CONTRIBUTION AGREEMENT

Exhibit 2.1

Execution Version

CONTRIBUTION AGREEMENT

by and among

ANADARKO UINTAH MIDSTREAM, LLC
WESTERN GAS RESOURCES, INC.
WGR HOLDINGS, LLC
WGR ASSET HOLDING COMPANY LLC
WESTERN GAS HOLDINGS, LLC
WES GP, INC.

as Contributing Parties

and

WESTERN GAS PARTNERS, LP
WESTERN GAS HOLDINGS, LLC
WESTERN GAS OPERATING, LLC
WGR OPERATING, LP

as Recipient Parties

and, for certain limited purposes,
ANADARKO PETROLEUM CORPORATION

Covering the Contribution of

a 51% membership interest in Chipeta Processing LLC;
the 15-mile, 8” AUM NGL pipeline; and
certain other related rights and assets

Dated as of July 10, 2009

TABLE OF CONTENTS

Disclosure Schedules

Exhibits

CONTRIBUTION AGREEMENT

     THIS CONTRIBUTION AGREEMENT, dated as of July 10, 2009 (the “ Agreement ”), is made and entered into by and among Western Gas Resources, Inc., a Delaware corporation (“ WGR ”), WGR Asset Holding Company LLC, a Delaware limited liability company (“ WGRAH ”), Anadarko Uintah Midstream, LLC, a Delaware limited liability company (“ AUM ”), WGR Holdings, LLC, a Delaware limited liability company (“ WGR Holdings ”), Western Gas Holdings, LLC, a Delaware limited liability company (the “ General Partner ”), WES GP, Inc. (“ WES GP ” and, together with the General Partner, WGR, WGRAH, WGR Holdings and AUM, the “ Contributing Parties ”), and Western Gas Partners, LP, a Delaware limited partnership (the “ Partnership ”), Western Gas Operating, LLC, a Delaware limited liability company (“ Western Gas Operating ”), and WGR Operating, LP, a Delaware limited partnership (the “ Operating Partnership ”, and, together with the Partnership, the General Partner and Western Gas Operating, the “ Recipient Parties ”). The Contributing Parties and Recipient Parties are sometimes referred to in this Agreement each as a “ Party ” and collectively as the “ Parties .” In addition, Anadarko Petroleum Corporation, a Delaware corporation (“ Anadarko ”), is a party to this Agreement for the limited purposes set forth in Article II , Article IV , Section 6.6 , Article VIII and Article IX , and is a “Party” under this Agreement solely to that extent.

RECITALS

     WHEREAS, WGR owns all of the equity interests in WGRAH and WGR Holdings, each of which is a disregarded entity for U.S. federal income tax purposes;

     WHEREAS, WGRAH owns all of the equity interests in AUM;

     WHEREAS, WGR Holdings owns 99% of the equity interests in the General Partner, which is a partnership for U.S. federal income tax purposes;

     WHEREAS, WGR Holdings owns all of the equity interests in WES GP, which is a corporation for federal income tax purposes;

     WHEREAS, WES GP owns 1% of the equity interests in the General Partner;

     WHEREAS, WGR Holdings is a limited partner of the Partnership;

     WHEREAS, the General Partner is the sole general partner of the Partnership;

     WHEREAS, the Partnership owns all of the equity interests in Western Gas Operating, which is a disregarded entity for U.S. federal income tax purposes;

     WHEREAS, the Partnership is the sole limited partner and Western Gas Operating is the sole general partner of the Operating Partnership;

     WHEREAS, AUM owns the AUM NGL Line (defined herein) and the related System Assets (defined herein);

     WHEREAS, AUM will acquire the Stagecoach Extension (defined herein) and the related System Assets (defined herein) prior to Closing;

     WHEREAS, AUM also owns the Chipeta Interest (defined herein);

     WHEREAS, AUM desires to distribute the System Assets and the Chipeta Interest to WGRAH and WGRAH desires to acquire the same;

     WHEREAS, WGRAH desires to distribute the System Assets and the Chipeta Interest to WGR and WGR desires to acquire the same;

     WHEREAS, WGR desires to contribute the System Assets and the Chipeta Interest to WGR Holdings and WGR Holdings desires to acquire the same;

     WHEREAS, WGR Holdings desires to contribute an undivided interest in the System Assets and the Chipeta Interest to WES GP, and WES GP desires to acquire such undivided interest;

     WHEREAS, WES GP desires to contribute such undivided interest in the System Assets and the Chipeta Interest to the General Partner, and the General Partner desires to acquire such undivided interest;

     WHEREAS, WGR Holdings desires to contribute an undivided interest in the System Assets and the Chipeta Interest to the General Partner, and the General Partner desires to acquire such undivided interest;

     WHEREAS WGR Holdings and the General Partner desire to contribute all of the undivided interests in the System Assets and the Chipeta Interest to the Partnership for the consideration described herein, and the Partnership desires to acquire such undivided interests for such consideration;

     WHEREAS, the Partnership desires to contribute an undivided interest in the System Assets and the Chipeta Interest to Western Gas Operating, and Western Gas Operating desires to acquire such undivided interest;

     WHEREAS, the Partnership and Western Gas Operating desire to transfer all of the undivided interests in the System Assets and the Chipeta Interest to the Operating Partnership and the Operating Partnership desires to acquire such undivided interests; and

     WHEREAS, in order to avoid multiple conveyances of the System Assets and the Chipeta Interest, each of the Parties entitled to receive an interest in the System Assets and the Chipeta Interest agrees that AUM will be instructed to convey such interest to any Party to which it is required to make such a conveyance, with the result that AUM will execute and deliver a document to convey legal title to the System Assets and the Chipeta Interest directly to the Operating Partnership.

     NOW, THEREFORE, in consideration of the premises and mutual covenants contained herein and other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the Parties agree as follows:

ARTICLE I
DEFINITIONS AND RULES OF CONSTRUCTION

     Section 1.1 Definitions .

     “ Accounting Time ” has the meaning set forth in Section 3.4(a) .

     “ Affiliate ” means, with respect to any Person, any other Person that, directly or indirectly, Controls, is Controlled by or is under common Control with, such specified Person through one or more intermediaries or otherwise; provided , however , that (i) with respect to each of the Anadarko Entities and the Contributing Parties, the term “Affiliate” shall exclude the Partnership Entities, (ii) with respect to each of the Partnership Entities and the Recipient Parties, the term “Affiliate” shall exclude the Anadarko Entities, and (iii) Chipeta shall be deemed to be an Affiliate of the Anadarko Entities before the Closing Date and an Affiliate of the Partnership Entities on and after the Closing Date.

     “ Aggregate Consideration ” has the meaning set forth in Section 9.8(a) .

     “ Agreement ” has the meaning set forth in the preamble.

     “ Anadarko ” has the meaning set forth in the preamble.

     “ Anadarko Entities ” means Anadarko and any other Person Controlled by Anadarko other than the Partnership Entities.

     “ Anadarko Indemnified Parties ” has the meaning set forth in Section 9.2 .

     “ Ancillary Documents ” means, collectively, the Recipient Party Ancillary Documents and the Contributing Party Ancillary Documents.

     “ Annual Financial Statements ” has the meaning set forth in Section 4.15 .

     “ AUM ” has the meaning set forth in the preamble.

     “ AUM NGL Line ” means the approximately 15-mile, 8-inch NGL pipeline (including all appurtenances thereto) connecting the Chipeta Plant to the pipeline known as the “Mid-America Pipeline,” which NGL pipeline is more specifically described on Exhibit B .

     “ Business Day ” means any day that is not a Saturday, Sunday or legal holiday in the State of Texas or a federal holiday in the United States.

     “ Cash Consideration ” means (i) $101,450,500 minus (ii) an amount equal to the aggregate amount of all distributions (if any) made by Chipeta to AUM with respect to the Chipeta Interest (but not the Remaining Interest) between the date of this Agreement and the

Closing Date, except to the extent that such distributions were regular quarterly distributions required by Section 4.2 of the Chipeta LLC Agreement for quarters ended prior to the Effective Time.

     “ Chipeta ” means Chipeta Processing LLC, a Delaware limited liability company.

     “ Chipeta Assets ” means the Chipeta Plant and the other assets owned, held, used or held for use by Chipeta, which other assets are more specifically described on Exhibit D .

     “ Chipeta Asset Required Consents ” means any consent, approval, authorization or permit of, or filing with or notification to, any Person which was required to be obtained, made or complied with for or in connection with any sale, assignment or transfer to Chipeta of any Chipeta Asset or any Chipeta Surface Contract (or any interest in any of them), and such required consent, approval, authorization, permit, filing or notificiation has not been obtained, made or complied with prior to Closing.

     “ Chipeta LLC Agreement ” means the limited liability company agreement of Chipeta, dated May 22, 2008, as such agreement is amended and in effect on the date of this Agreement.

     “ Chipeta Contracts ” means all contracts, agreements, instruments, undertakings or commitments (including intercompany contracts, agreements, instruments, undertakings or commitments), written or oral, by which Chipeta or any of its properties or assets are bound, or that relate to or are otherwise applicable to Chipeta or the Chipeta Assets (including exchange agreements, transportation or gathering agreements, construction agreements, operating agreements, environmental compliance agreements, processing agreements, work orders, purchase orders, service agreements, rental agreements, compression agreements, utility services agreements, non-disturbance agreements for the benefit of the Chipeta, fractionation agreements, and agreements for the sale and purchase of oil, gas, casinghead gas or other Hydrocarbons or processing agreements to the extent applicable to Chipeta or any of its properties or assets).

     “ Chipeta Interest ” means a 51% membership interest in Chipeta.

     “ Chipeta Interest Contribution Agreement ” means a conveyance, substantially in the form attached hereto as Exhibit F , reflecting the contribution of the Chipeta Interest to the Operating Partnership.

     “ Chipeta Permits ” has the meaning set forth in Section 4.11(c).

     “ Chipeta Plant ” means the Chipeta natural gas processing plant (including all appurtenances thereto), which plant is more specifically described on Exhibit A .

     “ Chipeta Surface Contracts ” means all easements, Chipeta Permits, licenses, servitudes, rights-of-way, surface leases, fee interests in real property and other surface rights appurtenant to, and used or held for use in connection with Chipeta or the Chipeta Assets, including those identified on Schedule 4.6(d) .

     “ CIG ” means Colorado Interstate Gas Company.

     “ CIG Purchase Agreement ” means that certain Purchase and Sale Agreement dated November 21, 2008 between CIG and Chipeta.

     “ Closing ” has the meaning set forth in Section 3.1 .

     “ Closing Date ” has the meaning set forth in Section 3.1 .

     “ Code ” means the Internal Revenue Code of 1986, as amended and as interpreted by the applicable Treasury Regulations thereunder.

     “ Consent Decree ” has the meaning set forth in Section 9.3 .

     “ Contracts ” has the meaning set forth in Section 2.1(b) .

     “ Contributed Assets ” has the meaning set forth in Section 2.7(a) .

     “ Contributing Party Ancillary Documents ” means each agreement, document, instrument or certificate to be delivered by any Contributing Party, or any Affiliate thereof, at the Closing pursuant to Section 3.2 and each other document or contract entered into by any Contributing Party, or any Affiliate thereof, in connection with this Agreement or the Closing.

     “ Contributing Parties ” has the meaning set forth in the preamble.

     “ Contributing Party Closing Certificate ” has the meaning set forth in Section 7.2(c) .

     “ Control ” means, where used with respect to any Person, the possession, directly or indirectly, of the power to direct or cause the direction of the management and policies of such Person, whether through the ownership of voting securities, by contract or otherwise, and the terms “ Controlling ” and “ Controlled ” have correlative meanings.

     “ Deductible ” has the meaning set forth in Section 9.8(a) .

     “ Effective Time ” has the meaning set forth in Section 3.1 .

     “ Environmental Activity ” shall mean any investigation, study, assessment, evaluation, sampling, testing, monitoring, containment, removal, disposal, closure, corrective action, remediation (regardless of whether active or passive), natural attenuation, restoration, bioremediation, response, repair, corrective measure, cleanup, pollution control or abatement that is required or necessary under any applicable Environmental Law, including institutional or engineering controls or participation in a governmental voluntary cleanup program to conduct voluntary investigatory and remedial actions for the clean-up, removal or remediation of Hazardous Substances that exceed actionable levels established pursuant to Environmental Laws, or participation in a supplemental environmental project in partial or whole mitigation of a fine or penalty.

     “ Environmental Laws ” means all federal, state, and local laws, statutes, rules, regulations, orders, judgments, ordinances, codes, injunctions, decrees, Environmental Permits and other legally enforceable requirements and rules of common law relating to (i) pollution or

protection of the environment or natural resources, (ii) any Release or threatened Release of, or any exposure of any Person or property to, any Hazardous Substances or (iii) the generation, manufacture, processing, distribution, use, treatment, storage, transport, disposal or handling of any Hazardous Substances; including the federal Comprehensive Environmental Response, Compensation and Liability Act, the Superfund Amendments and Reauthorization Act, the Resource Conservation and Recovery Act, the Clean Air Act, the Clean Water Act, the Safe Drinking Water Act, the Toxic Substances Control Act, the Oil Pollution Act of 1990, the Federal Hazardous Materials Transportation Law, the Occupational Safety and Health Act, the Marine Mammal Protection Act, the Endangered Species Act, the National Environmental Policy Act and other environmental conservation and protection laws, each as amended through the Closing Date.

     “ Environmental Permit ” means any permit, approval, identification number, license, registration, certification, consent, exemption, variance or other authorization required under or issued pursuant to any applicable Environmental Law.

     “ Equipment ” has the meaning set forth in Section 2.1(d) .

     “ Equity Interest ” means any capital stock, partnership interest, membership interest or other unit of equity security, equity ownership or voting security (including any security convertible into or exchangeable or exercisable for any of the same).

     “ Excluded Assets ” has the meaning set forth in Section 2.2 .

     “ Final Settlement Statement ” has the meaning set forth in Section 2.6(b) .

     “ Financial Statements ” has the meaning set forth in Section 4.15 .

     “ GAAP ” means generally accepted accounting principles in the United States, consistently applied.

     “ General Partner ” has the meaning set forth in the preamble.

     “ Governmental Entity ” means any Federal, state, local, municipal or foreign court or governmental agency, authority or instrumentality or regulatory body having jurisdiction.

     “ GP Consideration ” means 7,172 general partner units of the Partnership.

     “ Hazardous Substance ” means (i) any substance that is designated, defined or classified under any Environmental Law as a hazardous waste, solid waste, hazardous material, pollutant, contaminant or toxic or hazardous substance, or terms of similar meaning, or that is otherwise regulated under any Environmental Law, including any hazardous substance as defined under the Comprehensive Environmental Response, Compensation, and Liability Act, as amended, (ii) oil as defined in the Oil Pollution Act of 1990, as amended, including oil, gasoline, natural gas, fuel oil, motor oil, waste oil, diesel fuel, jet fuel and other refined petroleum hydrocarbons and petroleum products and (iii) radioactive materials, asbestos containing materials or polychlorinated biphenyls.

     “ Hydrocarbons ” means oil, gas, condensate and other gaseous and liquid hydrocarbons or any combination thereof and sulphur extracted from hydrocarbons.

     “ Indemnified Party ” means any Person entitled to indemnification in accordance with Article IX .

     “ Indemnifying Party ” means any Person from whom indemnification is required in accordance with Article IX .

     “ Indemnity Claim ” has the meaning set forth in Section 9.4 .

     “ Independent Accountants ” has the meaning set forth in Section 2.6(c) .

     “ Interim Financial Statements ” has the meaning set forth in Section 4.15 .

     “ Knowledge ” and any variations thereof or words to the same effect means: (i) with respect to the Contributing Parties, the actual knowledge of: (a) the officers of the Contributing Parties and their respective Affiliates, (b) the employees of Contributing Parties who have responsibility for the System Assets and who have the title of Midstream General Manager or Midstream Commercial Development Regional Manager and (c) the employees of Contributing Parties who have responsibility for Chipeta and who have the title of Midstream General Manager or Midstream Commercial Development Regional Manager; and (ii) with respect to the Recipient Parties, the actual knowledge of the officers of Recipient Parties and their respective Affiliates.

     “ Laws ” means all statutes, laws, rules, regulations, Orders, ordinances, writs, injunctions, judgments and decrees of all Governmental Entities.

     “ Lien ” means any lien, security interest, mortgage, pledge, charge, encumbrance or right of others.

     “ Losses ” means any losses, damages, liabilities, claims, demands, causes of action, judgments, settlements, fines, penalties, sanctions, costs and expenses (including court costs and reasonable attorney’s and experts’ fees) of any and every kind or character.

     “ Material Adverse Effect ” means any effect that is material and adverse to the ownership, operation, value, properties, assets, liabilities, financial condition, results of operations, or business (as currently operated) of (a) Chipeta, the Chipeta Assets or the Chipeta Interest or (b) the Systems or the assets related thereto, or the Contributing Parties’ interest therein; provided , however , that “Material Adverse Effect” shall not include (i) any effect resulting from the announcement of entering into this Agreement or of the transactions contemplated by this Agreement; (ii) any effect resulting from changes in general market, economic or financial conditions or any outbreak of hostilities or war, (iii) any effect that affects the Hydrocarbon exploration, production, development, processing, gathering and/or transportation industry generally (including changes in commodity prices or general market prices in the Hydrocarbon exploration, production, development, processing, gathering and/or transportation industry generally) unless such effect disproportionately affects Chipeta, the

Chipeta Plant, the Chipeta Interest or the Systems, as applicable, relative to such industry, and (iv) any effect resulting from a change in Laws.

     “ NORM ” means naturally occurring radioactive material.

     “ Omnibus Agreement ” means the Omnibus Agreement dated as of May 14, 2008 among the Partnership, the General Partner and Anadarko, as amended through the date of this Agreement.

     “ Omnibus Agreement Amendment ” means an instrument substantially in the form set forth on Exhibit I .

     “ Operating Costs ” means all invoices, costs, expenses, disbursements and payables (as determined in accordance with GAAP consistent with past practices) attributable to the operation (but not the ownership) of the System Assets in the ordinary course of business and regularly invoiced to the Contributing Parties. For clarity, Operating Costs do not include, without limitation, all invoices, costs, expenses, disbursements, payables or Losses directly or indirectly arising out of, resulting from or attributable to: (i) actual or claimed personal injury, illness or death; property damage; environmental damage or contamination; negligence, misconduct or failure to operate properly; other torts; private rights of action given under any Law; violation of any Law; or breach or violation of contract, agreement or duty; (ii) obligations to abandon, dismantle, remediate or remove pipelines or facilities; (iii) calamity, natural disaster, casualty, fire, explosion, weather or condemnation; (iv) claims, investigations, administrative proceedings, arbitration or litigation directly or indirectly arising out of, resulting from or attributable to any of the foregoing; (v) any claims for any of the foregoing or for indemnification, contribution, reimbursement or similar matters with respect to invoices, costs, expenses, disbursements, payables or Losses of the type described in clauses (i) through (iv), whether such claims are made pursuant to contract or otherwise; (vi) matters similar to those described in clauses (i) through (v); and (vii) other matters outside the ordinary course of business or related to the ownership of the System Assets.

     “ Operating Partnership ” has the meaning set forth in the preamble.

     “ Order ” means any order, writ, injunction, decree, ruling, compliance or consent order or decree, settlement agreement, schedule and similar binding legal agreement issued by or entered into with a Governmental Entity.

     “ Partnership ” has the meaning set forth in the preamble.

     “ Partnership Agreement Amendment ” means an instrument substantially in the form set forth on Exhibit H .

     “ Partnership Agreement ” means the First Amended and Restated Agreement of Limited Partnership of the Partnership, dated as of May 14, 2008, as such agreement is amended and in effect on the date of this Agreement.

     “ Partnership Debt ” has the meaning set forth in Section 2.5 .

     “ Partnership Entities ” means the General Partner and each member of the Partnership Group.

     “ Partnership Group ” means the Partnership and its Subsidiaries treated as a single consolidated entity.

     “ Partnership Indemnified Parties ” has the meaning set forth in Section 9.3 .

     “ Party ” and “ Parties ” have the meanings set forth in the preamble.

     “ Permits ” means all permits, licenses, variances, exemptions, Orders, franchises, consents, registrations, exemptions, authorizations, permissions and approvals of all Governmental Entities necessary for the lawful ownership, lease and operation of the System Assets.

     “ Permitted Liens ” means (i) liens for Taxes, impositions, assessments, fees, rents or other governmental charges levied or assessed or imposed not yet delinquent or being contested in good faith by appropriate proceedings, provided appropriate reserves have been established with respect to such contest, (ii) statutory liens (including materialmen’s, warehousemen’s, mechanics’, repairmen’s, landlord’s, and other similar liens) arising in the ordinary course of business securing payments not yet delinquent or being contested in good faith by appropriate proceedings, and (iii) utility easements, restrictive covenants and defects, imperfections or irregularities of title that do not and could not reasonably be expected to interfere materially with the ordinary conduct of the business of the System Assets or Chipeta.

     “ Person ” means any individual, firm, corporation, partnership (general or limited), limited liability company, trust, joint venture, Governmental Entity or other entity.

     “ Post Closing Consents ” means (i) any consent, approval or permit of, or filing with or notice to, any Governmental Entity, railroad company or public utility which has issued or granted any permit, license, right of way, lease or other authorizations permitting any part of any pipeline included in the System Assets to cross or be placed on land owned or controlled by such Governmental Entity, railroad company or public utility and (ii) any consent, approval or permit of, or filing with or notice to, any Governmental Entity or other third party with respect to any System Assets that, in the case of both clause (i) and (ii), is customarily obtained or made after closing in connection with transactions similar in nature to the transactions contemplated hereby.

     “ Preference Right ” means any right or agreement that enables any Person to purchase or acquire any System Asset, the Chipeta Interest or any properties or assets of Chipeta (or any interest in or portion of any of them) as a result of or in connection with (i) the sale, assignment or other transfer of any System Asset, the Chipeta Interest or any properties or assets of Chipeta (or any interest in or portion of any of them) or (ii) the execution or delivery of this Agreement or the consummation or performance of this Agreement or the transactions contemplated hereby.

     “ Preliminary Settlement Statement ” has the meaning set forth in Section 2.6(a) .

     “ Recipient Party Ancillary Documents ” means each agreement, document, instrument or certificate to be delivered by any Recipient Party, or any Affiliate thereof, at the Closing

pursuant to Section 3.3 and each other document or contract entered into by any Recipient Party, or any Affiliate thereof, in connection with this Agreement or the Closing.

     “ Recipient Parties ” has the meaning set forth in the preamble.

     “ Recipient Party Closing Certificate ” has the meaning set forth in Section 7.3(b) .

     “ Records ” has the meaning set forth in Section 2.1(i) .

     “ Release ” means any depositing, spilling, leaking, pumping, pouring, placing, emitting, discarding, abandoning, emptying, discharging, migrating, injecting, escaping, leaching, dumping or disposing into the environment.

     “ Remaining Interest ” means the 24% membership interest in Chipeta owned by AUM other than the Chipeta Interest.

     “ Securities Act ” means the Securities Act of 1933.

     “ Settlement Notice ” has the meaning set forth in Section 2.6(c) .

     “ Services and Secondment Agreement ” means the Services and Secondment Agreement dated as of May 14, 2008 by and between the General Partner and Anadarko, as such agreement is amended and in effect on the date of this Agreement.

     “ Special Committee ” has the meaning set forth in the Partnership Agreement.

     “ Stagecoach Agreement ” means the Interconnect Agreement dated July 21, 2008 between AUM and Questar Gas Management Company.

     “ Stagecoach Extension ” means the approximately 1.9-mile, 6-inch pipeline extension (including all appurtenances thereto) connecting the Chipeta Plant to the plant generally known as the “Stagecoach plant”, which pipeline extension is more specifically described on Exhibit C .

     “ Subsidiary ” means, with respect to any Person, (i) a corporation of which more than 50% of the voting power of shares entitled (without regard to the occurrence of any contingency) to vote in the election of directors or other governing body of such corporation is owned, directly or indirectly, at the date of determination, by such Person, by one or more Subsidiaries of such Person or a combination thereof, (ii) a partnership (whether general or limited) in which more than 50% of the partnership interests (considering all of the partnership interests of the partnership as a single class) is owned, directly or indirectly, at the date of determination, by such Person, by one or more Subsidiaries of such Person, or a combination thereof, or (iii) any other Person (other than a corporation or a partnership) in which such Person, one or more subsidiaries of such Person, or a combination thereof, directly or indirectly, at the date of determination, has (A) at least a majority ownership interest or (B) the power to elect or direct the election of a majority of the directors or other governing body of such Person.

     “ Surface Contracts ” has the meaning set forth in Section 2.1(c) .

     “ System Assets ” has the meaning set forth in Section 2.1 .

     “ System Asset Conveyances ” means instruments substantially in the forms attached hereto as Exhibit G .

     “ System Asset Required Consents ” means any consent, approval, authorization or permit of, or filing with or notification to, any Person which was required to be obtained, made or complied with for or in connection with any sale, assignment or transfer pursuant to this Agreement (or any interest in any of them), and such required consent, approval, authorization, permit, filing or notificiation has not been obtained, made or complied with prior to Closing.

     “ Systems ” means the AUM NGL Line and the Stagecoach Extension.

     “ Tax ” or “ Taxes ” means (a) all taxes, assessments, duties, levies, imposts or other similar charges imposed by a Governmental Entity, including all income, franchise, profits, capital gains, capital stock, transfer, gross receipts, margins, sales, use, transfer, service, occupation, ad valorem, property, excise, severance, windfall profits, premium, stamp, license, payroll, employment, social security, unemployment, disability, environmental (including taxes under Code Section 59A), alternative minimum, add-on, value-added, withholding (including backup withholding) and other taxes, assessments, duties, levies, imposts or other similar charges of any kind whatsoever (whether payable directly or by withholding and whether or not requiring the filing of a Tax Return), and all estimated taxes, deficiency assessments, additions to tax, additional amounts imposed by any Governmental Entity, penalties and interest, (b) any liability for the payment of any amounts of any of the foregoing types as a result of being a member of an affiliated, consolidated, combined or unitary group, or being a party to any agreement or arrangement whereby liability for payment of such amounts was determined or taken into account with reference to the liability of any other Person, and (c) any liability for the payment of any amounts as a result of being a party to any Tax-Sharing Agreement or with respect to the payment of any amounts of any of the foregoing types as a result of any express or implied obligation to indemnify any other Person.

     “ Tax Authority ” means any Governmental Entity having jurisdiction over the assessment, determination, collection or imposition of any Tax.

     “ Tax Returns ” means all reports, returns, statements (including estimated reports, returns or statements) and other similar filings relating to, or required to be filed in connection with, any Taxes.

     “ Tax-Sharing Agreements ” means all existing contracts or arrangements (whether or not written) regarding the sharing, allocation, or payment of Taxes or amounts in lieu of Taxes.

     “ Term Loan Agreement ” means a term loan agreement substantially in the form of Exhibit E

     “ Termination Date ” has the meaning set forth in Section 8.1(a)(ii) .

     “ TPH ” has the meaning set forth in Section 4.23 .

     “ Transfer Requirements ” means any consent, approval, authorization or permit of, or filing with or notification to, any Person which is required to be obtained, made or complied with for or in connection with any sale, assignment or transfer of any System Asset, other than Post Closing Consents, or the Chipeta Interest (or any interest in any of them).

     “ Transferor Guaranty ” means a written unconditional guaranty by AUM that satisfies the requirements of clause (ii) of the definition of Permitted Transfer under the Chipeta LLC Agreement with respect to the transfer of the Chipeta Interest to the Operating Partnership.

     “ Treasury Regulations ” has the meaning set forth in Section 2.5 .

     “ Unit Consideration ” means 351,424 common units of the Partnership.

     “ WES GP ” has the meaning set forth in the preamble.

     “ Western Gas Operating ” has the meaning set forth in the preamble.

     “ WGR ” has the meaning set forth in the preamble.

     “ WGR Holdings ” has the meaning set forth in the preamble.

     “ WGRAH ” has the meaning set forth in the preamble.

     Section 1.2 Rules of Construction .

     (a) All article, section, schedule and exhibit references used in this Agreement are to articles, sections, schedules and exhibits to this Agreement unless otherwise specified. The schedules and exhibits attached to this Agreement constitute a part of this Agreement and are incorporated herein for all purposes.

     (b) If a term is defined as one part of speech (such as a noun), it shall have a corresponding meaning when used as another part of speech (such as a verb). Terms defined in the singular have the corresponding meanings in the plural, and vice versa. Unless the context of this Agreement clearly requires otherwise, words importing the masculine gender shall include the feminine and neutral genders and vice versa. The terms “ includes, ” “ include ” and “ including ” shall be deemed to be followed by the words “ without limitation ”. The words “ hereof, ” “ hereto, ” “ hereby, ” “ herein, ” “ hereunder ” and words of similar import, when used in this Agreement, shall refer to this Agreement as a whole and not to any particular section or article in which such words appear.

     (c) It is the intention of the Parties that every covenant, term and provision of this Agreement shall be construed simply according to its fair meaning and not strictly for or against any Party (not withstanding any rule of law requiring an agreement to be strictly construed against the drafting party), it being understood that the Parties to this Agreement are sophisticated and have had adequate opportunity and means to retain counsel to represent their interests and to otherwise negotiate the provisions of this Agreement.

     (d) The captions in this Agreement are for convenience only and shall not govern or be considered a part of or affect the construction or interpretation of any provision of this Agreement.

     (e) All references to currency herein shall be to, and all payments required hereunder shall be paid in, United States dollars.

     (f) All accounting terms used herein and not expressly defined herein shall have the meanings given to them under GAAP.

     (g) Any event hereunder requiring the payment of cash or cash equivalents on a day that is not a Business Day shall be deferred until the next Business Day without interest.

     (h) Any reference to a statute, regulation or Law shall include any amendment thereof or any successor thereto, and any rules and regulations promulgated thereunder, in each case as existing on the date of this Agreement.

ARTICLE II
CONTRIBUTION; CLOSING

     Section 2.1 Contribution of the System Assets . At the Closing, upon the terms and subject to the conditions set forth in this Agreement, AUM shall contribute, assign, transfer and convey (or cause to be contributed, assigned, transferred and conveyed) to the Operating Partnership, and the Operating Partnership shall accept contribution of, the System Assets pursuant to the System Asset Conveyances and in accordance with Section 2.7 . As used herein, the term “ System Assets ” means the following (but excluding the Excluded Assets):

     (a) The Systems;

     (b) All contracts, agreements, instruments, undertakings or commitments (including intercompany contracts, agreements, instruments, undertakings or commitments), written or oral, by which any System is bound, or that relate to or are otherwise applicable to any System (including exchange agreements, transportation or gathering agreements, connection or interconnect agreements, construction agreements, operating agreements, work orders, purchase orders, service agreements, rental agreements, compression agreements, utility services agreements, non-disturbance agreements for the benefit of the Contributing Parties, fractionation agreements, and agreements for the sale and purchase of oil, gas, casinghead gas or other Hydrocarbons or processing agreements to the extent applicable to any System), including those identified on Schedule 2.1(b) (hereinafter collectively referred to as “ Contracts ”);

     (c) All easements, Permits, licenses, servitudes, rights-of-way, surface leases, fee interests in real property and other surface rights appurtenant to, and used or held for use in connection with any System (including those identified on Schedule 2.1(c) ) (“ Surface Contracts ”);

     (d) All equipment, machinery, tools, supplies, parts, work-in-progress, radios and other communications equipment, leased personal property, fixtures and other tangible personal property and improvements located on any System or used or held for use primarily in connection with the operation of any System, including those identified on Schedule 2.1(d) (“ Equipment ”);

     (e) All claims, causes of action and rights of Contributing Parties under or pursuant to all warranties, representations and guarantees made by suppliers, vendors, manufacturers, subcontractors and contractors or others relating to products sold, or services provided, to the extent used or held for use in connection with or affecting any of the System Assets;

     (f) To the extent owned by AUM, all Hydrocarbon linefill and Hydrocarbons existing within any System from and after the Effective Time;

     (g) All materials and equipment inventory related to or used primarily in connection with the System Assets;

     (h) All (i) accounts, instruments and general intangibles (as such terms are defined in the Uniform Commercial Code of Texas), cash, cash equivalents, notes payable and receivable, accounts payable and receivable, supplier and customer lists, files and correspondence related thereto, bank accounts, savings accounts, safe deposit boxes and the contents of each of the foregoing, certificates of deposit refunds due customers, refunds from suppliers or contractors, prepaid and deferred items (including taxes) attributable to the ownership or operation of the System Assets on or after the Effective Time; and (ii) Liens in favor of Contributing Parties that exist as of the Effective Time, whether choate or inchoate, under any Law or under any of the Contracts (A) arising from the ownership, operation or sale or other disposition of any of the System Assets or (B) arising in favor of Contributing Parties as the operator of certain of the System Assets, but only to the extent a Recipient Party is appointed successor operator; and

     (i) All land files, gas contract files, gas gathering and processing files, land surveys, maps, engineering data and reports, and other books, records, data, files, and accounting records (regardless of whether paper or electronic media), in each case to the extent related primarily to the System Assets, or used or held for use primarily in connection with the maintenance or operation thereof, but excluding (i) computer or communications software of intellectual property (including tapes, codes, data and program documentation and all tangible manifestations and technical information relating thereto), (ii) attorney-client privileged communications and work product of Contributing Parties’ legal counsel, and (iii) reserve studies and evaluations (subject to such exclusions, the “ Records ”); provided , however , that Contributing Parties may retain copies of such Records as Contributing Parties have reasonably determined may be required for litigation, tax, accounting, or auditing purposes, or otherwise necessary to perform such Parties’ obligations under the Omnibus Agreement and the Services and Secondment Agreement, and provide Recipient Parties with the originals thereof.

     Section 2.2 Excluded Assets . Notwithstanding anything to the contrary in this Agreement, the System Assets shall not include, and there are excepted, reserved and excluded from the transactions contemplated hereby, the following (collectively, the “ Excluded Assets ”):

     (a) All corporate, financial, income and franchise Tax and legal records of Contributing Parties that relate primarily to Contributing Parties’ business generally (whether or not relating to the System Assets), and all books, records and files to the extent that the same relate to the Excluded Assets and copies of those records retained by Contributing Parties pursuant to Section 2.1(i) ;

     (b) All geological and geophysical data (including all seismic data, including reprocessed data) and all logs, interpretive data, technical evaluations, technical outputs, reserve estimates and economic estimates;

     (c) All rights to any refund of Taxes in respect of any Taxes for which any Contributing Party is liable for payment or for which Anadarko is required to indemnify the Recipient Parties under Section 9.3 ;

     (d) Those items listed in Schedule 2.2(d) ;

     (e) All trade credits, accounts receivable, notes receivable, and other receivables attributable to the System Assets with respect to any period of time ending prior to the Effective Time;

     (f) All right, title and interest of Contributing Parties in and to vehicles used in connection with the System Assets;

     (g) All rights, titles, claims and interests of Contributing Parties or any Affiliate of a Contributing Party with respect to any period of time prior to the Effective Time (i) to or under any policy or agreement of insurance or any insurance proceeds, except to the extent Recipient Parties assume liability for a Loss for which a Contributing Party is insured, and (ii) to or under any bond or bond proceeds; and

     (h) Any patent, patent application, logo, service mark, copyright, trade name or trademark of or associated with Contributing Parties or any Affiliate of a Contributing Party or any business of a Contributing Party or of any Affiliate of a Contributing Party.

     Section 2.3 Contribution of the Chipeta Interest . At the Closing, upon the terms and subject to the conditions set forth in this Agreement, AUM shall contribute, assign, transfer and convey (or cause to be contributed, assigned, transferred and conveyed) to the Operating Partnership, and the Operating Partnership shall accept contribution of, the Chipeta Interest pursuant to the Chipeta Interest Contribution Agreement and in accordance with Section 2.7 .

     Section 2.4 Consideration . In consideration for the contribution of the System Assets and the contribution of the Chipeta Interest, the Partnership shall (a) distribute to WGR Holdings at Closing the Cash Consideration, (b) issue to WGR Holdings at Closing the Unit Consideration and (c) issue to the General Partner the GP Consideration.

     Section 2.5 Borrowing by the Partnership; Tax Treatment of Cash Consideration . Immediately prior to the Closing, the Partnership shall borrow the Cash Consideration from Anadarko pursuant to the Term Loan Agreement (the “ Partnership Debt ”). The Parties agree that the distribution of the Cash Consideration to WGR Holdings shall qualify as a “debt-financed transfer” under Section 1.707-5(b) of the Treasury Regulations promulgated under the Code (the “ Treasury Regulations ”) and that the entire amount of the Partnership Debt is allocable to, and shall be allocated to, WGR Holdings under Sections 1.752-2 and 1.707-5(b) of the Treasury Regulations. The Parties agree that the distribution of the Cash Consideration will be disclosed in accordance with the requirements of Section 1.707-3(c)(2) of the Treasury Regulations.

     Section 2.6 Purchase Price Adjustments . The amount of the Cash Consideration shall be subject to cash adjustments pursuant to this Section 2.6 . Each payment of an adjustment to the Cash Consideration shall be made at Closing if the adjustment is determined by such date, or otherwise, in the Final Settlement Statement (defined herein). The Parties shall use all commercially reasonable efforts to agree upon the adjustments set forth in this Section 2.6 , and to resolve any differences with respect thereto. Except as provided herein, no adjustments to the Cash Consideration shall be made after delivery of the Final Settlement Statement.

     (a) Preliminary Settlement Statement . Three Business Days before the Closing Date, the Contributing Parties shall deliver to the Recipient Parties a written statement in the form of Schedule 2.6(a) (the “ Preliminary Settlement Statement ”) setting forth the Cash Consideration (showing the elements described in clauses (i) and (ii) of the definition of Cash Consideration), the Unit Consideration and the GP Consideration. The Preliminary Settlement Statement shall also set forth wire transfer instructions for the Closing payments. Payment of the Cash Consideration, the Unit Consideration and the GP Consideration at the Closing shall be based on the Preliminary Settlement Statement.

     (b) Final Settlement Statement . No later than 45 days after the Closing Date and after consultation with the Recipient Parties, the Contributing Parties shall deliver to the Recipient Parties a revised settlement statement setting forth any applicable revisions to the information in the Preliminary Settlement Statement and also showing in reasonable detail the Contributing Parties’ calculation of any payments to be made pursuant to Section 3.4 upon the finalization of the Final Settlement Statement (which payments are not part of or adjustments to the Cash Consideration), as determined in good faith by the Contributing Parties (said revised statement and the calculation thereof shall be referred to as the “ Final Settlement Statement ”).

     (c) Dispute Procedures . The Final Settlement Statement shall become final and binding on the Parties on the 45th day following the date the Final Settlement Statement is received by the Recipient Parties, unless prior to such date the Recipient Parties deliver written notice to the Contributing Parties of their disagreement with the Final Settlement Statement (a “ Settlement Notice ”). Any Settlement Notice shall set forth the Recipient Parties’ proposed changes to the Final Settlement Statement, including an explanation in reasonable detail of the basis on which the Recipient Parties propose such changes. If the Recipient Parties have timely delivered a Settlement Notice,

the Recipient Parties and the Contributing Parties shall use good faith efforts to reach written agreement on the disputed items. If the disputed items have not been resolved by the Recipient Parties and the Contributing Parties by the 30th day following the Contributing Parties’ receipt of a Settlement Notice, any remaining disputed items shall be submitted to one of Deloitte & Touche LLP, Ernst & Young LLP, KPMG LLP or PricewaterhouseCoopers LLP, as mutually agreed upon by the parties (the “ Independent Accountants ”) for resolution within ten Business Days after the end of the foregoing 30-day period. The fees and expenses of the Independent Accountants shall be borne 50% by the Contributing Parties and 50% by the Recipient Parties. The Independent Accountants’ determination of the disputed items shall be final and binding upon the Parties, and the Parties hereby waive any and all rights to dispute such resolution in any manner, including in court, before an arbiter or appeal. The Final Settlement Statement, as modified to reflect disputes resolved as described above, shall become the Final Settlement Statement.

     (d) Payments . If the final calculated amount as set forth in the Final Settlement Statement exceeds the estimated calculated amount as set forth in the Preliminary Settlement Statement, then the Recipient Parties shall pay to the Contributing Parties the amount of such excess. If the final calculated amount as set forth in the Final Settlement Statement is less than the estimated calculated amount as set forth in the Preliminary Settlement Statement, then the Contributing Parties shall pay to the Recipient Parties the amount of such excess. Any payment shall be made within three Business Days of the date the Final Settlement Statement becomes final pursuant to Section 2.6(c) . Any payment received by the Contributing Parties pursuant to this Section 2.6(d) shall be treated, to the extent allowed by Law, as a reimbursement of pre-formation expenditures pursuant to Section 1.707-4(d) of the Treasury Regulations.

     (e) Access to Records . The Parties shall grant to each other full access to the Records and any other relevant records (but only to the extent the Party may do so without breaching any contractual restriction binding on such Party, provided that such Party will use commercially reasonable methods to have such restriction(s) waived for such purpose) and its relevant personnel to allow each of them to make evaluations under this Section 2.6 .

     Section 2.7 Contemplated Legal Steps . To avoid multiple state law conveyances of the System Assets and the Chipeta Interest, each Party entitled to receive an interest in the System Assets and the Chipeta Interest pursuant to this Section 2.7 agrees that AUM is instructed to convey such interests to each successive Party such that AUM will convey legal title to the System Assets and the Chipeta Interest directly to the Operating Partnership in a single state law conveyance, which shall accomplish the following discrete transfers:

     (a) AUM distributes the System Assets and the Chipeta Interest (collectively, the “ Contributed Assets ”) to WGRAH;

     (b) WGRAH distributes the Contributed Assets to WGR;

     (c) WGR contributes the Contributed Assets to WGR Holdings;

     (d) WGR Holdings contributes an undivided interest in the Contributed Assets to the General Partner where:

     (i) The undivided interest transferred by WGR Holdings to the General Partner is equal to 1.98% of “Net Equity”; and

     (ii) “Net Equity” is an amount equal to the gross fair market value of the Contributed Assets minus the Cash Consideration to be distributed to WGR Holdings pursuant to Section 2.4 ;

     (e) WGR Holdings contributes an undivided interest in the Contributed Assets to WES GP equal to 0.02% of Net Equity;

     (f) WES GP contributes an undivided interest in the Contributed Assets to the General Partner equal to 0.02% of Net Equity;

     (g) WGR Holdings and the General Partner contribute their respective undivided interests in the Contributed Assets to the Partnership such that:

     (i) The General Partner receives an increased general partner capital account and the GP Consideration; and

     (ii) WGR Holdings receives the Cash Consideration and the Unit Consideration;

     (h) The Partnership conveys an undivided .01% interest in the Contributed Assets to Western Gas Operating; and

     (i) The Partnership and Western Gas Operating convey their undivided interests in the Contributed Assets to the Operating Partnership in exchange for increased capital accounts.

ARTICLE III
CLOSING

     Section 3.1 The Closing . The closing of the transactions contemplated by this Agreement (the “ Closing ”) shall take place at the offices of Anadarko Petroleum Corporation, 1201 Lake Robbins Drive, The Woodlands, Texas 77380, commencing at 10:00 a.m. local time on the third Business Day following the satisfaction or waiver of all conditions to the obligations of the Parties to consummate the transactions contemplated hereby (other than conditions with respect to actions the Parties shall take at the Closing itself) or such other date as Recipient Parties and Contributing Parties may mutually determine (the “ Closing Date ”), subject to the rights of the Parties under Article VIII ; provided , however , that after the Closing has occurred, unless otherwise agreed by the Parties, the Closing shall be deemed to have been consummated at 12:01 a.m. Houston, Texas time on the Closing Date (the “ Effective Time ”).

     Section 3.2 Deliveries by the Contributing Parties . At the Closing, the Contributing Parties will deliver (or cause to be delivered) the following:

     (a) A counterpart to the Chipeta Interest Contribution Agreement, duly executed by the applicable Contributing Party or Contributing Parties;

     (b) A counterpart to each of the System Asset Conveyances, duly executed by the applicable Contributing Party or Contributing Parties;

     (c) The Contributing Party Closing Certificate, duly executed by an officer of Anadarko;

     (d) A certificate under Section 1.1445-2(b)(2) of the Treasury Regulations certifying that each applicable Contributing Party is not a foreign person within the meaning of Section 1445(f)(3) of the Code;

     (e) A counterpart to the Partnership Agreement Amendment, duly executed by the General Partner;

     (f) A counterpart to the Term Loan Agreement, duly executed by Anadarko;

     (g) A counterpart to the Transferor Guaranty, duly executed by AUM;

     (h) A counterpart to the Omnibus Agreement Amendment, duly executed by Anadarko and the General Partner; and

     (i) Such other certificates, instruments of conveyance and documents as may be reasonably requested by the Recipient Parties prior to the Closing Date to carry out the intent and purposes of this Agreement.

     Section 3.3 Deliveries by the Recipient Parties . At the Closing, the Recipient Parties will deliver (or cause to be delivered) the following:

     (a) The Cash Consideration, by wire transfer to an account specified by WGR;

     (b) The Unit Consideration, by issuance of a certificate reflecting the issuance of such common units to Anadarko or the Anadarko Entity designated by WGR, by instruction to the Partnership’s transfer agent or otherwise;

     (c) The GP Consideration, by issuance of a certificate reflecting the issuance of such general partner units to the General Partner;

     (d) A counterpart to the Chipeta Interest Contribution Agreement, duly executed by the applicable Recipient Party or Recipient Parties;

     (e) A counterpart to each of the System Asset Conveyances, duly executed by the applicable Recipient Party or Recipient Parties;

     (f) The Recipient Party Closing Certificate, duly executed by an officer of the General Partner;

     (g) A counterpart to the Term Loan Agreement, duly executed by the Partnership;

     (h) A counterpart to the Omnibus Agreement Amendment, duly executed by the Partnership; and

     (i) Such other certificates, instruments of conveyance and documents as may be reasonably requested by the Contributing Parties prior to the Closing Date to carry out the intent and purposes of this Agreement.

     Section 3.4 Receipts and Credits .

     (a) Subject to the terms hereof, all monies, proceeds, receipts, credits and income attributable to the System Assets (as determined in accordance with GAAP consistent with past practices) (i) for all periods of time at, from and after 12:01 a.m. Houston, Texas time on the first day of the calendar month in which the Closing occurs (the “ Accounting Time ”), shall be the sole property and entitlement of the Recipient Parties, and, to the extent received by any Contributing Party or one of its Affiliates, shall be promptly accounted for and transmitted to the appropriate Recipient Party and (ii) for all periods of time prior to the Accounting Time, shall be the sole property and entitlement of the Contributing Parties and, to the extent received by any Recipient Party, shall be promptly accounted for and