigned as trustee under the Indenture and the Trustee was appointed as successor trustee under the Indenture.

C. Article IX of the Indenture provides that the Company, when authorized by a resolution of the Board of Directors of the Company, and the Trustee may, without the consent of the holders of the Debt Securities, enter into a supplemental indenture to establish the form or terms of Debt Securities of any series as permitted by Sections 2.01 and 2.03 of the Indenture.

D. The Company desires to issue, and upon certain events specified in this Supplemental Indenture, the Guarantor desires to agree to be obligated to guarantee, $450,000,000 aggregate principal amount of 6.875% Senior Notes due 2018 (the "Notes") and in connection therewith, the Company and the Guarantor have duly determined to make, execute and deliver to the Trustee this Supplemental Indenture to set forth the terms and provisions of the Notes as required by the Indenture.

NOW, THEREFORE, in consideration of the mutual agreements and covenants set forth herein, the parties hereto agree, subject to the terms and conditions hereinafter set forth, as follows for the benefit of the Trustee and the Holders of the Notes:

Section 1. Notes. Pursuant to Section 2.03 of the Indenture, the terms and provisions of the Notes are as follows:

(a) The title of the Notes shall be "6.875% Senior Notes due 2018."

(b) The Notes shall be initially limited to $450,000,000 aggregate principal amount. The Company may, without the consent of the Holders of the Notes, increase such aggregate principal amount in the future, on the same terms and conditions and with the same CUSIP numbers as the Notes. The Company shall

not issue any such additional Notes unless the additional Notes are fungible with the Notes for United States federal income tax purposes.

(c) The Notes shall not require any principal or premium payments prior to maturity on May 1, 2018.

(d) The rate at which the Notes shall bear interest shall be 6.875% per annum; interest on the notes shall accrue from May 1, 2006, for the first interest payment and from the most recent interest payment date thereafter; the interest payment dates on which such interest shall be payable shall be May 1 and November 1, beginning November 1, 2006; and the record dates for the determination of the holders of the Notes to whom such interest is payable shall be the immediately preceding April 15 (for May 1 payment dates) and October 15 (for November 1 payment dates); the rate at which the overdue principal shall bear interest shall be 1% per annum in excess of the rate stated initially in this clause; and the rate at which overdue installments of interest shall bear interest shall be 1% per annum in excess of the rate stated initially in this clause to the extent lawful.

(e) Payments of principal of and interest on the Notes represented by one or more Global Senior Notes initially registered in the name of The Depository Trust Company (the "Depositary") or its nominee with respect to the Notes shall be made by the Company through the Trustee in immediately available funds to the Depositary or its nominee, as the case may be.

(f) The Notes shall be redeemable at any time, at the option of the Company, in whole or from time to time in part, at the price, and otherwise in accordance with the terms and provisions, set forth in Section 2 of this Supplemental Indenture and (to the extent they do not conflict with Section 2 of this Supplemental Indenture) the terms and provisions of Sections 3.03 and 3.04 of the Indenture.

(g) The Notes shall be represented by one or more Global Senior Notes deposited with the Depositary and registered in the name of the nominee of the Depositary.

(h) There shall be no mandatory sinking fund for the payments of the Notes.

(i) As long as the Depositary or its nominee, or a successor Depositary or its nominee, is the registered owner of the Global Senior Notes relating to the Notes, owners of the beneficial interests in such Global Senior Notes shall not be entitled to have the Notes registered in their names and shall not receive or be entitled to receive physical delivery of Notes in definitive form except (i) as provided in Section 2.15(c) of the Indenture or (ii) if an Event of Default with respect to the Notes has occurred and is continuing.

(j) The Bank of New York Trust Company, N.A. shall be the Trustee for the Notes under the Indenture.

(k) Article X of the Indenture shall apply to the Notes.

(l) The Notes shall not be subordinated pursuant to the provisions of Article XII of the Indenture. The Notes shall be senior unsecured obligations of the Company ranking pari passu with other existing and future senior unsecured indebtedness of the Company.

(m) The Company shall be subject to all the covenants set forth in Article IV of the Indenture with respect to the Notes.

(n) To the extent not set forth herein, the provisions of Section 2.03 of the Indenture are not applicable.

Section 2. Optional Redemption of Notes. The Notes will be redeemable at any time, at the option of the Company, in whole or from time to time in part, upon not less than 30 and not more than 60 days' notice as provided in the Indenture, on any date prior to maturity (the "Redemption Date") at a price equal to 100% of the principal amount thereof plus accrued and unpaid interest, if any, to the Redemption Date (subject to the right of Holders of record on the relevant record date to receive interest due on any interest payment date that is on or prior to the Redemption Date) plus a Make-Whole Premium, if any (the "Redemption Price"). In no event will a Redemption Price ever be less than 100% of the principal amount of the Notes plus accrued and unpaid interest, if any, to the Redemption Date.

The amount of the Make-Whole Premium with respect to any of the Notes (or portion thereof) to be redeemed will be equal to the excess, if any, of:

(a) the sum of the present values, calculated as of the Redemption Date, of:

(i) each interest payment that, but for such redemption, would have been payable on such Note (or portion thereof) being redeemed on each interest payment date occurring after the Redemption Date (excluding any accrued interest for the period prior to the Redemption Date); and

(ii) the principal amount that, but for such redemption, would have been payable at the final maturity of such Note (or portion thereof) being redeemed; over

(b) the principal amount of such Note (or portion thereof) being redeemed.

The present values of interest and principal payments referred to in clause
(a) above will be determined in accordance with generally accepted principles of financial analysis. Such present values will be calculated by discounting the amount of each payment of interest or principal from the date that each such payment would have been payable, but for the redemption, to the Redemption Date at a discount rate equal to the Treasury Yield (as defined below) plus 50 basis points.

The Make-Whole Premium will be calculated by an independent investment banking institution of national standing appointed by the Company; provided that if the Company fails to make such appointment at least 45 business days prior to the Redemption Date, or if the institution so appointed is unwilling or unable to make such calculation, such calculation will be made by an independent investment banking institution of national standing appointed by the Trustee (in any such case, an "Independent Investment Banker").

For purposes of determining the Make-Whole Premium, "Treasury Yield" means a rate of interest per annum equal to the weekly average yield to maturity of United States Treasury Notes that have a constant maturity that corresponds to

the remaining term to maturity of the applicable Notes, calculated to the nearest 1/12th of a year (the "Remaining Term"). The Treasury Yield will be determined as of the third business day immediately preceding the applicable Redemption Date.

The weekly average yields of United States Treasury Notes will be determined by reference to the most recent statistical release published by the Federal Reserve Bank of New York and designated "H.15 (519) Selected Interest Rates" or any successor release (the "H.15 Statistical Release"). If the H.15 Statistical Release sets forth a weekly average yield for United States Treasury Notes having a constant maturity that is the same as the Remaining Term, then the Treasury Yield will be equal to such weekly average yield. In all other cases, the Treasury Yield will be calculated by interpolation, on a straight-line basis, between the weekly average yields on the United States Treasury Notes that have a constant maturity closest to and greater than the Remaining Term and the United States Treasury Notes that have a constant maturity closest to and less than the Remaining Term (in each case as set forth in the H.15 Statistical Release). Any weekly average yields so calculated by interpolation will be rounded to the nearest 1/100th of 1%, with any figure of 1/200th of 1% or above being rounded upward. If weekly average yields for United States Treasury Notes are not available in the H.15 Statistical Release or otherwise, then the Treasury Yield will be calculated by interpolation of comparable rates selected by the Independent Investment Banker.

In the case of any partial redemption, selection of the Notes for redemption will be made by the Trustee on a pro rata basis, by lot or by such other method as the Trustee in its sole discretion shall deem to be fair and appropriate, although no such Note of $1,000 in original principal amount or less shall be redeemed in part. If any Note is to be redeemed in part only, the notice of redemption relating to such Note shall state the portion of the principal amount thereof to be redeemed. A new Note in principal amount equal to the unredeemed portion thereof will be issued in the name of the Holder thereof upon cancellation of the original Note.

Section 3. Obligation to Guarantee. If at any time any of the Company's 8 1/4% Senior Notes due 2007, 6.50% Senior Notes due 2008, 5.875% Senior Notes due 2012, 5.875% Senior Notes due 2016 or 7.20% Senior Notes due 2028 (the "7.20% Notes," and collectively with all other senior notes, the "Other Senior Notes") are guaranteed by the Guarantor pursuant to the terms of the Indenture or any applicable supplemental indenture related to such senior notes, then the Company, the Guarantor and the Trustee shall as soon as reasonably practicable thereafter execute and deliver a supplemental indenture to the Indenture pursuant to which the Guarantor shall unconditionally guarantee the Notes on substantially the same terms as the Guarantor shall have guaranteed the 7.20% Notes; provided, however, that if the Guarantor is not required to guarantee the 7.20% Notes or if the 7.20% Notes are no longer outstanding, then the Guarantor shall guarantee the Notes on substantially the same terms as the most recently issued series of Other Senior Notes that are guaranteed. The Company, the Guarantor and the Trustee, as applicable, also shall execute and deliver such other documents, instruments or certificates as are reasonably necessary or appropriate to effect the required guarantee of the Notes.

Section 4. Amendments to Sections 1.01, 2.07 and 2.15 and Article IV.

(a) Section 1.01. Section 1.01 is hereby amended, solely with respect to the Notes, by:

(i) deleting clause (a)(iv)(A) of the definition of "Adjusted Consolidated Net Tangible Assets" and substituting therefor the following language "the net book value of other tangible assets of the Company and its Subsidiaries, as of a date no earlier than the date of the Company's latest annual or quarterly financial statement, and"; deleting the following language "Issue Date (including, without limitation, under the Credit Agreements)" at the end of clause (e) of the definition of "Permitted Liens" and substituting therefor the following language "date on which the 6.875% Senior Notes due 2018 of the Company were originally issued"; adding the following language "and Liens securing Non-Recourse Indebtedness; provided, however, that the related purchase money Indebtedness and Non-Recourse Indebtedness, as applicable, shall not be secured by any Property or assets of the company or any Restricted Subsidiary other than the Property acquired by the Company with the proceeds of such purchase money Indebtedness or Non-Recourse Indebtedness, as applicable" after "Purchase Money Liens" in clause (i) of the definition of "Permitted Liens";

(ii) deleting the definition of "Credit Agreements" and substituting therefor the definition "Credit Facility" as follows:

"Credit Facility" means, with respect to the Company, the credit facility made available to the Company pursuant to the Amended and Restated 5-Year Revolving Credit Agreement dated as of September 30, 2005, among the Company and the lenders named therein, together with any Refinancings thereof by a lender or a syndicate of lenders. It is understood and agreed that the Credit Facility may be refinanced, refunded, extended, renewed or replaced (through one or more such refinancings, refundings, extensions, renewals or replacements), as a whole, or in part, from time to time after the termination of the applicable Credit Facility."; and

(iii) adding a definition of "Refinance" as follows:

"Refinance" means, in respect of any Indebtedness, to refinance, extend, renew, refund, repay, prepay, redeem, defease or retire, or to issue other Indebtedness in exchange or replacement for, such indebtedness. "Refinanced" and "Refinancing" shall have correlative meanings.

(iv) adding a definition of "Non-Recourse Indebtedness" as follows:

"Non-Recourse Indebtedness" means Indebtedness or that portion of Indebtedness of the Company incurred in connection with the acquisition by the Company of any Property and as to which:

(1) the holders of such Indebtedness agree in writing that they will look solely to the Property so acquired and securing such Indebtedness for payment on or in respect of such Indebtedness and

(2) no default with respect to such Indebtedness would permit (after notice or passage of time or both), according to the terms of any other Indebtedness of the Company or a Restricted Subsidiary, any holder of such other Indebtedness to declare a default under such other Indebtedness or cause the payment of such other Indebtedness to be accelerated or payable prior to its stated maturity.

(b) Sections 2.07. Section 2.07 is hereby amended, solely with respect to the Notes, by adding "the Underwriters," before "the Company" in the last sentence of Section 2.07.

(c) Sections 2.15. Section 2.15 is hereby amended, solely with respect to the Notes, by adding "the Underwriters," before "the Company" in the third sentence of subclause (v) of Section 2.15(c).

Section 5. Ratification. This Supplemental Indenture is executed and shall be construed as an indenture supplemental to the Indenture and, as provided in the Indenture, this Supplemental Indenture forms a part of the Indenture. Except to the extent amended by or supplemented by this Supplemental Indenture, the Company, the Guarantor and the Trustee hereby ratify, confirm and reaffirm the Indenture in all respects.

Section 6. Counterparts. This Supplemental Indenture may be executed in any number of counterparts, each of which so executed shall be an original, but all such counterparts shall together constitute but one and the same instrument.

Section 7. Governing Law. The laws of the State of New York shall govern the construction and interpretation of this Supplemental Indenture, without regard to principles of conflicts of laws.

Section 8. Trustee Not Responsible for Recitals or Issuance of Notes. The recitals contained herein and in the Notes, except the Trustee's certificates of authentication, shall be taken as the statements of the Company, 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. The Trustee shall not be accountable for the use or application by the Company of Notes or the proceeds thereof.

[Signature Page Follows]

IN WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture to be signed on their behalf by their duly authorized representatives as of the date first above written:

Pioneer Natural Resources Company

By:  /s/ Richard P. Dealy
     ------------------------------------
Name:  Richard P. Dealy
Title: Executive Vice President and
       Chief Financial Officer

Pioneer Natural Resources USA, Inc.

By:  /s/ Richard P. Dealy
     ------------------------------------
Name:  Richard P. Dealy
Title: Executive Vice President and
       Chief Financial Officer

The Bank of New York Trust Company, N.A., as Trustee

By:  /s/ John C. Stohlmann
     ------------------------------------
Name:  John C. Stohlmann
Title: Vice President

EXHIBIT 4.2

UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITARY TRUST COMPANY, A NEW YORK CORPORATION ("DTC"), NEW YORK, NEW YORK, TO THE COMPANY 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 ON THE REVERSE HEREOF.

[FACE OF SECURITY]

CUSIP NO. 723787 AF 4

No. T-01 $450,000,000

6.875% Senior Notes due 2018

Pioneer Natural Resources Company, a Delaware corporation, promises to pay to Cede & Co., or registered assigns, the principal sum of $450,000,000 Dollars on May 1, 2018.

Interest Payment Dates: May 1 and November 1 Record Dates: April 15 and October 15

Additional provisions of this Security are set forth on the other side of this Security.

Dated: May 1, 2006

PIONEER NATURAL RESOURCES COMPANY

By: /s/ Richard P. Dealy
    ---------------------------------
    Richard P. Dealy
    Executive Vice President and
    Chief Financial Officer



By: /s/ Mark H. Kleinman
    ----------------------------------
    Mark H. Kleinman
    Secretary

TRUSTEE'S CERTIFICATE OF AUTHENTICATION

THE BANK OF NEW YORK TRUST COMPANY, N.A., as Trustee, certifies that this is one of the Debt Securities, designated 6.875% Senior Notes due 2018, referred to in the Indenture.

By: /s/ John C. Stohlmann
    ----------------------------------
    Authorized Signatory

[REVERSE OF SECURITY]

6.875% Senior Notes due 2018

1. Interest

Pioneer Natural Resources Company, a Delaware corporation (such corporation, and its successors and assigns under the Indenture hereinafter referred to, being herein called the "Company"), promises to pay interest on the principal amount of this Security at the rate per annum shown above. The Company shall pay interest semiannually on May 1 and November 1 of each year commencing on November 1, 2006. Interest on the Securities shall accrue from the most recent date to which interest has been paid or, if no interest has been paid, from May 1, 2006. Interest shall be computed on the basis of a 360-day year of twelve 30-day months. The Company shall pay interest on overdue principal at 1% per annum in excess of the rate borne by the Securities, and it shall pay interest on overdue installments of interest at such higher rate to the extent lawful.

2. Method of Payment

The Company shall pay interest on the Securities (except defaulted interest) to the Persons who are registered holders of Securities at the close of business on the April 15 or October 15 next preceding the interest payment date even if Securities are canceled after the record date and on or before the interest payment date. Holders must surrender Securities to a Paying Agent to collect principal payments. The Company shall pay principal and interest in immediately available (same day) funds in money of the United States of America that at the time of payment is legal tender for payment of public and private debts. However, the Company may pay principal and interest by check or wire transfer payable in immediately available (same day) funds in such money.

3. Paying Agent and Registrar

Initially, The Bank of New York Trust Company, N.A., a United States banking association ("Trustee"), shall act as Paying Agent and Registrar. The Company may appoint and change any Paying Agent, Registrar or co-registrar without notice. The Company or any of its domestically incorporated wholly owned Subsidiaries may act as paying agent, Registrar or co-registrar.

4. Indenture

The Company issued the Securities under an indenture dated as of January 13, 1998, between the Company and the Trustee, as supplemented by the sixth supplemental indenture dated as of May 1, 2006 (the "Sixth Supplemental Indenture," and, collectively with the aforementioned indenture, the "Indenture"), among the Company, Pioneer Natural Resources USA, Inc., a Delaware corporation (the "Guarantor"), and the Trustee. The terms of the Securities include those stated in the Indenture and those made part of the Indenture by reference to the Trust Indenture Act of 1939 (15 U.S.C. Sec. 77aaa-77bbbb) as in effect on the date of the Indenture (the "Act"). Terms defined in the Indenture and not defined herein have the meanings ascribed thereto in the Indenture. The

Securities are subject to all such terms, and Holders are referred to the Indenture and the Act for a statement of those terms.

This Security is one of a duly authorized issue of general unsecured obligations of the Company all issued or to be issued under the Indenture. Debt Securities issued under the Indenture may be issued in one or more series, which different series may be issued in various aggregate principal amounts, may mature at different times, may bear interest at different rates, may have different conversion prices (if any), may be subject to different redemption provisions, may be subject to different sinking, purchase or analogous funds, may be subject to different covenants, Events of Default and subordination provisions and may otherwise vary as the Indenture provides. This Security is one of a series designated as 6.875% Senior Notes due 2018 (the "Securities") issued under the Indenture, limited to $450,000,000 aggregate principal amount. The Company may, without the consent of the Holders of the Notes, increase such aggregate principal amount in the future, on the same terms and conditions and with the same CUSIP numbers as the Notes. The Company shall not issue any such additional Notes unless the additional Notes are fungible with the Notes for United States federal income tax purposes. The Indenture imposes certain limitations (with significant exceptions) on the ability of the Company and its Subsidiaries to create Liens on assets and engage in sale and leaseback transactions. This Indenture also imposes limitations on the ability of the Company to consolidate, merge or transfer all or substantially all of its assets.

5. Obligation to Guarantee

The Guarantor, pursuant to the Sixth Supplemental Indenture, has agreed that, if any of certain other senior notes of the Company hereafter are guaranteed by the Guarantor then, it will at that time unconditionally guarantee
(a) the due and punctual payment of the principal of, premium, if any, and interest on the Securities, whether at the maturity date, by acceleration or otherwise, and of interest on the overdue principal of and interest, if any, on any premium and interest of the Securities and all other obligations of the Company to the Holders or the Trustee under the Indenture or the Securities and
(b) in case of any extension of time of payment or renewal of any Securities or any of such other obligations, that the same will be promptly paid in full when due or performed in accordance with the terms of the extension or renewal, whether at stated maturity, by acceleration or otherwise.

The obligations of the Guarantor to the Holders and to the Trustee are as expressly set forth in Section 3 of the Sixth Supplemental Indenture and in such other provisions of the Indenture as are applicable to the Guarantor, and reference is hereby made to such Indenture for the precise terms of this obligation to guarantee. The terms of Section 3 of the Sixth Supplemental Indenture and such other provisions of the Indenture as are applicable to the Guarantor are incorporated herein by reference.

6. Optional Redemption

The Securities will be redeemable at any time, at the option of the Company, in whole or from time to time in part, upon not less than 30 and not more than 60 days' notice as provided in the Indenture, on any date prior to their maturity (the "Redemption Date") at a price equal to 100% of the principal amount thereof plus accrued and unpaid interest, if any, to the Redemption Date

(subject to the right of Holders of record on the relevant record date to receive interest due on an interest payment date that is on or prior to the Redemption Date) plus a Make-Whole Premium, if any, calculated as provided in
Section 2 of the Sixth Supplemental Indenture (the "Redemption Price"). In no event will a Redemption Price ever be less than 100% of the principal amount of the Securities plus accrued and unpaid interest, if any, to the Redemption Date.

7. Denominations; Transfer; Exchange

The Securities are in registered form without coupons in denominations of $1,000 and whole multiples of $1,000. A Holder may transfer or exchange Securities only in accordance with the Indenture. The Registrar may require a Holder, among other things, to furnish appropriate endorsements or transfer documents and to pay any taxes and fees required by law or permitted by the Indenture.

8. Persons Deemed Owners

The registered Holder of this Security may be treated as the owner of it for all purposes.

9. Unclaimed Money

If money for the payment of principal or interest remains unclaimed for two years, the Trustee or Paying Agent shall pay the money back to the Company at its request unless an abandoned property law designates another Person. After any such payment, Holders entitled to the money must look only to the Company and not to the Trustee for payment.

10. Discharge and Defeasance

Subject to certain conditions, the Company at any time may terminate some or all its obligations under the Securities and the Indenture if the Company deposits with the Trustee cash or U.S. Government Obligations for the payment of principal and interest on the Securities to redemption or maturity, as the case may be.

11. Amendment, Waiver

Subject to certain exceptions set forth in the Indenture, (i) the Indenture or the Securities may be amended with the written consent of the Holders of at least a majority in principal amount outstanding of the Securities and (ii) any acceleration of principal and interest on the Securities resulting from a default or noncompliance with any provision may be waived with the written consent of the Holders of a majority in principal amount outstanding of the Securities. Subject to certain exceptions set forth in Article IX of the Indenture, without the consent of any Holder, the Company and the Trustee may amend the Indenture or the Securities to cure, among other things, any ambiguity, omission, defect or inconsistency, or to evidence the succession of another Person to the Company pursuant to Article X of the Indenture, or to add guarantees with respect to the Securities or to secure the Securities, or to add additional covenants or surrender rights and powers conferred on the Company, or to permit the qualification of the Indenture under the Act, or to make any change that does not adversely affect the rights of any Holder, or to provide for the acceptance of a successor or separate Trustee.

12. Defaults and Remedies

Under the Indenture, Events of Default include (i) default for 30 days in payment of interest on the Securities; (ii) default in payment of principal or premium on the Securities at maturity, upon acceleration or otherwise; (iii) failure by the Company to comply with other agreements in the Indenture or the Securities, in certain cases subject to notice by Holders and lapse of time;
(iv) certain accelerations (including failure to pay within any grace period after final maturity) of other Indebtedness of the Company or any Subsidiary of the Company if the amount accelerated (or so unpaid) exceeds $20,000,000 and continues for 10 days after the required notice to the Company; (v) certain events of bankruptcy or insolvency with respect to the Company and any Significant Subsidiary; (vi) certain judgments or decrees for the payment of money in excess of $20,000,000 and (vii) failure by the Guarantor to comply with certain agreements in the Sixth Supplemental Indenture. If an Event of Default occurs and is continuing, the Trustee or the Holders of at least 25% in principal amount of the Securities may declare all the Securities to be due and payable immediately. Certain events of bankruptcy or insolvency are Events of Default that will result in the Securities being due and payable immediately upon the occurrence of such Events of Default without any action by the Trustee or any Holders.

Holders may not enforce the Indenture or the Securities except as provided in the Indenture. The Trustee may refuse to enforce the Indenture or the Securities unless it receives reasonable indemnity or security. Subject to certain limitations, Holders of a majority in principal amount of the Securities may direct the Trustee in its exercise of any trust or power. The Trustee may withhold from Holders notice of any continuing Default (except a Default in payment of principal or interest) if it determines that withholding notice is in the interest of the Holders.

13. Trustee Dealings with the Company

Subject to certain limitations imposed by the Act, the Trustee under the Indenture, in its individual or any other capacity, may become the owner or pledgee of Securities and may otherwise deal with and collect obligations owed to it by the Company or its Affiliates and may otherwise deal with the Company or its Affiliates with the same rights it would have if it were not Trustee.

14. No Recourse Against Others

An incorporator and any past, present or future director, officer, employee or stockholder, as such, of the Company shall not have any liability for any obligations of the Company under the Securities or the Indenture or for any claim based on, in respect of or by reason of such obligations or their creation. By accepting a Security, each Holder waives and releases all such liability. The waiver and release are part of the consideration for the issue of the Securities.

15. Authentication

This Security shall not be valid until an authorized signatory of the Trustee (or an authenticating agent) manually signs the certificate of authentication on the other side of this Security.

16. Abbreviations

Customary abbreviations may be used in the name of a Holder 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).

17. Governing Law

THIS SECURITY SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK BUT WITHOUT GIVING EFFECT TO APPLICABLE PRINCIPLES OF CONFLICTS OF LAW TO THE EXTENT THAT THE APPLICATION OF THE LAWS OF ANOTHER JURISDICTION WOULD BE REQUIRED THEREBY.

18. CUSIP Numbers

Pursuant to a recommendation promulgated by the Committee on Uniform Security Identification Procedures the Company has caused CUSIP numbers to be printed on the Securities and has directed the Trustee to use CUSIP numbers in notices of redemption as a convenience to Holders. No representation is made as to the accuracy of such numbers either as printed on the Securities or as contained in any notice of redemption and reliance may be placed only on the other identification numbers placed thereon.

The Company shall furnish to any Holder upon written request and without charge to the Holder a copy of the Indenture that has in it the text of this Security. Requests may be made to:

Corporate Secretary Pioneer Natural Resources Company 5205 North O'Connor Boulevard, Suite 900 Irving, TX 75039

ASSIGNMENT FORM

To assign this Security, fill in the form below:

I or we assign and transfer this Security to

and irrevocably appoint __________________ agent to transfer this Security on the books of the Company. The agent may substitute another to act for him.

Date:                         Your Signature:
     --------------------                     ---------------------------------

                                           (Sign exactly as your name appears on
                                           the other side of the Security)

(Signature must be guaranteed by a member firm of the New York Stock Exchange or a commercial bank or trust company)