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AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON FEBRUARY 16, 2016

REGISTRATION NO. 333-202956

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

POST-EFFECTIVE AMENDMENT NO. 1

to

Form S-3

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

ANDREW E. HARDING

ASSOCIATE GENERAL COUNSEL

UNIT CORPORATION

7130 SOUTH LEWIS, SUITE 1000, TULSA, OKLAHOMA 74136

(918) 493-7700

(Name, address, including zip code, and telephone number, including area code, of agent for service)

WITH COPY TO:

ROBERT J. MELGAARD

JASON B. COUTANT

CONNER & WINTERS, LLP

4000 ONE WILLIAMS CENTER

TULSA, OKLAHOMA 74172

(918) 586-5711

APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC: From time to time after the effective date of this registration statement.

If the only securities being registered on this Form are to be offered under dividend or interest reinvestment plans, please check the following box.   ¨

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis under Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box.   x

If this Form is filed to register additional securities for an offering under Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.   ¨

If this Form is a post-effective amendment filed under Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.   ¨

If this Form is a registration statement under General Instruction I.D. or a post-effective amendment thereto that will become effective on filing with the Commission under Rule 462(e) under the Securities Act, check the following box.   x

If this Form is a post-effective amendment to a registration statement filed under General Instruction I.D. filed to register additional securities or additional classes of securities under Rule 413(b) under the Securities Act, check the following box.   ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act. (Check one):

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Note: Unit Texas Drilling, L.L.C. was originally included as a subsidiary guarantor registrant on this registration statement. Unit Texas Drilling, L.L.C. is not included as a subsidiary guarantor registrant on this post-effective amendment because it has been merged out of existence.

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EXPLANATORY NOTE

This Post-Effective Amendment No. 1 to the Registration Statement on Form S-3 (Commission File No. 333-202956) (the “Registration Statement”) of Unit Corporation (the “Registrant”) is being filed because the Registrant expects that it will no longer be a well-known seasoned issuer (as such term is defined in Rule 405 of the Securities Act of 1933, as amended), when it files its Annual Report on Form 10-K for the fiscal year ended December 31, 2015. This Post-Effective Amendment No. 1 adds disclosure to the Registration Statement required for a registrant other than a well-known seasoned issuer and makes certain other amendments.

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PROSPECTUS

UNIT CORPORATION

$500,000,000

Debt Securities

Preferred Stock

Common Stock

Warrants

Purchase Contracts

Units

By this prospectus, we may offer and sell from time to time:

One or more of our subsidiaries may guarantee the senior or subordinated debt securities offered by this prospectus.

This prospectus provides you with a general description of the securities that may be offered. Each time we offer securities under this prospectus, we will provide you with one or more supplements to this prospectus that will contain additional information about the specific offering. The supplements may also add, update or change information contained in this prospectus. You should read this prospectus and any supplements to this prospectus carefully before you invest in the securities.

Our common stock is listed on the New York Stock Exchange under the symbol “UNT.” Our executive offices are located at 7130 South Lewis, Suite 1000, Tulsa, Oklahoma 74136, and our telephone number is (918) 493-7700.

There are significant risks associated with an investment in our securities. You should read carefully the risks we describe in the accompanying prospectus supplement as well as the risk factors discussed in our periodic reports that we file with the Securities and Exchange Commission (the “SEC”) for a better understanding of the risks and uncertainties that investors in our securities should consider.

We may offer the securities directly to investors, through agents designated from time to time by them or us, or to or through underwriters or dealers on a continuous or delayed basis. If any agents, underwriters, or dealers are involved in the sale of any of the securities, their names, and any applicable purchase price, fee, commission or discount arrangement with, between or among them, will be set forth, or will be calculable from the information set forth, in an accompanying prospectus supplement. For more detailed information, see “Plan of Distribution” beginning on page 15 of this prospectus.

Neither the SEC nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

This prospectus may not be used to sell securities unless accompanied by a prospectus supplement.

The date of this prospectus is February 16, 2016.

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ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement that we filed with the SEC using a “shelf” registration process. Under this shelf process, we may, from time to time, sell any combination of the securities described in this prospectus in one or more offerings.

This prospectus provides you with a general description of the securities we may offer. Each time we sell securities, we will provide a prospectus supplement that will contain specific information about the terms of that offering. The prospectus supplement may also add, update or change information contained in this prospectus. You should read both this prospectus and any prospectus supplement together with additional information described under the heading below “Where You Can Find More Information.”

We have not authorized anyone to provide you any information other than that contained or incorporated by reference in this prospectus or any related prospectus supplement. We take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. You may obtain copies of the registration statement, or of any document which we have filed as an exhibit to the registration statement or to any other SEC filing, either from the SEC or from our corporate secretary as described below. We are not making an offer of these securities in any state where the offer is not permitted. You should not assume that the information in this prospectus or in the accompanying prospectus supplement is accurate as of any date other than the dates printed on the front of each document.

Unless otherwise indicated or otherwise required by the context in which the term occurs, all references in this prospectus or a supplement to “we,” “our,” “us,” “company” or similar terms refer to Unit Corporation together with its subsidiaries.

FORWARD-LOOKING STATEMENTS

This prospectus, any accompanying prospectus supplement and the documents incorporated by reference herein or therein may include “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933, as amended (the “Securities Act”), and Section 21E of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). All statements, other than statements of historical facts, included or incorporated by reference in this prospectus, which address activities, events or developments which we expect or anticipate will or may occur in the future are forward-looking statements. The words “believes,” “intends,” “expects,” “anticipates,” “projects,” “estimates,” “predicts” and similar expressions are also intended to identify forward-looking statements.

These forward-looking statements are based on assumptions which we believe are reasonable based on current expectations and projections about future events and industry conditions and trends affecting our business. However, whether actual results and developments will conform to our expectations and predictions is subject to a number of risks and uncertainties that, among other things, could cause actual results to differ materially from those contained in the forward-looking statements, including without limitation the following:

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These statements are based on certain assumptions and analyses made by us in light of our experience and our perception of historical trends, current conditions and expected future developments as well as other factors we believe are appropriate in the circumstances. However, whether actual results and developments will conform to our expectations and predictions is subject to a number of risks and uncertainties which could cause actual results to differ materially from our expectations, including:

We describe these risks and uncertainties in greater detail under the caption “Risk Factors” in our most recent Form 10-K, as updated by any subsequent Quarterly Reports on Form 10-Q or Current Reports on Form 8-K that we have filed or will file with the SEC. You should read all other information contained or incorporated by reference into this prospectus and the risk factors and other information contained in the applicable prospectus supplement before deciding to invest in our securities. See “Where You Can Find More Information” and “Documents Incorporated by Reference.”

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You should not place undue reliance on any of these forward-looking statements. We disclaim any current intention to update forward-looking information and to release publicly the results of any future revisions we may make to forward-looking statements to reflect events or circumstances after the date of this prospectus or the accompanying prospectus supplement to reflect the occurrence of unanticipated events.

WHO WE ARE

We were founded in 1963 as an oil and natural gas contract drilling company. Today, in addition to our drilling operations, we have operations in the exploration and production and mid-stream areas. We operate, manage, and analyze our results of operations through our three principal business segments:

Our operations are mainly located in the Mid-Continent, Rocky Mountain, and Gulf Coast regions with additional activity in the Permian and Appalachian Basins. Our principal executive offices are located at 7130 South Lewis, Suite 1000, Tulsa, Oklahoma 74136, and our telephone number is (918) 493-7700. Our common stock trades on the New York Stock Exchange under the symbol “UNT.”

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USE OF PROCEEDS

Except as otherwise described in any prospectus supplement, the net proceeds from the sale of securities offered from time to time will be used for general corporate purposes, which may include:

THE SECURITIES WE MAY OFFER

This prospectus is part of a shelf registration statement. Under this shelf registration statement, we may offer and sell from time to time any of the following securities:

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DESCRIPTION OF DEBT SECURITIES

The following description of the terms of the debt securities, which may consist of senior notes and debentures and subordinated notes and debentures, describes certain general terms and provisions of the debt securities to which any prospectus supplement may relate. The particular terms of the debt securities offered by any prospectus supplement and the extent, if any, to which the general provisions may apply to the debt securities being offered will be described in the prospectus supplement relating to the debt securities. You will need to review both the prospectus supplement and the following description for a description of the terms of a particular issue of our debt securities.

The debt securities will be general obligations and may be subordinated to our senior indebtedness (as discussed below) to the extent described in the applicable prospectus supplement. See “Description of Debt Securities—Subordination” below. Debt securities will be issued under an indenture to be entered into between us and an indenture trustee to be selected by us and named in a prospectus supplement. A copy of the form of indenture has been filed as an exhibit to the registration statement. This discussion of certain provisions of the indenture is a summary only and is not a complete description of the terms and provisions of the indenture. This discussion is completely qualified by reference to the actual terms of the indenture. Whenever defined terms are used but not defined in this prospectus, those terms have the meanings specified in the indenture.

General

The indenture does not limit the aggregate principal amount of debt securities that we may issue. We may issue the debt securities from time to time in one or more series. The indenture does not limit the amount of other unsecured indebtedness or securities which we may issue. Unless otherwise indicated in the applicable prospectus supplement, the debt securities will not benefit from any covenant or other provision that would give holders of debt securities special protection in the event of a highly leveraged transaction involving us. The applicable prospectus supplement will contain the following terms of the debt securities of the series for which the prospectus supplement is being delivered:

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Senior debt securities may be issued as original issue discount senior debt securities, which bear no interest or interest at a rate which at the time of issuance is below market rates, to be sold at a substantial discount below their stated principal amount due at the stated maturity of the senior debt securities. There may not be periodic payments of interest on original issue discount securities. In the event of an acceleration of the maturity of any original issue discount security, the amount payable to the holder of the original issue discount security on acceleration will be determined in accordance with the prospectus supplement, the terms of the security and the indenture, but will be an amount less than the amount payable at the maturity of the principal of the original issue discount security.

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If the senior debt securities are issued with “original issue discount” within the meaning of the Internal Revenue Code of 1986, as amended, then a holder of those senior debt securities will be required under the Internal Revenue Code to include original issue discount in ordinary income for federal income tax purposes as it accrues, in accordance with a constant interest method that takes into account the compounding of interest, in advance of receipt of cash attributable to that income. Generally, the total amount of original issue discount on a senior debt security will be the excess of the stated redemption price at maturity of the security over the price at which the security is sold to the public. To the extent a holder of a senior debt security receives a payment (at the time of acceleration of maturity, for example) that represents payment of original issue discount already included by the holder in ordinary income or reflected in the holder’s tax basis in the security, that holder generally will not be required to include the payment in income. The specific terms of any senior debt securities that are issued with original issue discount and the application of the original discount rules under the Internal Revenue Code to those securities will be described in a prospectus supplement for those securities.

Payments of interest on debt securities will be made at the corporate trust office of the trustee or at our option by check mailed to the registered holders of debt securities or, if so provided in the applicable prospectus supplement, at the option of a holder by wire transfer to an account designated by the holder.

Unless otherwise provided in the applicable prospectus supplement, debt securities may be transferred or exchanged at the office of the trustee at which its corporate trust business is principally administered in the United States, subject to the limitations provided in the indenture, without the payment of any service charge, other than any applicable tax or governmental charge.

Global Securities

The debt securities of a series may be issued in whole or in part in the form of one or more fully registered global securities that will be deposited with a depositary or its nominee identified in the prospectus supplement relating to the series. In that case, one or more global securities will be issued in a denomination or aggregate denominations equal to the portion of the aggregate principal amount of outstanding registered debt securities of the series to be represented by the global security or securities. Until it is exchanged in whole or in part for debt securities in definitive registered form, a global security may not be transferred except as a whole by the depositary for the global security to a nominee of the depositary or by a nominee of the depositary to the depositary or another nominee of the depositary or by the depositary or any nominee to a successor of the depositary or a nominee of the successor.

The specific terms of any depositary arrangement will be described in the prospectus supplement relating to the series. We anticipate that the following provisions will apply to all depositary arrangements.

If we issue a global security, the depositary for the global security will credit on its system, the respective principal amounts of the debt securities represented by the global security to the accounts of persons that have accounts with the depositary (“participants”). The underwriters or agents participating in the distribution of the debt securities will designate the amounts to be credited. Ownership of beneficial interests in a global security will be limited to participants or persons that may hold interests through participants. Ownership and transfer of beneficial interests in the global security will be effected only through records maintained by the depositary for the global security (with respect to interests of participants) or by participants or persons that hold through participants (with respect to interests of persons other than participants). While the depositary for a global security, or its nominee, is the registered owner of the global security, the depositary or the nominee, as the case may be, will be the sole owner or holder of the debt securities represented by the global security for all purposes under the indenture. Except as described below, owners of a beneficial interest in a global security will not be entitled to have the debt securities represented by the global security registered in their names, will not receive or be entitled to receive physical delivery of the debt securities and will not be considered the owners or holders of the debt securities under the indenture.

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Principal, premium, if any, and interest payments on debt securities represented by a global security registered in the name of a depositary or its nominee will be made to the depositary or its nominee, as the case may be, as the registered owner of the global security. We, the trustee or any paying agent for the debt securities will not have any responsibility or liability for the records relating to or payments made on account of beneficial ownership interests in the global securities or for maintaining, supervising or reviewing any records relating to those beneficial ownership interests.

We expect that the depositary for any debt securities represented by a global security, on receipt of any payment of principal, premium, or interest, will immediately credit participants’ accounts with payments in amounts proportionate to their respective beneficial interests in the principal amount of the global security as shown on the records of the depositary. We also expect that payments by participants to owners of beneficial interests in the global security held through the participants will be governed by standing instructions and customary practices, as is now the case with the securities held for the accounts of customers registered in “street name,” and will be the responsibility of the participants.

If the depositary for any debt securities represented by a global security is at any time unwilling or unable to continue as depositary and a successor depositary is not appointed by us within 90 days, we will issue the debt securities in exchange for the global security. Also, we may determine not to have any of the debt securities of a series represented by one or more global securities. In that event, we will issue debt securities of that series in definitive form in exchange for the global security or securities representing the debt securities.

Subordination

Debt securities may be subordinated to the prior payment of all our indebtedness that is designated as “senior indebtedness.” Senior indebtedness, with respect to any series of subordinated debt securities, will consist of any of our indebtedness that is designated in a resolution of our board of directors or the supplemental indenture establishing the series as senior indebtedness with respect to the series.

If we make a payment or distribution of our assets to our creditors or if there is a total or partial liquidation or we are dissolved or we file for bankruptcy, receivership, or similar proceeding, the holders of the senior indebtedness will be paid in full before the holders of the subordinated debt would receive any payment with respect to the subordinated debt securities. Until the senior indebtedness is paid in full, there will be no distribution to the holders of the subordinated debt securities (except that the holders may receive shares of stock and any debt securities that are subordinated to senior indebtedness to at least the same extent as the subordinated debt securities).

We may not make any payments of principal, premium, or interest with respect to subordinated debt securities, make any deposit for the purpose of defeasance of the subordinated debt securities, or repurchase, redeem, or otherwise retire (except, in the case of subordinated debt securities that provide for a mandatory sinking fund, by the delivery of subordinated debt securities by us to the trustee in satisfaction of our sinking fund obligation) any subordinated debt securities if:

unless, in either case,

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During any default (other than a default described in clause (a) or (b) above) on any senior indebtedness under which the maturity of the senior indebtedness may be accelerated without further notice (except any notice required to effect the acceleration) or the expiration of any applicable grace periods, we may not pay the subordinated debt securities for a period (the “payment blockage period”) starting on our receipt and the trustee’s receipt of written notice of the election to effect a payment blockage period and ending after 179 days. The payment blockage period may be terminated before its expiration by written notice to the trustee and to us from the person who gave the blockage notice, by repayment in full in cash of the senior indebtedness with respect to which the blockage notice was given, or because the default giving rise to the payment blockage period is no longer continuing. Unless the holders of the senior indebtedness have accelerated the maturity of the senior indebtedness, we may resume payments on the subordinated debt securities after the expiration of the payment blockage period. Not more than one blockage notice may be given in any period of 360 consecutive days unless the first blockage notice within the 360-day period is given by or on behalf of holders of designated senior indebtedness other than the bank indebtedness, in which case the representative of the bank indebtedness may give another blockage notice within the period. In no event, however, may the total number of days during which any payment blockage period or periods is in effect exceed 179 days in the aggregate during any period of 360 consecutive days. After all senior indebtedness is paid in full and until the subordinated debt securities are paid in full, holders of the subordinated debt securities will be subrogated to the rights of holders of senior indebtedness to receive distributions applicable to senior indebtedness.

As a result of the subordination provisions, in the event of our bankruptcy or insolvency, our creditors who are holders of senior indebtedness, as well as certain of our general creditors, may recover ratably more than the holders of the subordinated debt securities.

Subsidiary Guarantees

If specified in a prospectus supplement, one or more of our subsidiaries may guarantee our obligations relating to our debt securities issued under this prospectus. The specific terms and provisions of each subsidiary guarantee, including any provisions relating to the subordination of any subsidiary guarantee, will be described in the applicable prospectus supplement. The obligations of each subsidiary guarantor under its subsidiary guarantee will be limited as necessary to seek to prevent that subsidiary guarantee from constituting a fraudulent conveyance or fraudulent transfer under applicable federal or state law.

Events of Default and Remedies

The following events are defined in the indenture as “events of default” with respect to a series of debt securities:

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and the order or decree continues unstayed and in effect for 60 consecutive days, or any similar relief is granted under any foreign laws and the order or decree stays in effect for 60 consecutive days; or

An event of default with respect to one series of debt securities is not necessarily an event of default for another series.

If an event of default occurs and is continuing with respect to any series of debt securities, unless the principal and interest with respect to all the debt securities of the series have already become due and payable, either the trustee or the holders of not less than 25% in aggregate principal amount of the debt securities of the series then outstanding may declare the principal of (or, if original issue discount debt securities, the portion of the principal amount as may be specified in the series) and interest on all the debt securities of the series due and payable immediately.

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If an event of default occurs and is continuing, the trustee will be entitled to institute any action or proceeding for the collection of the sums due and unpaid or to enforce the performance of any provision of the debt securities of the affected series or the indenture, to prosecute the action or proceeding to judgment or final decree, and to enforce any judgment or final decree against us or any other obligor on the debt securities of the series. In addition, if there is pending proceedings for the bankruptcy or reorganization of the company or any other obligor on the debt securities, or if a receiver, trustee, or similar official is appointed for our property, the trustee will be entitled to file and prove a claim for the whole amount of principal, premium and interest (or, in the case of original issue discount debt securities, the portion of the principal amount as may be specified in the terms of the series) owing and unpaid with respect to the debt securities. No holder of any debt securities of any series will have any right to institute any action or proceeding with respect to the indenture, for the appointment of a receiver or trustee, or for any other remedy, unless:

Before the acceleration of the maturity of the debt securities of any series, the holders of a majority in aggregate principal amount of the debt securities of that series at the time outstanding may, on behalf of the holders of all debt securities of that series, waive any past default or event of default and its consequences for that series, except:

In the case of a waiver, the default will cease to exist, any event of default arising from the default will be deemed to have been cured for all purposes, and we, the trustee and the holders of the debt securities of that series will each be restored to their former positions and rights under the indenture.

The trustee will, within 90 days after the occurrence of a default known to it with respect to a series of debt securities, give to the holders of the debt securities notice of all uncured defaults known to it, unless the defaults have been cured or waived before giving the notice; provided, however, that except in the case of default in the payment of principal, premium, or interest with respect to the debt securities or in the making of any sinking fund payment with respect to the debt securities, the trustee will be protected in withholding the notice if it in good faith determines that withholding the notice is in the interest of the holders of the debt securities.

Modification of the Indenture

We and the trustee may enter into supplemental indentures without the consent of the holders of debt securities issued under the indenture for one or more of the following purposes:

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With the consent of the holders of a majority in aggregate principal amount of the outstanding debt securities of each series affected, we and the trustee may from time to time and at any time enter into a supplemental indenture for the purpose of adding any provisions to, changing in any manner, or eliminating any of the provisions of the indenture or of any supplemental indenture or modifying in any manner the rights of the holder of the debt securities of the series. However, without the consent of the holders of each debt security that is affected, the supplemental indenture may not:

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Consolidation, Merger, and Sale of Assets

The indenture provides that we may not consolidate with or merge with or into any person, or convey, transfer, or lease all or substantially all of our assets, unless the following conditions have been satisfied:

Satisfaction and Discharge of the Indenture

The indenture provides, among other things, that when all debt securities not previously delivered to the trustee for cancellation (1) have become due and payable or (2) will become due and payable at their stated maturity within one year, we may deposit with the trustee funds, in trust, for the purpose and in an amount sufficient to pay and discharge the entire indebtedness on the debt securities not previously delivered to the trustee for cancellation. Those funds will include all principal, premium, if any, and interest, if any, to the date of the deposit or to the stated maturity, as applicable. At the time of the deposit, the indenture will cease to be of further effect, except as to our obligations to pay all other sums due under the indenture and to provide the officers’ certificates and opinions of counsel required under the indenture. At that time we will be deemed to have satisfied and discharged the indenture.

Governing Law

The indenture and the debt securities will be governed by, and construed in accordance with, the laws of the State of New York.

Regarding the Trustee

Information concerning the trustee for a series of debt securities will be described in the prospectus supplement relating to that series of debt securities.

We may have normal banking relationships with the trustee in the ordinary course of business.

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DESCRIPTION OF CAPITAL STOCK

We have 180,000,000 authorized shares of capital stock, consisting of (a) 175,000,000 shares of common stock, having a par value of $0.20 per share, and (b) 5,000,000 shares of preferred stock, having a par value of $1.00 per share. As of February 12, 2016, there were 51,023,390 shares of our common stock outstanding. No preferred stock is outstanding.

Common Stock

All of the outstanding shares of common stock are fully paid and nonassessable.

Our stockholders are entitled to receive dividends, when, as and if declared by our board of directors out of assets legally available for their payment. In certain cases, we may not pay dividends to common stockholders until our dividend obligations to the holder of any preferred stock then outstanding have been satisfied. The provisions of our credit arrangements subject us to certain restrictions on the payment of dividends.

In the event of our voluntary or involuntary liquidation, dissolution or winding up, our stockholders will be entitled to share equally in our assets remaining after payment of all liabilities and after holders of all series of outstanding preferred stock have received their liquidation preferences in full.

Our stockholders have no preemptive, subscription, conversion or redemption rights, and are not subject to further calls or assessments by us. There are no sinking fund provisions applicable to the common stock.

Our stockholders are entitled to one vote per share for the election of directors and on all other matters submitted to a vote of stockholders. Holders of common stock have no right to cumulate their votes in the election of directors.

Preferred Stock

As of the date of this prospectus, there were no shares of preferred stock outstanding.

Preferred stock may be issued from time to time in one or more series, and our board of directors, without further approval of the stockholders, is authorized to fix the dividend rates and terms, conversion rights, voting rights, redemption rights and terms, liquidation preferences, sinking fund and any other rights, preferences, privileges and restrictions applicable to each series of preferred stock. The purpose of authorizing the board of directors to determine these rights, preferences, privileges and restrictions is to eliminate delays associated with a stockholder vote on specific issuances. The issuance of preferred stock, while providing flexibility in connection with possible acquisitions and other corporate purposes, could, among other things, decrease the amount of earnings and assets available for distribution to holders of common stock, adversely affect the rights and powers, including voting rights, of holders of common stock and have the effect of delaying, deferring or preventing a change in control of us.

Certain Possible Anti-takeover Provisions

Our by-laws, charter and Delaware law contain certain provisions that might be characterized as anti-takeover provisions. These provisions may make it more difficult to acquire control of us or remove our management.

Classified Board of Directors

Our by-laws provide for our board of directors to be divided into three classes of directors serving staggered three-year terms, with the number of directors in each class to be as nearly equal as possible. As a result, and assuming all classes have the same number of directors, only one-third of our directors are elected each year.

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Issuance of Preferred Stock

As described above, our charter authorizes a class of undesignated preferred stock consisting of 5,000,000 shares. The issuance of preferred stock could, among other things, make it more difficult for a third party to gain control of us.

Fair Price Provisions

Our charter also contains certain “fair price provisions” designated to provide safeguards for stockholders when an “interested stockholder” (defined as a stockholder owning 5% or more of our voting stock) attempts to effect a “business combination” with us. The term “business combination” includes:

In general, a business combination between us and the interested stockholder must be approved by the affirmative vote of 80% of the outstanding voting stock unless the transaction is approved by a majority of the members of the Board of Directors who are not affiliated with the interested stockholder or certain minimum price and form of consideration requirements are satisfied.

Delaware Business Combination Statute

We are incorporated under the laws of the State of Delaware. Section 203 of the Delaware General Corporation Law prevents an “interested stockholder” (defined as a stockholder owning 15% or more of a corporation’s voting stock) from engaging in a business combination with that corporation for a period of three years from the date the stockholder became an interested stockholder unless:

Since we have not amended our charter or by-laws to exclude the application of Section 203, its provisions apply to us. Accordingly, Section 203 may inhibit an interested stockholder’s ability to acquire additional shares of common stock or otherwise engage in a business combination with us.

Special Meetings of Stockholders

Our bylaws provide that special meetings of the stockholders may be called at any time only by the board of directors or the president.

Advance Notice for Raising Business or Making Nominations at Meetings

Our by-laws establish an advance notice procedure for stockholder proposals to be brought before an annual meeting of stockholders and for nominations by stockholders of candidates for election as directors at an annual or special meeting at which directors are to elected.

The only business that may be conducted at an annual meeting of stockholders is that which has been brought before the meeting by, or at the direction of, the board of directors or by a stockholder who has given to

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our secretary timely written notice, in proper form, of the stockholder’s intention to bring that business before the meeting. Only persons who are nominated by, or at the direction of, the board of directors, or who are nominated by a stockholder who has given timely written notice, in proper form, to the secretary before a meeting at which directors are to be elected will be eligible for election as directors. The person presiding at the meeting will have the authority to make determinations whether a stockholder’s notice complies with the procedures in our by-laws.

To be timely, notice of business to be brought before an annual meeting or nominations of candidates for election as directors at an annual meeting is generally required to be received by our secretary not later than 90 days nor earlier than 120 days before the first anniversary of the prior year’s annual meeting date.

The notice of any nomination for election as a director is required to describe the information regarding that person required in our by-laws as well as by paragraphs (a), (e), and (f) of Item 401 of regulation S-K adopted by the SEC.

Transfer Agent and Registrar

The Transfer Agent and Registrar for our common stock is American Stock Transfer & Trust Company, LLC.

DESCRIPTION OF WARRANTS

General

We may issue warrants to purchase debt securities or, warrants to purchase common stock or preferred stock. Warrants may be issued independently of or together with any other securities and may be attached to or separate from those securities. Each series of warrants will be issued under a separate warrant agreement to be entered into between us and a warrant agent. The warrant agent will act solely as our agent in connection with any warrant and will not assume any obligation or relationship of agency for or with holders or beneficial owners of warrants. The following summaries describe certain general terms and provisions of the warrants. Further terms of the warrants and the applicable warrant agreement will be described in the applicable prospectus supplement.

Debt Warrants

The applicable prospectus supplement will describe the terms of any debt warrants, including the following:

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Stock Warrants

The applicable prospectus supplement will describe the terms of any stock warrants, including the following:

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DESCRIPTION OF PURCHASE CONTRACTS

We may issue purchase contracts, including contracts obligating holders to purchase from us and us to sell to the holders, a specified principal amount of debt securities or a specified number of shares of common stock or preferred stock or any of the other securities that we may sell under this prospectus (or a range of principal amount or number of shares under a predetermined formula) at a future date or dates. The consideration payable on settlement of the purchase contracts may be fixed at the time the purchase contracts are issued or may be determined by a specific reference to a formula described in the purchase contracts. The purchase contracts may be issued separately or as part of units consisting of a purchase contract and other securities or obligations issued by us or third parties, including United States treasury securities, securing the holders’ obligations to purchase the relevant securities under the purchase contracts.

The purchase contracts may require us to make periodic payments to the holders of the purchase contracts or units or vice versa, and the payments may be unsecured or prefunded on some basis. The purchase contracts may require holders to secure their obligations under the purchase contracts in a specified manner and in some circumstances we may deliver newly issued prepaid purchase contracts, often referred to as “prepaid securities,” on release to a holder of any collateral securing the holder’s obligations under the original purchase contract.

The applicable prospectus supplement will describe the terms of any purchase contracts or purchase units and, if applicable, other securities or obligations. The description in the prospectus supplement will not necessarily be complete and will be qualified in its entirety by reference to the purchase contracts, and, if applicable, collateral arrangements, relating to the purchase contracts.

DESCRIPTION OF UNITS

We may issue units consisting of one or more purchase contracts, warrants, debt securities, shares of preferred stock, shares of common stock or any combination of those securities. The applicable prospectus supplement will describe:

PLAN OF DISTRIBUTION

We may sell offered securities in any one or more of the following ways from time to time:

Any underwriter, dealer or agent may be deemed to be an “underwriter” within the meaning of the Securities Act.

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The prospectus supplement with respect to the offered securities will describe the terms of the offering, including:

Any initial public offering price, discounts or concessions allowed or reallowed or paid to dealers may be changed from time to time.

The distribution of the offered securities may be effected from time to time in one or more transactions:

Offers to purchase offered securities may be solicited by agents designated by us from time to time. Any agent involved in the offer or sale of the offered securities will be named, and any commissions payable by us to the agent will be described in the applicable prospectus supplement. Unless otherwise indicated in the prospectus supplement, the agent will be acting on a reasonable best efforts basis for the period of its appointment.

If offered securities are sold by means of an underwritten offering, we will execute an underwriting agreement with an underwriter or underwriters, and the names of the specific managing underwriter or underwriters, as well as any other underwriters, and the terms of the transaction, including commissions, discounts and any other compensation of the underwriters and dealers, if any, will be described in the prospectus supplement which will be used by the underwriters to make resales of the offered securities. If underwriters are utilized in the sale of the offered securities, the offered securities will be acquired by the underwriters for their own account and may be resold from time to time in one or more transactions, including negotiated transactions, at fixed public offering prices or at varying prices determined by the underwriters at the time of sale. Our offered securities may be offered to the public either through underwriting syndicates represented by managing underwriters or directly by the managing underwriters. If any underwriter or underwriters are utilized in the sale of the offered securities, unless otherwise indicated in the prospectus supplement, the underwriting agreement will provide that the obligations of the underwriters are subject to certain conditions precedent and that the underwriters with respect to a sale of offered securities will be obligated to purchase all offered securities of a series if any are purchased.

We may grant to the underwriters options to purchase additional offered securities, to cover over-allotments, if any, at the public offering price, with additional underwriting discounts or commissions, as may be described in the prospectus supplement relating thereto. If we grant any over-allotment option, the terms of the over-allotment option will be described in the prospectus supplement relating to the offered securities.

If a dealer is utilized in the sales of offered securities we will sell the offered securities to the dealer as principal. The dealer may then resell the offered securities to the public at varying prices to be determined by the

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dealer at the time of resale. The dealer may be deemed to be an underwriter, as the term is defined in the Securities Act, of the offered securities so offered and sold. The name of the dealer and the terms of the transaction will be described in the related prospectus supplement.

Offers to purchase offered securities may be solicited directly by us and the sale may be made by us directly to institutional investors or others, who may be deemed to be underwriters within the meaning of the Securities Act with respect to any resale of the securities. The terms of the sales will be described in the related prospectus supplement.

Offered securities may also be offered and sold, if so indicated in the applicable prospectus supplement, in connection with a remarketing on their purchase, in accordance with a redemption or repayment under their terms, or otherwise, by one or more firms acting as principals of their own accounts or as agents for us. Any remarketing firm will be identified and the terms of its agreements, if any, with us and its compensation will be described in the applicable prospectus supplement. Remarketing firms may be deemed to be underwriters, as that term is defined in the Securities Act, in connection with the offered securities remarketed thereby.

Agents, underwriters, dealers and remarketing firms may be entitled under relevant agreements entered into with us to indemnification by us against certain civil liabilities, including liabilities under the Securities Act that may arise from any untrue statement or alleged untrue statement of a material fact or any omission or alleged omission to state a material fact in this prospectus, any supplement or amendment hereto, or in the registration statement of which this prospectus forms a part, or to contribution with respect to payments which the agents, underwriters or dealers may be required to make.

Each class or series of securities will be a new issue of securities with no established trading market, other than our common stock, which is listed on the New York Stock Exchange. We may elect to list any other class or series of securities on any exchange, but are not obligated to do so. Any underwriters to whom securities are sold by us for public offering and sale may make a market in the securities, but the underwriters will not be obligated to do so and may discontinue any market making at any time without notice. No assurance can be given as to the liquidity of the trading market for any securities.

LEGAL MATTERS

The validity of the offered securities will be passed upon for us by Conner & Winters, LLP, Tulsa, Oklahoma. Certain other legal matters will be passed upon for us by Conner & Winters, LLP, Tulsa, Oklahoma, and for the underwriters, dealers or agents, if any, by their own legal counsel. As of the date of this prospectus, attorneys at Conner & Winters, LLP owned 4,770 shares of our common stock.

EXPERTS

The financial statements and management’s assessment of the effectiveness of internal control over financial reporting (which is included in Management’s Report on Internal Controls over Financial Reporting) incorporated in this prospectus by reference to the Annual Report on Form 10-K for the fiscal year ended December 31, 2014 have been incorporated in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of the firm as experts in auditing and accounting.

We have derived the estimates of proved oil and natural gas reserves and related future net revenues and their present value as of December 31, 2014 included in our Annual Report on Form 10-K for the year ended December 31, 2014 and incorporated by reference in this prospectus from the reserves audit report of Ryder Scott Company, L.P., independent petroleum engineers, given on the authority of Ryder Scott Company, L.P. as experts in those matters.

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WHERE YOU CAN FIND MORE INFORMATION

We file annual, quarterly and current reports, proxy statements and other information and documents with the SEC. You may read and copy any document we file with the SEC at:

This prospectus is one part of a registration statement filed on Form S-3 (together with all amendments, supplements, schedules and exhibits to the registration statement, referred to as the registration statement) with the SEC under the Securities Act. This prospectus does not contain all of the information described in the registration statement and the exhibits and schedules to the registration statement. For further information concerning us and the securities, you should read the entire registration statement and the additional information described under “Documents Incorporated By Reference” below. The registration statement has been filed electronically and may be obtained in any manner listed above. Any statements contained herein concerning the provisions of any document are not necessarily complete, and, in each instance, reference is made to the copy of the document filed as an exhibit to the registration statement or otherwise filed with the SEC. Each statement is qualified in its entirety by the documents incorporated by reference.

DOCUMENTS INCORPORATED BY REFERENCE

The SEC allows us to “incorporate by reference” into this prospectus the information we file with them, which means we can disclose important business and financial information about us to you by referring you to those documents. The information incorporated by reference is considered to be a part of this prospectus, except for any information that is superseded by information included directly in this prospectus and any prospectus supplement. Information that we file later with the SEC will also automatically update and supersede the information in this prospectus. We incorporate by reference the documents listed below that we previously filed with the SEC and any future filings we make with the SEC under Section 13(a), 13(c), 14 or 15(d) of the Exchange Act (other than any portions of the filings that are furnished rather than filed under applicable SEC rules) until the termination of the offering made under this prospectus:

We will provide at no cost to each holder, including any beneficial owner of the offered securities, to whom this prospectus or any supplement is delivered, a copy of the reports and any or all of the information that has been incorporated by reference but not delivered with this prospectus or any supplement. Please direct your oral or written request to Mark E. Schell, Senior Vice President, Secretary and General Counsel, at our principal executive offices located at:

7130 South Lewis

Suite 1000

Tulsa, Oklahoma 74136

(918) 493-7700

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ITEM 15. INDEMNIFICATION OF DIRECTORS AND OFFICERS.

Article 4 of our by-laws provides for indemnification of any person who is, or is threatened to be made a party to, or is otherwise involved in, any proceeding by reason of his or her position as a director or officer against expenses and liabilities incurred by them in connection with any suit to which they are, or are threatened to be made, a party by reason of their serving in their positions so long as they acted in good faith and in a manner they reasonably believe to be in, or not opposed to, the best interests of the corporation, and with respect to any criminal action, they had no reasonable cause to believe their conduct was unlawful. With respect to suits by or in the right of a corporation, however, indemnification is generally limited to attorney’s fees and other expenses and is not available if the person is adjudged to be liable to the corporation unless the court determines that indemnification is appropriate. In addition, a corporation has the power to purchase and maintain insurance for these persons. Article 4 of our by-laws also expressly provides that the power to indemnify authorized thereby is not exclusive of any other rights to which any present and former directors and officers may be entitled.

Article 9 of our charter eliminates in certain circumstances the monetary liability of our directors for a breach of their fiduciary duty as directors. These provisions do not eliminate the liability of a director

We have purchased directors and officer’s liability insurance that would indemnify our directors and officers against damages arising out of certain kinds of claims that might be made against them based on their negligent acts or omissions while performing their duties.

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Our policy is to enter into separate indemnification agreements with each of our directors and executive officers that provide the maximum indemnity allowed to directors and executive officers by Section 145 of the Delaware General Corporation Law and which allow for certain additional procedural protections.

The above discussion of our charter, by-laws, indemnification agreements and of Section 145 of the Delaware General Corporation Law is not exhaustive and is qualified in its entirety by our charter, our by-laws, the indemnification agreements and statute.

ITEM 17. UNDERTAKINGS.

provided, however, that paragraphs (a)(1)(i), (a)(1)(ii) and (a)(1)(iii) do not apply if the information required to be included in a post-effective amendment by those paragraphs is contained in reports filed with or furnished to the SEC by the registrant under Section 13 or Section 15(d) of the Exchange Act that are incorporated by reference in the registration statement, or is contained in a form of prospectus filed under Rule 424(b) that is part of the registration statement.

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SIGNATURES

Pursuant to the requirements of the Securities Act, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Tulsa, State of Oklahoma, on February 16, 2016.

Pursuant to the requirements of the Securities Act, this registration statement has been signed by the following persons in the capacities indicated on February 16, 2016.

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*By: /s/ Mark E. Schell

Mark E. Schell, Attorney-in-fact

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SIGNATURES

Pursuant to the requirements of the Securities Act, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Tulsa, State of Oklahoma, on February 16, 2016.

Pursuant to the requirements of the Securities Act, this registration statement has been signed by the following persons in the capacities indicated on February 16, 2016.

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SIGNATURES

Pursuant to the requirements of the Securities Act, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Tulsa, State of Oklahoma, on February 16, 2016.

Pursuant to the requirements of the Securities Act, this registration statement has been signed by the following persons in the capacities indicated on February 16, 2016.

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SIGNATURES

Pursuant to the requirements of the Securities Act, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Tulsa, State of Oklahoma, on February 16, 2016.

Pursuant to the requirements of the Securities Act, this registration statement has been signed by the following persons in the capacities indicated on February 16, 2016.

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SIGNATURES

Pursuant to the requirements of the Securities Act, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Tulsa, State of Oklahoma, on February 16, 2016.

Pursuant to the requirements of the Securities Act, this registration statement has been signed by the following persons in the capacities indicated on February 16, 2016.

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SIGNATURES

Pursuant to the requirements of the Securities Act, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Tulsa, State of Oklahoma, on February 16, 2016.

Pursuant to the requirements of the Securities Act, this registration statement has been signed by the following persons in the capacities indicated on February 16, 2016.

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SIGNATURES

Pursuant to the requirements of the Securities Act, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Tulsa, State of Oklahoma, on February 16, 2016.

Pursuant to the requirements of the Securities Act, this registration statement has been signed by the following persons in the capacities indicated on February 16, 2016.

*By: /s/ Mark E. Schell

Mark E. Schell, Attorney-in-fact

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SIGNATURES

Pursuant to the requirements of the Securities Act, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Tulsa, State of Oklahoma, on February 16, 2016.

Pursuant to the requirements of the Securities Act, this registration statement has been signed by the following persons in the capacities indicated on February 16, 2016.

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SIGNATURES

Pursuant to the requirements of the Securities Act, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Tulsa, State of Oklahoma, on February 16, 2016.

Pursuant to the requirements of the Securities Act, this registration statement has been signed by the following persons in the capacities indicated on February 16, 2016.

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SIGNATURES

Pursuant to the requirements of the Securities Act, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Tulsa, State of Oklahoma, on February 16, 2016.

Pursuant to the requirements of the Securities Act, this registration statement has been signed by the following persons in the capacities indicated on February 16, 2016.

*By: /s/ Mark E. Schell

Mark E. Schell, Attorney-in-fact

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SIGNATURES

Pursuant to the requirements of the Securities Act, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Tulsa, State of Oklahoma, on February 16, 2016.

Pursuant to the requirements of the Securities Act, this registration statement has been signed by the following persons in the capacities indicated on February 16, 2016.

*By: /s/ Mark E. Schell

Mark E. Schell, Attorney-in-fact

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SIGNATURES

Pursuant to the requirements of the Securities Act, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Tulsa, State of Oklahoma, on February 16, 2016.

Pursuant to the requirements of the Securities Act, this registration statement has been signed by the following persons in the capacities indicated on February 16, 2016.

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