UNDERWRITING AGREEMENT

ANADARKO PETROLEUM CORPORATION

30,000,000 Shares

Common Stock

($0.10 par value per Share)

U NDERWRITING A GREEMENT

May 11, 2009

U NDERWRITING A GREEMENT

May 11, 2009

UBS Securities LLC

Barclays Capital Inc.

    as Managing Underwriters

c/o UBS Securities LLC

299 Park Avenue

New York, New York 10171-0026

Ladies and Gentlemen:

Anadarko Petroleum Corporation, a Delaware corporation (the “ Company ”), proposes to issue and sell to the underwriters named in Schedule A annexed hereto (the “ Underwriters ”), for whom you are acting as representatives, an aggregate of 30,000,000 shares (the “ Firm Shares ”) of common stock, $0.10 par value per share (the “ Common Stock ”), of the Company. In addition, solely for the purpose of covering over-allotments, the Company proposes to grant to the Underwriters the option to purchase from the Company up to an additional 4,500,000 shares of Common Stock (the “ Additional Shares ”). The Firm Shares and the Additional Shares are hereinafter collectively sometimes referred to as the “ Shares .” The Shares are described in the Prospectus which is referred to below.

The Company has prepared and filed, in accordance with the provisions of the Securities Act of 1933 and the rules and regulations thereunder (collectively, the “ Act ”), with the Securities and Exchange Commission (the “ Commission ”) a registration statement on Form S-3 (File No. 333-137183) under the Act (the “ registration statement ”), including a prospectus, which registration statement incorporates by reference documents which the Company has filed, or will file, in accordance with the provisions of the Securities Exchange Act of 1934 and the rules and regulations thereunder (collectively, the “ Exchange Act ”). Such registration statement has become effective under the Act.

Except where the context otherwise requires, “ Registration Statement ,” as used herein, means the registration statement, as amended at the time of such registration statement’s effectiveness for purposes of Section 11 of the Act, as such section applies to the respective Underwriters (the “ Effective Time ”), including (i) all documents filed as a part thereof or incorporated or deemed to be incorporated by reference therein, (ii) any information contained or incorporated by reference in a prospectus filed with the Commission pursuant to Rule 424(b) under the Act, to the extent such information is deemed, pursuant to Rule 430B or Rule 430C under the Act, to be part of the registration statement at the Effective Time, and (iii) any other registration statement filed to register the offer and sale of Shares pursuant to Rule 462(b) under the Act.

The Company has furnished to you, for use by the Underwriters and by dealers in connection with the offering of the Shares, copies of one or more preliminary prospectus supplements, and the documents incorporated by reference therein, relating to the Shares.

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Except where the context otherwise requires, “ Pre-Pricing Prospectus ,” as used herein, means each such preliminary prospectus supplement, in the form so furnished, including any basic prospectus (whether or not in preliminary form) furnished to you by the Company and attached to or used with such preliminary prospectus supplement. Except where the context otherwise requires, “ Basic Prospectus ,” as used herein, means any such basic prospectus and any basic prospectus furnished to you by the Company and attached to or used with the Prospectus Supplement (as defined below).

Except where the context otherwise requires, “ Prospectus Supplement ,” as used herein, means the final prospectus supplement, relating to the Shares, filed by the Company with the Commission pursuant to Rule 424(b) under the Act on or before the second business day after the date hereof (or such earlier time as may be required under the Act), in the form furnished by the Company to you for use by the Underwriters and by dealers in connection with the offering of the Shares.

Except where the context otherwise requires, “ Prospectus ,” as used herein, means the Prospectus Supplement together with the Basic Prospectus attached to or used with the Prospectus Supplement.

“ Permitted Free Writing Prospectuses ,” as used herein, means the documents listed on Schedule B attached hereto and each “road show” (as defined in Rule 433 under the Act), if any, related to the offering of the Shares contemplated hereby that is a “written communication” (as defined in Rule 405 under the Act). The Underwriters have not offered or sold and will not offer or sell, without the Company’s consent, any Shares by means of any “free writing prospectus” (as defined in Rule 405 under the Act) that is required to be filed by the Underwriters with the Commission pursuant to Rule 433 under the Act, other than a Permitted Free Writing Prospectus.

“ Covered Free Writing Prospectuses ,” as used herein, means (i) each “issuer free writing prospectus” (as defined in Rule 433(h)(1) under the Act) (“ Issuer Free Writing Prospectus ”), if any, relating to the Shares, which is not a Permitted Free Writing Prospectus and (ii) each Permitted Free Writing Prospectus.

“ Disclosure Package ,” as used herein, means any Pre-Pricing Prospectus or Basic Prospectus, in either case together with the pricing information orally conveyed with confirmations listed in Schedule C hereto and any combination of one or more of the Permitted Free Writing Prospectuses, if any.

“ Applicable Time ,” as used herein, means 8:30 A.M., New York City Time, on May 12, 2009.

Any reference herein to the registration statement, the Registration Statement, any Basic Prospectus, any Pre-Pricing Prospectus, the Prospectus Supplement, the Prospectus or any Permitted Free Writing Prospectus shall be deemed to refer to and include the documents, if any, incorporated by reference, or deemed to be incorporated by reference, therein (the “ Incorporated Documents ”), including, unless the context otherwise requires, the documents, if any, filed as

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exhibits to such Incorporated Documents. Any reference herein to the terms “ amend ,” “ amendment ” or “ supplement ” with respect to the Registration Statement, any Basic Prospectus, any Pre-Pricing Prospectus, the Prospectus Supplement, the Prospectus or any Permitted Free Writing Prospectus shall be deemed to refer to and include the filing of any document under the Exchange Act on or after the initial effective date of the Registration Statement, or the date of such Basic Prospectus, such Pre-Pricing Prospectus, the Prospectus Supplement, the Prospectus or such Permitted Free Writing Prospectus, as the case may be, and deemed to be incorporated therein by reference.

As used in this Agreement, “ business day ” shall mean a day on which the New York Stock Exchange (the “ NYSE ”) is open for trading. The terms “herein,” “hereof,” “hereto,” “hereinafter” and similar terms, as used in this Agreement, shall in each case refer to this Agreement as a whole and not to any particular section, paragraph, sentence or other subdivision of this Agreement. The term “or,” as used herein, is not exclusive.

The Company and the Underwriters agree as follows:

1. Sale and Purchase . Upon the basis of the representations and warranties and subject to the terms and conditions herein set forth, the Company agrees to issue and sell to the respective Underwriters and each of the Underwriters, severally and not jointly, agrees to purchase from the Company the number of Firm Shares set forth opposite the name of such Underwriter in Schedule A attached hereto, subject to adjustment in accordance with Section 10 hereof, in each case at a purchase price of $44.59 per Share. The Company is advised by you that the Underwriters intend (i) to make a public offering of their respective portions of the Firm Shares as soon after the effectiveness of this Agreement as in your judgment is advisable and (ii) initially to offer the Firm Shares upon the terms set forth in the Prospectus. You may from time to time increase or decrease the public offering price after the initial public offering to such extent as you may determine.

In addition, the Company hereby grants to the several Underwriters the option (the “ Over-Allotment Option ”) to purchase, and upon the basis of the representations and warranties and subject to the terms and conditions herein set forth, the Underwriters shall have the right to purchase, severally and not jointly, from the Company, ratably in accordance with the number of Firm Shares to be purchased by each of them, all or a portion of the Additional Shares as may be necessary to cover over-allotments made in connection with the offering of the Firm Shares, at the same purchase price per share to be paid by the Underwriters to the Company for the Firm Shares. The Over-Allotment Option may be exercised by UBS Securities LLC (“ UBS ”) and Barclays Capital Inc. (“ Barclays ”) on behalf of the several Underwriters at any time and from time to time on or before the thirtieth day following the date of the Prospectus Supplement, by written notice to the Company. Such notice shall set forth the aggregate number of Additional Shares as to which the Over-Allotment Option is being exercised and the date and time when the Additional Shares are to be delivered (any such date and time being herein referred to as an “ additional time of purchase ”); provided , however , that no additional time of purchase shall be earlier than the “time of purchase” (as defined below) nor earlier than the second business day after the date on which the Over-Allotment Option shall have been exercised nor later than the tenth business day after the date on which the Over-Allotment Option

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shall have been exercised. The number of Additional Shares to be sold to each Underwriter shall be the number which bears the same proportion to the aggregate number of Additional Shares being purchased as the number of Firm Shares set forth opposite the name of such Underwriter on Schedule A hereto bears to the total number of Firm Shares (subject, in each case, to such adjustment as UBS and Barclays may determine to eliminate fractional shares), subject to adjustment in accordance with Section 10 hereof.

2. Payment and Delivery . Payment of the purchase price for the Firm Shares shall be made to the Company by Federal Funds wire transfer against delivery of the Firm Shares through the facilities of The Depository Trust Company (“ DTC ”) for the respective accounts of the Underwriters. Such payment and delivery shall be made at 10:00 A.M., New York City time, on May 15, 2009 (unless another time shall be agreed to by you and the Company or unless postponed in accordance with the provisions hereof). The time at which such payment and delivery are to be made is hereinafter sometimes called the “ time of purchase .” Electronic transfer of the Firm Shares shall be made to you at the time of purchase in such names and in such denominations as you shall specify.

Payment of the purchase price for the Additional Shares shall be made at the additional time of purchase in the same manner and at the same office and time of day as the payment for the Firm Shares. Electronic transfer of the Additional Shares shall be made to you at the additional time of purchase in such names and in such denominations as you shall specify.

Deliveries of the documents with respect to the purchase of the Shares shall be made at the offices of Akin Gump Strauss Hauer & Feld LLP at 1111 Louisiana Street, Houston, Texas 77002, at 9:00 A.M., New York City time, on the date of the closing of the purchase of the Firm Shares or the Additional Shares, as the case may be.

3. Representations and Warranties of the Company . The Company represents and warrants to and agrees with each of the Underwriters that:

(a) The Company has filed with the Commission the Registration Statement, including the Basic Prospectus, covering the registration of the Shares under the Act, which has become effective.

(b) The Registration Statement constitutes an “ automatic shelf registration statement ” (as defined in Rule 405 of the Act) filed within three years of the date of this Agreement, and the Company is a “ well-known seasoned issuer ” (as defined in Rule 405 of the Act). The Company has not received from the Commission any notice pursuant to Rule 401(g)(2) objecting to use of the automatic shelf registration statement form. If at any time when any Shares remain unsold by the Underwriters the Company receives from the Commission a notice pursuant to Rule 401(g)(2) or otherwise ceases to be eligible to use the automatic shelf registration statement form, the Company will (i) promptly notify you, (ii) promptly file a new registration statement or post-effective amendment on the proper form relating to the Shares, in a form reasonably satisfactory to you, (iii) use its reasonable best efforts to cause such registration statement or post-effective amendment to be declared effective as soon as practicable, and (iv) promptly notify you of such effectiveness. The

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Company will take all other action reasonably necessary or appropriate to permit the public offering and sale of the Shares to continue as contemplated in the registration statement that was the subject of the Rule 401(g)(2) notice or for which the Company has otherwise become ineligible. References herein to the Registration Statement shall include such new registration statement or post-effective amendment, as the case may be. The Company has paid or shall pay the required Commission filing fees relating to the Shares within the time required by Rule 456(b)(1) without regard to the proviso therein and otherwise in accordance with Rules 456(b) and 457(r).

(c) (i) At the time of the filing of the Registration Statement and (ii) at the date of this Agreement, the Company was not and is not an “ineligible issuer,” as defined in Rule 405 under the Act.

(d) (i) (A) At the time the Registration Statement initially became effective, (B) at the time of each amendment thereto for the purposes of complying with Section 10(a)(3) of the Act (whether by post-effective amendment, incorporated report or form of prospectus), (C) on the Effective Date relating to the Shares and (D) at the time of purchase and any additional time of purchase, the Registration Statement conformed and will conform in all material respects to the requirements of the Act and did not and will not include any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary to make the statements therein not misleading and (ii) (A) on its date, (B) at the time of filing the Prospectus Supplement pursuant to Rule 424(b) and (C) at the time of purchase and any additional time of purchase, the Prospectus will conform in all material respects to the requirements of the Act and will not include any untrue statement of a material fact or omit to state any material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading. The preceding sentence does not apply to statements in or omissions from any such document made in reliance upon and in conformity with written information furnished to the Company by any Underwriter through you, if any, specifically for use therein, it being understood and agreed that the only such information is that described as such in Section 16 of this Agreement.

(e) As of the Applicable Time, the Disclosure Package did not include any untrue statement of material fact or omit to state any material fact necessary to make the statements therein, in light of the circumstances under which they were made, not misleading. The preceding sentence does not apply to statements in or omissions from any Pre-Pricing Prospectus in reliance upon and in conformity with written information furnished to the Company by any Underwriter through you specifically for use therein, it being understood and agreed that the only such information is that described as such in Section 16 of this Agreement.

(f) Each Covered Free Writing Prospectus, as of its issue date and at all subsequent times through the completion of the public offer and sale of the Shares or until any earlier date that the Company notified or notifies you as described in the next sentence, did not, does not and will not include any information that conflicted, conflicts or will conflict with the information then contained in the Registration Statement. If at

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any time following issuance of a Covered Free Writing Prospectus there occurred or occurs an event or development as a result of which such Covered Free Writing Prospectus conflicted or would conflict with the information then contained in the Registration Statement or as a result of which such Covered Free Writing Prospectus, if republished immediately following such event or development, would include an untrue statement of a material fact or omitted or would omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances prevailing at that subsequent time, not misleading, (i) the Company has promptly notified or will promptly notify you and (ii) the Company has promptly amended or will promptly amend or supplement such Covered Free Writing Prospectus to eliminate or correct such conflict, untrue statement or omission. The preceding sentences do not apply to statements in or omissions from any Covered Free Writing Prospectus in reliance upon and in conformity with written information furnished to the Company by any Underwriter through you specifically for use therein, it being understood and agreed that the only such information is that described as such in Section 16 of this Agreement.

(g) The accountants who certified the financial statements of the Company included or incorporated in the Registration Statement, the Prospectus and the Disclosure Package are independent public accountants as required by the Act.

(h) The consolidated financial statements of the Company together with related schedules and notes, included or incorporated in the Registration Statement, the Prospectus and the Disclosure Package present fairly the consolidated financial position of the Company and its subsidiaries as of the dates indicated and the results of their operations and the changes in their financial position for the periods specified; said financial statements have been prepared in conformity with generally accepted accounting principles consistently applied during the period, except as stated therein.

If applicable, the pro forma financial information set forth or incorporated by reference in the Registration Statement, the Prospectus and the Disclosure Package is, in all material respects, fairly presented and prepared on a basis consistent with the historical financial statements of the Company and its subsidiaries, except to the extent stated therein, and gives effect to assumptions used in the preparation thereof which have been made on a reasonable basis and in good faith.

(i) The Company has established and maintains disclosure controls and procedures (as such term in defined in Rule 13a-15 under the Exchange Act); such disclosure controls and procedures are designed to ensure that material information relating to the Company and its subsidiaries is made known to the chief executive officer and chief financial officer of the Company by others within the Company or any subsidiary, and such disclosure controls and procedures are reasonably effective to perform the functions for which they were established subject to the limitations of any such control system. The Company and each of its subsidiaries maintain a system of internal accounting controls sufficient to provide reasonable assurances that (A) transactions are executed in accordance with management’s general or specific authorization; (B) transactions are recorded as necessary to permit preparation of

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financial statements in conformity with generally accepted accounting principles and to maintain accountability for assets; (C) access to assets is permitted only in accordance with management’s general or specific authorization; and (D) the recorded accountability for assets is compared with the existing assets at reasonable intervals and appropriate action is taken with respect to any differences. The Company’s auditors and the audit committee of the board of directors of the Company have been advised of: (A) any significant deficiencies in the design or operation of internal controls which could adversely affect the Company’s ability to record, process, summarize, and report financial data; and (B) any fraud, whether or not material, that involves management or other employees who have a role in the Company’s internal controls; any material weaknesses in internal controls have been identified for the Company’s auditors; and since the date of the most recent evaluation of such disclosure controls and procedures, there have been no significant changes in internal controls or in other factors that could significantly affect internal controls, including any corrective actions with regard to significant deficiencies and material weaknesses. The Company made available to the Underwriters or their counsel for review true and complete copies of all minutes or draft minutes of meetings, or resolutions adopted by written consent, of the board of directors of the Company and each Significant Subsidiary and each committee of each such board in the past three years, and all agendas for each such meeting for which minutes or draft minutes do not exist.

(j) Except as described in the Disclosure Package as of the Applicable Time, since the date of the latest audited financial statements included or incorporated by reference in the Disclosure Package, there has been no change, nor any development or event involving a prospective change, in the financial condition, results of operations, business, properties or prospects of the Company and its subsidiaries, taken as a whole, that is material and adverse (a “ Material Adverse Change ”).

(k) Except as described in the Disclosure Package as of the Applicable Time, since the date of the latest audited financial statements included or incorporated by reference in the Disclosure Package, no litigation or governmental proceeding has been instituted or, to the knowledge of the Company, threatened against the Company or any subsidiary which would reasonably be expected to have any material adverse effect on the financial condition, results of operations, business, properties or prospects of the Company and its subsidiaries taken as a whole (a “ Material Adverse Effect ”).

(l) The Company has been duly incorporated and is validly existing as a corporation in good standing under the laws of the State of Delaware with the corporate power and authority to own, lease and operate its properties and conduct its business as described in the Prospectus and the Disclosure Package; and the Company is duly qualified or licensed to do business as a foreign corporation in good standing in each jurisdiction in which the conduct of its business or its ownership or leasing of property requires such qualification or licensing, except to the extent that the failure to be so qualified or licensed or be in good standing would not have a Material Adverse Effect.

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(m) Each significant subsidiary of the Company within the meaning of Regulation S-X (each “ Significant Subsidiary ”) is a duly incorporated or formed and validly existing corporation, partnership or limited liability company, as applicable, in good standing under the laws of its jurisdiction of incorporation or formation with full corporate, partnership or limited liability company power and authority to own, lease and operate its properties and conduct its business as described in the Prospectus and the Disclosure Package. Each Significant Subsidiary is duly qualified or licensed to do business as a foreign corporation, partnership or limited liability company in good standing in each jurisdiction in which the conduct of its business or its ownership or leasing of property requires such qualification or licensing, except to the extent that the failure to be so qualified or licensed or be in good standing would not have a Material Adverse Effect. The issued and outstanding common stock or other equity interests of each of the Significant Subsidiaries have been duly authorized and validly issued and are fully paid and non-assessable and, except as disclosed in the Prospectus and the Disclosure Package, are owned by the Company free and clear of any mortgages, liens or similar encumbrances.

(n) Neither the Company nor any Significant Subsidiary is (i) in violation of its certificate of incorporation or bylaws or similar organizational documents, (ii) in default in the performance or observance of any obligation in any indenture, mortgage, evidence of indebtedness or similar agreement or instrument to which it is a party or by which it or any of its properties may be bound or (iii) in violation of any law or statute or any judgment, order, rule or regulation of any court or arbitrator or governmental or regulatory authority, except, in the case of clauses (ii) and (iii) above, for any such default or violation that would not have a Material Adverse Effect. The execution and delivery of this Agreement, and the consummation of the transactions contemplated herein and therein and the incurrence of the obligations herein and therein set forth, have been or will be duly authorized by all necessary corporate action and do not and will not, conflict with, or constitute or result in a breach of or default under, the certificate of incorporation or bylaws of the Company or, except for any such conflict, breach or default which would not have a Material Adverse Effect, any law, order, rule, regulation or court decree or any bond, debenture, note or other evidence of indebtedness or any material contract, lease, license, indenture, mortgage, loan agreement or other agreement or instrument to which the Company or any of its subsidiaries is a party or by which the Company or any of its subsidiaries or any of their respective properties may be bound; and the Company has full corporate power and authority to issue and sell the Shares as contemplated by this Agreement.

(o) No consent, approval, authorization, order or qualification or registration of or with any court or governmental agency or body is required for the consummation of the transactions contemplated herein, except for (i) the registration of the offer and sale of the Shares under the Act and such consents, approvals, authorizations, orders, qualifications or registrations as may be required under the Blue Sky or securities laws of any jurisdiction in connection with the purchase and distribution of the Shares by the Underwriters; and (ii) such consents, approvals, authorizations, orders, qualifications or registrations, the failure of which to obtain or make would not individually or in the aggregate, have a Material Adverse Effect.

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(p) The Company and each Significant Subsidiary possess such valid franchises, certificates of convenience and necessity, easements, rights of way, operating rights, licenses, permits, consents, authorizations and orders of governmental political subdivisions or regulatory authorities as, in the opinion of the Company, are necessary to carry on the respective businesses of each as described in the Prospectus and the Disclosure Package, except where the failure to possess such would not have a Material Adverse Effect.

(q) Except as disclosed in the Disclosure Package and except for matters that would not, individually or in the aggregate, have a Material Adverse Effect: (i) the Company and its subsidiaries and their respective properties and operations are and, during the relevant time periods specified in all applicable statutes of limitations, have been in compliance with all applicable laws, rules, regulations, ordinances, codes, orders, and other legally enforceable requirements relating to the prevention of pollution, the preservation of environmental quality, the protection of natural resources, or the remediation of environmental contamination (collectively, “ Environmental Laws ”); (ii) the Company and its subsidiaries and their respective properties and operations are not subject to any proceeding, lawsuit, or other legal action or, to the Company’s knowledge, any investigation or inquiry, by or before any governmental authority pursuant to any Environmental Law; (iii) the Company and its subsidiaries and their respective properties and operations are not subject to any liability (including any obligation to perform any investigatory, corrective or remedial action that has been asserted) pursuant to Environmental Laws in connection with any release into the environment of, or any exposure of any person or property to, any pollutant, contaminant, solid or hazardous waste, hazardous or toxic substance, or any other material regulated under Environmental Laws.

(r) Except as disclosed in the Disclosure Package and the Prospectus, the Company and its subsidiaries have (i) generally satisfactory title to their oil and gas properties, title investigations having been carried out by the Company in accordance with the practice in the oil and gas industries in the areas in which the Company operates, (ii) good and marketable title to all other real property owned by them to the extent necessary to carry on their business and (iii) good and marketable title to all personal property owned by them, in each case free from liens, encumbrances and defects that would materially affect the value thereof or materially interfere with the use made or to be made thereof by them; and except as disclosed in the Disclosure Package and the Prospectus, the Company and its subsidiaries hold any leased real or personal property under valid and enforceable leases with no exceptions that would materially interfere with the use made or to be made thereof by them.

(s) (i) The oil and natural gas reserve estimates of the Company and its subsidiaries, as of December 31, 2006, 2007 and 2008 contained in the Disclosure Package and the Prospectus are derived from reports by the Company and reviewed by Netherland, Sewell & Associates, Inc. or Miller and Lents, Ltd., as set forth and to the extent indicated therein, and (ii) such estimates reasonably reflect the oil and natural gas

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reserves of the Company and its subsidiaries, as applicable, at the dates indicated therein and are in accordance, in all material respects, with Commission guidelines applied on a consistent basis throughout the periods involved.

(t) Each of Miller and Lents, Ltd. and Netherland, Sewell & Associates, Inc. have represented to the Company that they are, and the Company believes them to be, independent petroleum engineers with respect to the Company and its subsidiaries and for the periods set forth in the Disclosure Package and the Prospectus.

(u) This Agreement has been duly authorized, executed and delivered by the Company.

(v) The Shares have been duly and validly authorized and, when issued and delivered against payment therefor as provided herein, will be duly and validly issued, fully paid and non-assessable and free of statutory and contractual preemptive rights, resale rights, rights of first refusal and similar rights; the Shares, when issued and delivered against payment therefor as provided herein, will be free of any restriction upon the voting or transfer thereof pursuant to the Delaware General Corporation Law or the Company’s charter or bylaws or any agreement or other instrument to which the Company is a party.

(w) The documents incorporated by reference in the Registration Statement, the Disclosure Package and the Prospectus, when they were filed with the Commission conformed in all material respects to the requirements of the Exchange Act and none of such documents contained any untrue statement of a material fact or omitted to state a material fact required to be stated therein or necessary to make the statements therein, in light of the circumstances under which they were made, not misleading; and any further documents so filed and incorporated by reference in the Registration Statement, the Disclosure Package and the Prospectus, when such documents become effective or are filed with the Commission, as the case may be, will conform in all material respects to the requirements of the Act or the Exchange Act, as applicable, and will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein, in light of the circumstances under which they were made, not misleading.

(x) As of the date of this Agreement, the Company has an authorized and outstanding capitalization as set forth in the sections of the Registration Statement, the Pre-Pricing Prospectuses and the Prospectus entitled “Capitalization” and “Description of Common Stock” (and any similar sections or information, if any, contained in any Permitted Free Writing Prospectus), and, as of the time of purchase and any additional time of purchase, as the case may be, the Company shall have an authorized and outstanding capitalization as set forth in the sections of the Registration Statement, the Pre-Pricing Prospectuses and the Prospectus entitled “Capitalization” and “Description of Common Stock” (and any similar sections or information, if any, contained in any Permitted Free Writing Prospectus) (subject, in each case, to the issuance of shares of Common Stock upon exercise of stock options and warrants disclosed as outstanding in

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the Registration Statement (excluding the exhibits thereto), each Pre-Pricing Prospectus and the Prospectus and the grant of options under existing stock option plans described in the Registration Statement (excluding the exhibits thereto), each Pre-Pricing Prospectus and the Prospectus). All of the issued and outstanding shares of capital stock, including the Common Stock, of the Company have been duly authorized and validly issued and are fully paid and non-assessable, have been issued in compliance with all applicable securities laws and were not issued in violation of any preemptive right, resale right, right of first refusal or similar right. The Shares are duly listed, and admitted and authorized for trading, subject to official notice of issuance, on the NYSE.

(y) The capital stock of the Company, including the Shares, conforms in all material respects to each description thereof, if any, contained or incorporated by reference in the Registration Statement, the Pre-Pricing Prospectuses, the Prospectus and the Permitted Free Writing Prospectuses, if any, for the Shares are in due and proper form.

(z) Except as described in the Registration Statement (excluding the exhibits thereto), each Pre-Pricing Prospectus and the Prospectus, (i) no person has the right, contractual or otherwise, to cause the Company to issue or sell to it any shares of Common Stock or shares of any other capital stock or other equity interests of the Company, (ii) no person has any preemptive rights, resale rights, rights of first refusal or other rights to purchase any shares of Common Stock or shares of any other capital stock of or other equity interests in the Company and (iii) no person has the right to act as an underwriter or as a financial advisor to the Company in connection with the offer and sale of the Shares. No person has the right, contractual or otherwise, to cause the Company to register under the Act any shares of Common Stock or shares of any other capital stock of or other equity interests in the Company, or to include any such shares or interests in the Registration Statement or the offering contemplated thereby (other than demand registration rights with respect to 4,000,000 shares as set forth in the Anadarko Petroleum Corporation Benefits Trust Agreement, amended and restated effective as of November 25, 2008).

(aa) The Company has obtained for the benefit of the Underwriters the agreement (a “ Lock-Up Agreement ”), in the form set forth as Exhibit A hereto, of each of the persons listed on Exhibit A-1 hereto.

(bb) Neither the Company nor any of its subsidiaries is, and at no time during which a prospectus is required by the Act to be delivered (whether physically or through compliance with Rule 172 under the Act or any similar rule) in connection with any sale of Shares will either of them be, and, after giving effect to the offering and sale of the Shares and the application of the proceeds thereof, neither of them will be, an “investment company” or an entity “controlled” by an “investment company,” as such terms are defined in the Investment Company Act of 1940, as amended.

(cc) The issuance and sale of the Shares as contemplated hereby will not cause any holder of any shares of capital stock, securities convertible into or exchangeable or

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exercisable for capital stock or options, warrants or other rights to purchase capital stock or any other securities of the Company to have any right to acquire any shares of preferred stock of the Company.

(dd) The Company has not received any notice from the NYSE regarding the delisting of the Common Stock from the NYSE.

In addition, any certificate signed by any officer of the Company or any of its subsidiaries and delivered to any Underwriter or counsel for the Underwriters in connection with the offering of the Shares shall be deemed to be a representation and warranty by the Company, as to matters covered thereby, to each Underwriter.

4. Certain Covenants of the Company . The Company covenants with each of you, and with each Underwriter participating in the offering of Shares, as follows with respect to such offering of Shares:

(a) As soon as practicable, following the execution of this Agreement, the Company will prepare the Prospectus setting forth the number of Shares covered thereby, the names of the Underwriters participating in the offering and the number of Shares which each severally has agreed to purchase, the names of the Underwriters acting as co-managers in connection with the offering, the price at which the Shares are to be purchased by the Underwriters from the Company, the public offering price of the Shares, if applicable, the selling concession and reallowance applicable to the Shares, if any, any Additional Shares information and such other information as you and the Company deem appropriate in connection with the offering of the Shares. The Company will transmit copies of the Prospectus to the Commission in compliance with Rule 424 under the Act and will furnish to the Underwriters named therein as many copies of the Prospectus and the Disclosure Package as you shall reasonably request for the purposes contemplated by the Act.

(b) If at any time when the Prospectus (or in lieu thereof the notice referred to in Rule 173(a) under the Act) is required by the Act to be delivered in connection with sales of such Shares any event shall occur or condition exist as a result of which it is necessary to further amend or supplement the Prospectus in order that the Prospectus will not include an untrue statement of a material fact or omit to state any material fact necessary to make the statements therein not misleading in the light of circumstances existing at the time it is delivered to a purchaser or if it shall be necessary at any time to amend or supplement the Registration Statement or the Prospectus in order to comply with the requirements of the Act, the Company will, as soon as practicable, prepare and file (if required) with the Commission such amendment or supplement, whether by filing documents pursuant to the Exchange Act or otherwise, as may be necessary to correct such untrue statement or omission or to make the Registration Statement comply with such requirements.

(c) If the Disclosure Package is being used to solicit offers to buy the Shares at a time when the Prospectus is not yet available to prospective purchasers and any event

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shall occur or condition exist as a result of which it is necessary to amend or supplement the Disclosure Package in order to make the statements therein, in the light of the circumstances under which they were made, not misleading, or if any event shall occur or condition exist as a result of which the Disclosure Package conflicts with the information contained in the Registration Statement then on file, or if, in the opinion of counsel for the Underwriters, it is necessary to amend or supplement the Disclosure Package to comply with applicable law, the Company will prepare, file with the Commission and furnish, at its own expense, to the Underwriters and to any dealer upon request, either amendments or supplements to the Disclosure Package so that the statements in the Disclosure Package as so amended or supplemented will not contain any statement of untrue material fact or omit to state a material fact necessary in order to make the statements not misleading, in the light of the circumstances when delivered to a prospective purchaser, or so that the Disclosure Package, as amended or supplemented, will no longer conflict with the Registration Statement, or so that the Disclosure Package, as amended or supplemented, will comply with applicable law.

(d) The Company will make generally available to its security holders as soon as practicable, but in any event not later than 18 months after the date of this Agreement relating to the Shares, earnings statements of the Company and its subsidiaries (which need not be audited) complying with Section 11(a) of the Act (including, at the option of the Company, Rule 158 under the Act).

(e) The Company, during the period when the Prospectus is required by the Act to be delivered in connection with sales of such Shares, will, except in the case of reports filed pursuant to the Exchange Act, give you notice of its intention to file any amendment to the Registration Statement or any amendment or supplement to the Prospectus or the Disclosure Package, whether pursuant to the Act or otherwise and will furnish you with copies of any such amendment or supplement or other documents proposed to be filed in a reasonable time for review by the Underwriters in advance of filing.

(f) The Company, during the period when the Prospectus is required by the Act to be delivered by you in connection with sales of Shares, will notify each of you, as soon as practicable, and confirm the notice in