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Exhibit 10.3  

 
 

VOTING AGREEMENT    
    
    BY AND AMONG    
    
    MARKWEST ENERGY PARTNERS L.P.    
    
    AND    
    
    THE FOX FAMILY HOLDERS    
    
    DATED AS OF SEPTEMBER 5, 2007    

   TABLE OF CONTENTS

	 
	 	 
	 	PAGE

	ARTICLE 1	 	    GENERAL	 	1
	 	1.1	 	Defined Terms	 	1
	ARTICLE 2	 	    VOTING	 	2
	 	2.1	 	Agreement to Vote	 	2
	 	2.2	 	No Inconsistent Agreements	 	3
	 	2.3	 	Proxy	 	3
	ARTICLE 3	 	    REPRESENTATIONS AND WARRANTIES	 	4
	 	3.1	 	Representations and Warranties of the Stockholders	 	4
	 	3.2	 	Representations and Warranties of Energy Partners	 	5
	ARTICLE 4	 	    OTHER COVENANTS	 	5
	 	4.1	 	Prohibition on Transfers, Other Actions	 	5
	 	4.2	 	Stock Dividends, etc	 	5
	 	4.3	 	No Solicitation	 	5
	 	4.4	 	Notice of Acquisitions, Proposals Regarding Prohibited Transactions	 	6
	 	4.5	 	Waiver of Appraisal Rights	 	6
	 	4.6	 	Further Assurances	 	6
	 	4.7	 	Stockholder Capacity	 	6
	 	4.8	 	Registration Rights Agreement	 	7
	ARTICLE 5	 	    MISCELLANEOUS	 	7
	 	5.1	 	Termination	 	7
	 	5.2	 	No Ownership Interest	 	7
	 	5.3	 	Publicity	 	7
	 	5.4	 	Notices	 	7
	 	5.5	 	Interpretation	 	8
	 	5.6	 	Counterparts	 	9
	 	5.7	 	Entire Agreement	 	9
	 	5.8	 	Governing Law; Consent to Jurisdiction; Waiver of Jury Trial	 	9
	 	5.9	 	Amendment; Waiver	 	10
	 	5.10	 	Remedies	 	10
	 	5.11	 	Severability	 	10
	 	5.12	 	Successors and Assigns; Third Party Beneficiaries	 	10

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	 	PAGE

	Affiliate	 	1
	Agreement	 	1
	Beneficial Ownership	 	1
	Beneficially Own	 	2
	Beneficially Owned	 	2
	Common Stock	 	1, 2
	control	 	2
	controlled by	 	2
	Covered Shares	 	2
	Energy Partners	 	1
	Existing Shares	 	1
	Grantees	 	3
	Hydrocarbon	 	1
	Lien	 	2
	Merger Agreement	 	1
	Merger Sub	 	1
	Orders	 	4
	Person	 	2
	Representatives	 	2
	Specified Rights	 	4
	Stockholders	 	1
	Transfer	 	2
	under common control with	 	2

ii

VOTING AGREEMENT  

        VOTING AGREEMENT, dated as of September 5, 2007 (this  "Agreement"), by and
among MARKWEST ENERGY PARTNERS, L.P., a Delaware limited partnership
("Energy Partners"), and JOHN M. FOX AND MWHC HOLDING, INC., a Colorado corporation
(collectively, the "Stockholders" and, individually, "Stockholder"). 

W I T N E S S E T H:  

        WHEREAS, concurrently with the execution of this Agreement, Energy Partners, MarkWest Hydrocarbon, Inc., a
Delaware corporation ("Hydrocarbon") and WMEP, L.L.C., a Delaware limited liability company ("Merger
Sub") are entering into an Agreement and Plan of Merger and Redemption, dated as of the date hereof (as amended, supplemented, restated or otherwise modified from time to time,
the "Merger Agreement") pursuant to which, among other things, Merger Sub will merge with and into Hydrocarbon and each outstanding share of the common
stock, par value $0.01 per share, of Hydrocarbon (the "Common Stock") will be converted into the right to receive the merger consideration specified
therein; 

        WHEREAS, as of the date hereof, each Stockholder is the record and beneficial owner, in the aggregate, of the number of shares of Common
Stock set forth opposite such Stockholder's name on Schedule I hereto (the "Existing Shares"), all of which such shares such Stockholder controls
the right to vote; 

        WHEREAS, as a material inducement to Energy Partners entering into the Merger Agreement, Energy Partners has required that the
Stockholders agree, and the Stockholders have agreed, to enter into this agreement and abide by the covenants and obligations with respect to the Covered Shares (as hereinafter defined) set forth
herein; and 

        WHEREAS, as a material inducement to the Stockholders entering into this Agreement, Energy Partners has agreed to enter into a
Registration Rights Agreement on the Closing Date and grant the Stockholders certain registration rights as provided therein. 

        NOW THEREFORE, in consideration of the foregoing and the mutual representations, warranties, covenants and agreements herein contained,
and intending to be legally bound hereby, the parties hereto agree as follows: 

 
 

ARTICLE 1    
    
    GENERAL    
    

        1.1    Defined Terms.    The following capitalized terms, as used in this Agreement, shall have the meanings set forth
below. Capitalized terms used but not otherwise defined herein shall have the meanings ascribed thereto in the Merger Agreement. 

        "Affiliate" means, with respect to any Person, any other Person that directly, or indirectly through one or more intermediaries, controls,
is controlled by or is under common control with, such specified Person. For purposes of this Agreement, with respect to each Stockholder or other Person, Affiliate shall not include Hydrocarbon or
any Person that is directly or indirectly, through one or more intermediaries, controlled by Hydrocarbon. For the avoidance of doubt, no officer or director of Hydrocarbon, the General Partner, Energy
Partners or any of their controlled Affiliates shall be deemed to be an Affiliate of a Stockholder or other Person by virtue of his, her or its status as a director or officer of Hydrocarbon, the
General Partner, Energy Partners or any of their controlled Affiliates. 

        "Beneficial Ownership" by a Person of any securities includes ownership by any Person who, directly or indirectly, including through any
contract, arrangement, understanding, relationship or otherwise, has or shares (i) voting power which includes the power to vote, or to direct the voting of, such security; and/or
(ii) investment power which includes the power to dispose, or to direct the disposition, of such 

 

security;
and shall otherwise be interpreted in accordance with the term "beneficial ownership" as defined in Rule 13d-3 adopted by the Securities and Exchange Commission under the
Exchange Act; provided that for purposes of determining Beneficial Ownership, a Person shall be deemed to be the Beneficial Owner of any securities which such Person has, at any time during the term
of this Agreement, the right to acquire pursuant to any agreement, arrangement or understanding or upon the exercise of conversion rights, exchange rights, warrants or options, or otherwise
(irrespective of whether the right to acquire such securities is exercisable immediately or only after the passage of time, including the passage of time in excess of 60 days, the satisfaction
of any conditions, the occurrence of any event or any combination of the foregoing). The terms "Beneficially Own" and  "Beneficially Owned"
shall have a correlative meaning. Neither Stockholder shall be deemed to Beneficially Own any of the shares of Common Stock held by
any Person identified on Schedule II hereto (the "Excluded Shares"). 

        "Common Stock" means, the common stock, par value $.01 per share, of Hydrocarbon. 

        "control" (including the terms "controlled by" and "under common
control with"), with respect to the relationship between or among two or more Persons, means the possession, directly or indirectly, of the power to direct or cause the
direction of the affairs or management of a Person, whether through the ownership of voting securities, as trustee or executor, by contract or any other means. 

        "Covered Shares" means, with respect to a Stockholder, such Stockholder's Existing Shares, together with any shares of Common Stock or
other voting capital stock of Hydrocarbon and any securities convertible into or exercisable or exchangeable for shares of Common Stock or other voting capital stock of Hydrocarbon, in each case that
such Stockholder acquires Beneficial Ownership of on or after the date hereof, but shall not include the Excluded Shares. 

        "Lien" means any mortgage, lien, charge, restriction (including restrictions on transfer), pledge, security interest, option, right of
first offer or refusal, preemptive right, put or call option, lease or sublease, claim, right of any third party, covenant, right of way, easement, encroachment or encumbrance. 

        "Person" means any individual, corporation, limited liability company, limited or general partnership, joint venture, association, joint
stock company, trust, unincorporated organization, government or any agency or political subdivision thereof or any other entity, or any group comprised of two or more of the foregoing. 

        "Representatives" means the officers, directors, employees, agents, advisors and Affiliates of a Person. 

        "Transfer" means, directly or indirectly, to sell, transfer, assign, pledge, encumber, hypothecate or similarly dispose of (by merger
(including by conversion into securities or other consideration), by tendering into any tender or exchange offer, by testamentary disposition, by operation of law or otherwise), either voluntarily or
involuntarily, or to enter into any contract, option or other arrangement or understanding with respect to the voting of or sale, transfer, assignment, pledge, encumbrance, hypothecation or similar
disposition of (by merger, by tendering into any tender or exchange offer, by testamentary disposition, by operation of law or otherwise). 

 
 

ARTICLE 2    
    
    VOTING    
    

        2.1    Agreement to Vote.    Each Stockholder hereby irrevocably and unconditionally agrees that during the term of
this Agreement, at the Hydrocarbon Meeting and at any other meeting of the stockholders of Hydrocarbon, however called, including any adjournment or postponement thereof, and 

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in
connection with any written consent of the stockholders of Hydrocarbon, such Stockholder shall, in each case to the fullest extent that the Covered Shares are entitled to vote thereon or consent
thereto: 

        (a)   appear at each such meeting or otherwise cause its Covered Shares to be counted as present thereat for purposes of
calculating a quorum; and 

        (b)   vote (or cause to be voted), in person or by proxy, or deliver (or cause to be delivered) a written consent covering, all
of the Covered Shares (i) in favor of the adoption of the Redemption Charter Amendment, the Merger Agreement and the approval of the Merger and any other action reasonably requested by Energy
Partners in furtherance thereof, submitted for the vote or written consent of stockholders; (ii) against any action or agreement that would result in a breach of any covenant, representation or
warranty or any other obligation or agreement of Hydrocarbon contained in the Merger Agreement; (iii) against any Acquisition Proposal; and (iv) against any action, agreement or
transaction that would impede, interfere with, delay, postpone, discourage, frustrate the purposes of or adversely affect the Merger or the other transactions contemplated by the Merger Agreement. 

        2.2    No Inconsistent Agreements.    Each Stockholder hereby covenants and agrees that, except for this Agreement,
such Stockholder (a) has not entered into, and shall not enter into at any time while this Agreement remains in effect, any voting agreement or voting trust with respect to its Covered Shares,
(b) has not granted, and shall not grant at any time while this Agreement remains in effect, a proxy (except pursuant to Section 2.3 hereof), consent or power of attorney with respect to
its Covered Shares and (c) has not taken and shall not knowingly take any action that would make any representation or warranty of such Stockholder contained herein untrue or incorrect or have
the effect of preventing or disabling such Stockholder from performing any of his or its obligations under this Agreement. Notwithstanding the foregoing and Section 2.3, if a proxy relating to
Hydrocarbon's 2008 annual meeting of stockholders is mailed to Hydrocarbon stockholders prior to the termination of this Agreement, each Stockholder may grant a proxy with respect to the voting of his
or its Covered Shares at such meeting, provided that no matter relating to the Merger or any transaction contemplated in the Merger Agreement is to be considered at such meeting and that such proxy is
not otherwise inconsistent with this Agreement. 

        2.3    Proxy.    In order to secure the obligations set forth herein, Stockholder hereby irrevocably appoints as his
or its proxy and attorney-in-fact, as the case may be Nancy K. Buese and Andy Schroeder, in their respective capacities as officers of Energy Partners or the General Partner,
and any individual who shall hereafter succeed to any such officer of Energy Partners or the General Partner, as the case may be, and any other Person designated in writing by Energy Partners or the
General Partner (collectively, the "Grantees"), each of them individually, with full power of substitution, to vote or execute written consents with
respect to the Covered Shares in accordance with Section 2.1 hereof and, in the discretion of the Grantees, with respect to any proposed postponements or adjournments of any annual or special
meeting of the stockholders of Hydrocarbon at which any of the matters described in Section 2.1(b) are to be considered; provided that any exercise of this proxy by such Grantees shall be
subject to the approval of such exercise by the Conflicts Committee. This proxy is coupled with an interest and shall be irrevocable, except upon termination of this Agreement, and each Stockholder
will take such further action or execute such other instruments as may be necessary to effectuate the intent of this proxy and hereby revokes any proxy previously granted by such Stockholder with
respect to the Covered Shares. Energy Partners may terminate this proxy with respect to any Stockholder at any time at its sole election by written notice provided to such Stockholder. 

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ARTICLE 3    
    
    REPRESENTATIONS AND WARRANTIES    
    

        3.1    Representations and Warranties of the Stockholders.    Each Stockholder (except to the extent otherwise
provided herein) hereby severally but not jointly represents and warrants to Energy Partners as follows: 

        (a)    Organization; Authorization; Validity of Agreement; Necessary
Action.    Stockholder has the requisite power and authority to execute and deliver this Agreement, to carry out his or its obligations hereunder and to consummate
the transactions contemplated hereby. The execution and delivery by Stockholder of this Agreement, the performance by him or it of the obligations hereunder and the consummation of the transactions
contemplated hereby have been duly and validly authorized by Stockholder and no other actions or proceedings on the part of Stockholder to authorize the execution and delivery of this Agreement, the
performance by Stockholder of the obligations hereunder or the consummation of the transactions contemplated hereby. This Agreement has been duly executed and delivered by Stockholder and, assuming
the due authorization, execution and delivery of this Agreement by Energy Partners, constitutes a legal, valid and binding agreement of Stockholder, enforceable against him or it in accordance with
its terms, subject to bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and similar laws of general applicability relating to or affecting creditors' rights and to general
equitable principles. 

        (b)    Ownership.    Stockholder's Existing Shares are, and all of the
Covered Shares owned by Stockholder from the date hereof through and on the Closing Date will be, Beneficially Owned by Stockholder, except to the extent such Covered Shares constitute any warrants,
options, conversion rights or similar rights with respect to Common Stock (collectively, "Specified Rights") that expire after the date hereof.
Stockholder has good and marketable title to Stockholder's Existing Shares, free and clear of any Lien. Except to the extent Covered Shares constitute Specified Rights that expire after the date
hereof and except as set forth on Schedule III, Stockholder has and will have at all times through the Closing Date sole voting power (including the right to control such vote as contemplated
herein), sole power of disposition, sole power to issue instructions with respect to the matters set forth in Article 2 hereof, and sole power to agree to all of the matters set forth in this
Agreement, in each case with respect to all of Stockholder's Existing Shares and with respect to all of the Covered Shares owned by Stockholder at all times through the Closing Date (subject, in the
case of Covered Shares underlying Specified Rights acquired after the date hereof, to the terms of such Specified Rights). 

        (c)    No Violation.    Neither the execution and delivery of this
Agreement by Stockholder nor the performance by Stockholder of his or its obligations under this Agreement will (A) result in a violation or breach of or conflict with any provisions of, or
constitute a default (or an event which, with notice or lapse of time or both, would constitute a default) under, or result in the termination, cancellation of, or give rise to a right of purchase
under, or accelerate the performance required by, or result in a right of termination or acceleration under, or result in the creation of any Lien upon any of the properties, rights or assets,
including but not limited to the Existing Shares, owned or operated by Stockholder, or result in being declared void, voidable, or without further binding effect, or otherwise result in a detriment to
Stockholder under any of the terms, conditions or provisions of any note, bond, mortgage, indenture, deed of trust, license, contract, lease, agreement or other instrument or obligation of any kind to
which Stockholder is a party or by which Stockholder or any of his or its respective properties, rights or assets may be bound (B) violate any judgments, decrees, injunctions, rulings, awards,
settlements, stipulations, orders (collectively, "Orders") or laws applicable to Stockholder or any of his properties, rights or 

4

 

assets
or, in the case of MWHC Holdings, Inc., result in a violation or breach of or conflict with its certificate of incorporation or bylaws. 

        (d)    Consents and Approvals.    No consent, approval, Order or
authorization of, or registration, declaration or filing with, any governmental authority is necessary to be obtained or made by Stockholder in connection with Stockholder's execution, delivery and
performance of this Agreement or the consummation by Stockholder of the transactions contemplated hereby, except (i) for any reports under Sections 13(d) and 16 of the Exchange Act as may be
required in connection with this Agreement and the transactions contemplated hereby. 

        (e)    Absence of Litigation.    There is no action, litigation or
proceeding pending and no Order of any governmental authority outstanding nor, to the knowledge of Stockholder, is any such action, litigation, proceeding or Order threatened, against Stockholder or
the Existing Shares which may prevent or materially delay Stockholder from performing his obligations under this Agreement or consummating the transactions contemplated hereby on a timely basis. 

        (f)    Reliance by Energy Partners.    Stockholder understands and
acknowledges that Energy Partners is entering into the Merger Agreement in reliance upon Stockholder's execution and delivery of this Agreement and the representations and warranties of Stockholder
contained herein. 

        3.2    Representations and Warranties of Energy Partners.    Energy Partners hereby represents and warrants to each
Stockholder that the execution and delivery of this Agreement by Energy Partners and the consummation of the transactions contemplated hereby have been duly authorized by all necessary action on the
part of Energy Partners. 

 
 

ARTICLE 4    
    
    OTHER COVENANTS    
    

        4.1    Prohibition on Transfers, Other Actions.    Stockholder hereby agrees not to (i) Transfer any of the
Covered Shares, Beneficial Ownership thereof or any other interest therein; (ii) enter into any agreement, arrangement or understanding with any Person, or take any other action, that violates
or conflicts with or would reasonably be expected to violate or conflict with, or result in or give rise to a violation of or conflict with, Stockholder's representations, warranties, covenants and
obligations under this Agreement; (iii) take any action that could restrict or otherwise affect Stockholder's legal power, authority and right to comply with and perform his or its covenants
and obligations under this Agreement; or (iv) permit the Covered Shares to become subject to any Lien. Any Transfer in violation of this provision shall be null and void. 

        4.2    Stock Dividends, etc.    In the event of a stock split, stock dividend or distribution, or any change in the
Common Stock by reason of any split-up, reverse stock split, recapitalization, combination, reclassification, exchange of shares or the like, the terms "Existing Shares" and "Covered
Shares" shall be deemed to refer to and include such shares as well as all such stock dividends and distributions and any securities into which or for which any or all of such shares may be changed or
exchanged or which are received in such transaction. 

        4.3    No Solicitation.    Each Stockholder agrees that he or it will not, and shall use his or its reasonable best
efforts to cause his or its Representatives not to, directly or indirectly through another Person, (i) solicit, initiate or knowingly encourage, the submission of any Acquisition Proposal or
the making or consummation thereto, (ii) participate in any discussions or negotiations regarding, or furnish to any person any nonpublic information about Hydrocarbon in connection with, or
otherwise cooperate in any way with, any Acquisition Proposal, (iii) make or participate in, directly or indirectly, a "solicitation" of "proxies" (as such terms are used in the rules of the
U.S. Securities and Exchange 

5

 

Commission)
or powers of attorney or similar rights to vote, or seek to advise or influence any Person with respect to the voting of, any shares of Common Stock in connection with any vote or other
action on any matter, other than to recommend that stockholders of Hydrocarbon vote in favor of the adoption of the Redemption Charter Amendment and the Merger Agreement and as otherwise expressly
provided for in this Agreement, or (iv) agree or publicly propose to do any of the foregoing. Notwithstanding anything to the contrary in this Section 4.3, nothing contained in this
Agreement shall prohibit a Stockholder from furnishing any information to, or entering into or participating in discussions or negotiations with, any person (that is not an Affiliate of such
Stockholder) that makes a written Acquisition Proposal, not in breach of Section 6.6 of he Merger Agreement, pursuant to which such Stockholder would be treated on an equivalent basis with
Hydrocarbon's other holders of Common Stock if (i) the Deal Committee determines that such Acquisition Proposal constitutes or is likely to result in a Superior Proposal and (ii) prior
to Stockholder furnishing such non-public information to such person, Hydrocarbon receives from such person an executed confidentiality agreement no less restrictive than the
Confidentiality Agreement and furnishes Energy Partners with any such information that has not previously been furnished. Each Stockholder hereby represents that, as of the date hereof, such
Stockholder is not engaged in any discussions or negotiations with respect to any Acquisition Proposal and shall use his or its reasonable best efforts to cause such Stockholder's Representatives to
immediately cease and cause to be terminated all existing discussions or negotiations with any Person conducted heretofore with respect to any Acquisition Proposal and request the prompt return or
destruction of all confidential information previously furnished and will take commercially reasonable steps to inform his or its Representatives of the obligations undertaken by such Stockholder
pursuant to this Agreement, including this Section 4.3. 

        4.4    Notice of Acquisitions, Proposals Regarding Prohibited Transactions.    Each Stockholder hereby agrees to
notify Energy Partners as promptly as practicable (and in any event within 24 hours after receipt) of (i) the number of any additional shares of Common Stock or other securities of
Hydrocarbon of which Stockholder acquires Beneficial Ownership on or after the date hereof, and (ii) any inquiries or proposals which are received by, any information which is requested from,
or any negotiations or discussions which are sought to be initiated or continued with, Stockholder or any of his or its Affiliates with respect to any Acquisition Proposal or any other matter referred
to in Section 4.3 (including the material terms thereof and the identity of such person(s) making such inquiry or proposal, requesting such information or seeking to initiate or continue such
negotiations or discussions, as the case may be). Each Stockholder will keep Energy Partners informed on a reasonably current basis of material developments with respect to any such Acquisition
Proposal. 

        4.5    Waiver of Appraisal Rights.    To the fullest extent permitted by applicable law, each Stockholder hereby
agrees not to make a written demand or file a petition for appraisal in respect of its Covered
Shares pursuant to Section 262 of the General Corporation Law of the State of Delaware in connection with the Merger or the Redemption Charter Amendment. 

        4.6    Further Assurances.    From time to time, at Energy Partners' request and without further consideration, each
Stockholder shall execute and deliver such additional documents and take all such further action as may be reasonably necessary or advisable to effect the actions and consummate the transactions
contemplated by this Agreement. 

        4.7    Stockholder Capacity.    Each Stockholder has entered into this Agreement solely in the capacity as a
Beneficial Owner of Covered Shares. Notwithstanding anything to the contrary contained in this Agreement: (i) none of the provisions of this Agreement shall be construed to prohibit, limit or
restrict either Stockholder or any of its Representatives who is an officer or a member of the Board of Directors of Hydrocarbon or Energy Partners from exercising his or its fiduciary duties to
Hydrocarbon or Energy Partners by voting or taking any other action whatsoever in his or her capacity as an officer or director, including with respect to the Merger Agreement and the transactions
contemplated thereby; and (ii) no action taken by Hydrocarbon or Energy Partners in respect of any Acquisition 

6

 

Proposal
shall serve as the basis of a claim that a Stockholder is in breach of its obligations hereunder notwithstanding the fact that such Stockholder or its Representatives have provided advice or
assistance to Hydrocarbon or Energy Partners in connection therewith. 

        4.8    Registration Rights Agreement.    On the Closing Date, each of Energy Partners and the Stockholders shall
execute and deliver the Registration Rights Agreement, in the form attached hereto as Exhibit A pursuant to which Energy Partners will agree to
grant certain registration rights to the Stockholders. 

 
 

ARTICLE 5    
    
    MISCELLANEOUS    
    

        5.1    Termination.    This Agreement shall remain in effect until the earliest to occur of (i) the Effective
Time; (ii) the termination of the Merger Agreement in accordance with its terms; (iii) a Hydrocarbon Change of Recommendation; (iv) the amendment of the Merger Agreement to
decrease the Merger Consideration or otherwise alter the Merger Agreement in a manner adverse to the Stockholders
unless such amendment has been consented to by each Stockholder in writing prior to such amendment; or (v) the written agreement of the Stockholders and Energy Partners to termination of this
Agreement. After the occurrence of such applicable event, this Agreement shall terminate and be of no further force. Nothing in this Section 5.1 and no termination of this Agreement shall
relieve or otherwise limit any party of liability for any breach of this Agreement occurring prior to such termination. 

        5.2    No Ownership Interest.    Nothing contained in this Agreement shall be deemed to vest in Energy Partners any
direct or indirect ownership or incidence of ownership of or with respect to any Covered Shares. All rights, ownership and economic benefit relating to the Covered Shares shall remain vested in and
belong to each Stockholder, and Energy Partners shall have no authority to direct such Stockholder in the voting or disposition of any of the Covered Shares, except as otherwise provided herein. 

        5.3    Publicity.    Each Stockholder hereby permits Energy Partners and Hydrocarbon to include and disclose in the
Registration Statement, the Joint Proxy Statement and in such other schedules, certificates, applications, agreements or documents as such entities reasonably determine to be necessary or appropriate
in connection with the consummation of the Merger and the transaction contemplated in the Merger Agreement such Stockholder's identity and ownership of the Covered Shares and the nature of such
Stockholder's commitments, arrangements and understandings pursuant to this Agreement. 

        5.4    Notices.    All notices and other communications hereunder shall be in writing and shall be deemed given when
delivered personally or by telecopy (upon telephonic confirmation of receipt) or on the first Business Day following the date of dispatch if delivered by a recognized next day courier service. All
notices hereunder shall be delivered as set forth below or pursuant to such other instructions as may be designated in writing by the party to receive such notice: 

If
to Energy Partners, to: 

MarkWest
Energy GP, L.L.C.

Attn: General Counsel

1515 Arapahoe Street

Tower 2, Suite 700

Denver, Colorado 80202

Fax: (303) 290-8769 

7

 

With
copies to: 

Vinson &
Elkins L.L.P.

Attn: Michael J. Swidler

666 Fifth Avenue, 26th Floor

New York, NY 10103

Fax: (212)237-0100 

Andrews
Kurth LLP

Attn: Bill Cooper

1350 I Street, N.W., Suite 1100

Washington, D.C. 20005

Fax: (202) 662-2739 

If
to Hydrocarbon, to: 

MarkWest
Hydrocarbon, Inc.

Attn: General Counsel

1515 Arapahoe Street

Tower 2, Suite 700

Denver, Colorado 80202

Fax: (303) 290-8769 

With
copies to: 

Hogan &
Hartson L.L.P.

Attn: George Hagerty

One Tabor Center, Suite 1500

1200 Seventeenth Street

Denver, Colorado 80202

Fax: (303) 899-7333 

Akin,
Gump, Strauss, Hauer & Feld LLP

Attn: Michael E. Dillard, P.C.

1111 Louisiana Street, 44th Floor

Houston, Texas 77002

Fax: (713) 236-0832 

If
to a Stockholder, to: 

MWHC
Holding, Inc.

Attn: John Fox

155 Inverness Drive West, #330

Englewood, Colorado 80112

Fax: (303) 649-2138 

With
copies to: 

Cooley
Godward Kronish LLP

Attn: Francis R. Wheeler, Esq.

380 Interlocken Crescent, Suite 900

Broomfield, Colorado 80021

Fax: (720) 566-4499 

        5.5    Interpretation.    The words "hereof," "herein" and "hereunder" and words of similar import when used in this
Agreement shall refer to this Agreement as a whole and not to any particular provision of this Agreement, and Section references are to this Agreement unless otherwise specified. 

8

 

Whenever
the words "include," "includes" or "including" are used in this Agreement, they shall be deemed to be followed by the words "without limitation." The meanings given to terms defined herein
shall be equally applicable to both the singular and plural forms of such terms. The table of contents and headings contained in this Agreement are for reference purposes only and shall not affect in
any way the meaning or interpretation of this Agreement. This Agreement is the product of negotiation by the parties having the assistance of counsel and other advisers. It is the intention of the
parties that this Agreement not be construed more strictly with regard to one party than with regard to the others. 

        5.6    Counterparts.    This Agreement may be executed by facsimile and in counterparts, all of which shall be
considered one and the same agreement and shall become effective when counterparts have been signed by each of the parties and delivered to the other parties, it being understood that all parties need
not sign the same counterpart. 

        5.7    Entire Agreement.    This Agreement and, solely to the extent of the defined terms referenced herein, the
Merger Agreement, together with the schedule annexed hereto, embody the complete agreement and understanding among the parties hereto with respect to the subject matter hereof and supersede and
preempt any prior understandings, agreements or representations by or among the parties, written and oral, that may have related to the subject matter hereof in any way. 

        5.8    Governing Law; Consent to Jurisdiction; Waiver of Jury Trial.    

        (a)   This Agreement shall be governed by and construed in accordance with the laws of the State of Delaware, regardless of the
laws that might otherwise govern under applicable principles of conflicts of laws thereof. The parties agree that irreparable damage would occur and that the parties would not have any adequate remedy
at law in the event that any of the provisions of this Agreement were not performed in accordance with their specific terms or were otherwise breached. It is accordingly agreed that the parties shall
be entitled to an injunction or injunctions to prevent breaches of this Agreement and to enforce specifically the terms and provisions of this Agreement in the Court of Chancery of the State of
Delaware (and any appellate court of the State of Delaware) and the Federal courts of the United States of America located in the State of Delaware, this being in addition to any other remedy to which
they are entitled at law or in equity. In addition, each of the parties hereto (i) consents to submit itself to the personal jurisdiction of the Court of Chancery of the State of Delaware (and
any appellate court of the State of Delaware) and the Federal courts of the United States of America located in the State of Delaware in the event any dispute arises out of this Agreement or the
transactions contemplated by this Agreement, (ii) agrees that it will not attempt to deny or defeat such personal jurisdiction by motion or other request for leave from any such court and
(iii) agrees that it will not bring any action relating to this Agreement or the transactions contemplated by this Agreement in any court other than the Court of Chancery of the State of
Delaware or a Federal court of the United States of America located in the State of Delaware. 

        (b)   EACH PARTY HERETO HEREBY WAIVES, TO THE FULLEST EXTENT PERMITTED BY APPLICABLE LAW, ANY RIGHT IT MAY HAVE TO A TRIAL BY
JURY IN RESPECT OF ANY SUIT, ACTION OR OTHER PROCEEDING ARISING OUT OF THIS AGREEMENT OR THE TRANSACTIONS CONTEMPLATED HEREBY. EACH PARTY HERETO (A) CERTIFIES THAT NO REPRESENTATIVE, AGENT OR
ATTORNEY OF ANY OTHER PARTY HAS REPRESENTED, EXPRESSLY OR OTHERWISE, THAT SUCH PARTY WOULD NOT, IN THE EVENT OF ANY ACTION, SUIT OR PROCEEDING, SEEK TO ENFORCE THE FOREGOING WAIVER AND
(B) ACKNOWLEDGES THAT IT AND THE OTHER PARTIES HERETO HAVE BEEN INDUCED TO ENTER INTO THIS AGREEMENT, BY, AMONG OTHER THINGS, THE MUTUAL WAIVER AND CERTIFICATIONS IN THIS SECTION 5.9. 

9

 

        5.9    Amendment; Waiver.    This Agreement may not be amended except by an instrument in writing signed by Energy
Partners and each Stockholder. Each party may waive any right of such party hereunder by an instrument in writing signed by such party and delivered to Energy Partners and the Stockholders. No
amendment or waiver shall be effective unless, (a) in the case of Energy Partners, the Conflicts Committee shall have approved such amendment or waiver, and (b) the Deal Committee, on
behalf of Hydrocarbon, shall have given its written consent, such consent not to be unreasonably withheld. 

        5.10    Remedies.    

        (a)   Each party hereto acknowledges that monetary damages would not be an adequate remedy in the event that any covenant or
agreement in this Agreement is not performed in accordance with its terms, and it is therefore agreed that, in addition to and without limiting any other remedy or right it may have, the
non-breaching party will have the right to an injunction, temporary restraining order or other equitable relief in any court of competent jurisdiction enjoining any such breach and
enforcing specifically the terms and provisions hereof. Each party hereto agrees not to oppose the granting of such relief in the event a court determines that such a breach has occurred, and to waive
any requirement for the securing or posting of any bond in connection with such remedy. 

        (b)   All rights, powers and remedies provided under this Agreement or otherwise available in respect hereof at law or in
equity shall be cumulative and not alternative, and the exercise or beginning of the exercise of any thereof by any party shall not preclude the simultaneous or later exercise of any other such right,
power or remedy by such party. 

        5.11    Severability.    Any term or provision of this Agreement which is determined by a court of competent
jurisdiction to be invalid or unenforceable in any jurisdiction shall, as to that jurisdiction, be ineffective to the extent of such invalidity or unenforceability without rendering invalid or
unenforceable the remaining terms and provisions of this Agreement or affecting the validity or enforceability of any of the terms or provisions of this Agreement in any other jurisdiction, and if any
provision of this Agreement is determined to be so broad as to be unenforceable, the provision shall be interpreted to be only so broad as is enforceable, in all cases so long as neither the economic
nor legal substance of the transactions contemplated hereby is affected in any manner adverse to any party or its equityholders. Upon any such determination, the parties shall negotiate in good faith
in an effort to agree upon a suitable and equitable substitute provision to effect the original intent of the parties as closely as possible and to the end that the transactions contemplated hereby
shall be fulfilled to the maximum extent possible. 

        5.12    Successors and Assigns; Third Party Beneficiaries.    Neither this Agreement nor any of the rights or
obligations of any party under this Agreement shall be assigned, in whole or in part (by operation of law or otherwise), by any party without the prior written consent of the other parties hereto.
Subject to the foregoing, this Agreement shall bind and inure to the benefit of and be enforceable by the parties hereto and their respective successors and permitted assigns. Nothing in this
Agreement, express or implied, is intended to confer on any Person other than (a) the parties hereto, (b) Hydrocarbon, solely to the extent specified in the next succeeding sentence, or
(c) the parties respective successors and permitted assigns any rights, remedies, obligations or liabilities under or by reason of this Agreement. The parties hereto agree that Hydrocarbon
shall be an intended third party beneficiary of this Agreement solely to the extent of its right to consent to amendments to or waivers under this Agreement as specified in Section 5.9. 

[Remainder
of this page intentionally left blank] 

10

        IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be signed (where applicable, by their respective officers or other
authorized Person thereunto duly authorized) as of the date first written above. 

	 	 	MARKWEST ENERGY PARTNERS, L.P.:
	

 	
 	

BY:	
 	

MARKWEST ENERGY GP, L.L.C.,

its General Partner
	

 	
 	

By:	
 	

 
	

 	
 	

/s/  NANCY K. BUESE      
 Name
	

 	
 	

Chief Financial Officer
 Title
	

 	
 	
STOCKHOLDERS:
	

 	
 	

/s/  JOHN M. FOX      
 John M. Fox
	

 	
 	
MWHC HOLDINGS, INC.
	

 	
 	

By:	
 	

 
	

 	
 	

/s/  JOHN M. FOX      
 John M. Fox
	

 	
 	

 Title

 
 

Schedule I    
    

 
  STOCKHOLDER INFORMATION    
    

	Name
 
	 	Existing Shares Beneficially Owned

	MWHC Holding, Inc.(1)	 	4,842,387
	

John M. Fox	
 	

at least 331,852

	(1)
	Shares
Beneficially Owned by MWHC Holding, Inc. are also Beneficially Owned by John M. Fox. 

 
 

Schedule II    
    

 
  EXCLUDED SHARES    
    

	Name
 
	 	Excluded Shares Beneficially Owned

	Fox Family Foundation	 	118,000
	

Bode Blanco, L.L.C.	
 	

1,452
	

Brian T. Crabtree Trust	
 	

81,250
	

MaggieGeorge Foundation	
 	

121,035

 
 

Schedule III    
    

 
  EXCEPTIONS TO SOLE BENEFICIAL OWNERSHIP    
    

        Of the at least 331,852 Existing Shares Beneficially Owned by John M. Fox, an aggregate of at least 231,830 are owned as joint tenants with his wife, Marcella F.
Fox. 

 
 

EXHIBIT A    
    
    REGISTRATION RIGHTS AGREEMENT

QuickLinks

VOTING AGREEMENT BY AND AMONG MARKWEST ENERGY PARTNERS L.P. AND THE FOX FAMILY HOLDERS DATED AS OF SEPTEMBER 5, 2007

ARTICLE 1 GENERAL

ARTICLE 2 VOTING

ARTICLE 3 REPRESENTATIONS AND WARRANTIES

ARTICLE 4 OTHER COVENANTS

ARTICLE 5 MISCELLANEOUS

Schedule I

STOCKHOLDER INFORMATION

Schedule II

EXCLUDED SHARES

Schedule III

EXCEPTIONS TO SOLE BENEFICIAL OWNERSHIP

EXHIBIT A REGISTRATION RIGHTS AGREEMENTQuickLinks
 -- Click here to rapidly navigate through this document

Exhibit 10.4  

 
 

CLASS B MEMBERSHIP INTEREST
  CONTRIBUTION AGREEMENT
  
  
  dated as of
  
  
  September 5, 2007
  
  
  by and among
  
  
  MARKWEST ENERGY PARTNERS, L.P.,
  
  

and
  
  
  THE SELLERS NAMED HEREIN    
    

  

 
 

Table of Contents    
    

	 
	 	 
	 	Page

	

ARTICLE I

DEFINITIONS
	

Section 1.1	
 	

Definitions	
 	

1
	Section 1.2	 	Rules of Construction	 	4
	

ARTICLE II

CONTRIBUTION OF CLASS B INTERESTS; CLOSING
	

Section 2.1	
 	

Contribution of Class B Interests	
 	

4
	Section 2.2	 	Closing	 	4
	Section 2.3	 	Sellers' Closing Deliveries	 	4
	Section 2.4	 	Buyer's Closing Deliveries	 	5
	

ARTICLE III

REPRESENTATIONS AND WARRANTIES
	

Section 3.1	
 	

Representations of the Sellers	
 	

5
	Section 3.2	 	Representations of Buyer	 	7
	

ARTICLE IV

ADDITIONAL AGREEMENTS, COVENANTS, RIGHTS AND OBLIGATIONS
	

Section 4.1	
 	

Commercially Reasonable Best Efforts; Further Assurances	
 	

9
	Section 4.2	 	Registration Rights Agreement	 	9
	Section 4.3	 	No Solicitation	 	9
	Section 4.4	 	Expenses	 	10
	Section 4.5	 	Public Announcements	 	10
	Section 4.6	 	Reimbursement for Certain Contributions to the Company	 	10
	Section 4.7	 	Seller Capacity	 	10
	Section 4.8	 	Distributions	 	10
	Section 4.9	 	Legends	 	10
	

ARTICLE V

CLOSING CONDITIONS
	

Section 5.1	
 	

Mutual Conditions	
 	

11
	Section 5.2	 	Buyer's Conditions	 	11
	Section 5.3	 	Sellers' Conditions	 	11
	

ARTICLE VI

TERMINATION
	

Section 6.1	
 	

Termination	
 	

12
	Section 6.2	 	Effect of Termination	 	12
	

ARTICLE VII

INDEMNIFICATION
	

Section 7.1	
 	

Seller's Indemnity	
 	

13
	Section 7.2	 	Survival	 	13
	Section 7.3	 	Enforcement of this Agreement	 	13
	Section 7.4	 	No Waiver Relating to Claims for Fraud or Willful Misconduct	 	13
	 	 	 	 	 

i

 

	

ARTICLE VIII

MISCELLANEOUS
	

Section 8.1	
 	

Notices	
 	

13
	Section 8.2	 	Waiver and Amendment; Entire Agreement	 	14
	Section 8.3	 	Binding Effect and Assignment	 	15
	Section 8.4	 	Severability	 	15
	Section 8.5	 	Headings	 	15
	Section 8.6	 	Governing Law; Jurisdiction	 	15
	Section 8.7	 	Waiver of Jury Trial	 	16
	Section 8.8	 	Negotiated Agreement	 	16
	Section 8.9	 	Counterparts	 	16
	Section 8.10	 	No Act or Failure to Act	 	16

EXHIBITS  

	Exhibit A	 	—	 	Form of Bill of Sale for Class B Membership Interest
	Exhibit B	 	—	 	Form of Seller's Closing Certificate
	Exhibit C	 	—	 	Form of FIRPTA Certificate
	Exhibit D	 	—	 	Form of Buyer's Closing Certificate
	Exhibit E	 	—	 	Form of Registration Rights Agreement

ii

CONTRIBUTION AGREEMENT  

        THIS CLASS B MEMBERSHIP INTEREST CONTRIBUTION AGREEMENT, dated as of September 5, 2007 (this
"Agreement"), is entered into by and among each of the Sellers listed in Schedule 2.1 attached
hereto (each referred to herein as a "Seller" and collectively, the "Sellers"), and MarkWest Energy
Partners, L.P., a Delaware limited partnership ("Buyer"). The Sellers and the Buyer are collectively referred to herein as the
"Parties," with each a "Party." 

WITNESSETH:  

        WHEREAS, MarkWest Hydrocarbon, Inc., a Delaware corporation ("Hydrocarbon"), owns all of the outstanding
Class A Membership Interests (as defined) in MarkWest Energy GP LLC, a Delaware limited liability company (the "Company"), representing a 89.7%
Membership Interest (as defined) in the Company, and the Sellers collectively own all of the outstanding Class B Membership Interests (as defined) in the Company, representing, in the
aggregate, a 10.3% Membership Interest in the Company, with each Seller owning the Class B Membership Interest specified on Schedule 2.1
attached hereto; 

        WHEREAS,
subject to the terms and conditions set forth herein, each of the Sellers desires to contribute to Buyer, and Buyer desires for the Seller to contribute to it, their respective
Class B Membership Interests in exchange for cash and common units representing limited partnership interests in the Buyer ("Common Units"); 

        WHEREAS,
as a material inducement to the Sellers entering into this Agreement, the Buyer has agreed to enter into a Registration Rights Agreement on the Closing Date and grant the
Sellers certain registration rights as provided therein; 

        WHEREAS,
as of the date hereof, pursuant to the requirements of Section 12.1 of the Company LLC Act, in its capacity as the Class A Member of the Company, Hydrocarbon has
consented to the transactions contemplated by this Agreement; and 

        WHEREAS,
on the date hereof, the Buyer, Hydrocarbon and MWEP, L.L.C. ("MergerCo") have entered into an Agreement and Plan of Redemption
and Merger (the "Merger Agreement"), pursuant to which (i) Hydrocarbon will redeem a portion of its outstanding shares of common stock (the
"Redemption") and then (ii) MergerCo will merge (the "Merger") with and into Hydrocarbon, with
Hydrocarbon surviving, such that following the Redemption and Merger, Hydrocarbon will be a direct, wholly owned subsidiary of the Buyer. 

        NOW,
THEREFORE, in consideration of the mutual covenants, representations, warranties and agreements contained herein, and intending to be legally bound hereby, the parties hereto agree
as follow: 

ARTICLE I

DEFINITIONS  

        Section 1.1    Definitions.    In this Agreement, unless the context otherwise
requires, the following terms shall have the following meanings respectively: 

        "Affiliate," when used with respect to a Person, means any other Person that directly or indirectly controls, is controlled by or is under
common control with such first Person. 

        "Aggregate Consideration Value," with respect to a Seller, means the sum of (i) the cash received by such Seller pursuant to this
Agreement plus (ii) the product of (A) the number of Common Units received by such Seller pursuant to this Agreement multiplied by (B) the Common Unit Price. 

        "Agreement" has the meaning set forth in the Preamble. 

        "Business Day" means any day on which commercial banks are generally open for business in Denver, Colorado other than a Saturday, a Sunday
or a day observed as a holiday in Denver, Colorado under the Laws of the State of Colorado or the federal Laws of the United States of America. 

 

        "Buyer" has the meaning set forth in the Preamble. 

        "Buyer Disclosure Schedule" means the disclosure schedule prepared by Buyer and delivered to Seller as of the date of this Agreement. 

        "Closing" has the meaning set forth in Section 2.2. 

        "Closing Date" has the meaning set forth in Section 2.2. 

        "Class A Membership Interests" has the meaning assigned to such term in the Company LLC Agreement. 

        "Class B Membership Interests" has the meaning assigned to such term in the Company LLC Agreement. 

        "Code" means the Internal Revenue Code of 1986, as amended. 

        "Common Unit Price" means $33.32. 

        "Common Units" has the meaning set forth in the recitals. 

        "Company" has the meaning set forth in the recitals. 

        "Company LLC Agreement" means the Amended and Restated Limited Liability Company Agreement of the Company, dated May 24, 2002, as
amended by Amendment No. 1 thereto, dated effective December 31, 2004, and Amendment No. 2 thereto, dated effective January 19, 2005. 

        "Conflicts Committee" means the Conflicts Committee of the Board of Directors of the Company. 

        "control," and its derivatives, means the possession, directly or indirectly, of the power to direct or cause the direction of the
management and policies of a Person. 

        "Delaware LLC Act" means Delaware Revised Limited Liability Company Act. 

        "Encumbrances" means pledges, restrictions on transfer, proxies and voting or other agreements, liens, claims, charges, mortgages,
security interests or other legal or equitable encumbrances, limitations or restrictions of any nature whatsoever. 

        "Exchange Act" means the Securities Exchange Act of 1934, as amended. 

        "FIRPTA" means the Foreign Investment in Real Property Tax Act. 

        "Fox Support Agreement" means the Voting Agreement, dated the date hereof, among the Buyer and the Stockholders (as defined therein). 

        "GAAP" means United States generally accepted accounting principles applied on a consistent basis during the periods involved. 

        "governing documents" means, with respect to any person, the certificate or articles of incorporation, by-laws, articles of
organization, limited liability company agreement, partnership agreement, formation agreement, joint venture agreement, operating agreement, unanimous equityholder agreement or declaration or other
similar governing documents of such person. 

        "Governmental Authority" means any (a) multinational, federal, national, provincial, territorial, state, regional, municipal, local
or other government, governmental or public department, central bank, court, tribunal, arbitral body, commission, administrative agency, board, bureau or agency, domestic or foreign,
(b) subdivision, agent, commission, board, or authority of any of the foregoing, or (c) quasi-governmental or private body exercising any regulatory, expropriation or taxing authority
under, or for the account of, any of the foregoing, in each case which has jurisdiction or authority with respect to the applicable party. 

2

 

        "Indemnified Parties" has the meaning set forth in Section 7.1. 

        "IDRs" means the Incentive Distribution Rights (as such term in defined in the Partnership Agreement). 

        "Laws" means all statutes, regulations, statutory rules, orders, judgments, decrees and terms and conditions of any grant of approval,
permission, authority, permit or license of any court, Governmental Authority, statutory body or self-regulatory authority (including the NYSE). 

        "Material Adverse Effect" means, with respect to Buyer, any effect that (i) is material and adverse to the financial position,
results of operations, business, assets or prospects of Buyer and its Subsidiaries taken as a whole or (ii) would materially impair the ability of Buyer to perform its obligations under this
Agreement or otherwise materially threaten or materially impede the consummation of the transactions contemplated by this Agreement. 

        "Membership Interests" has the meaning assigned to such term in the Company LLC Agreement. 

        "Merger" has the meaning set forth in the recitals. 

        "Merger Agreement" has the meaning set forth in the recitals. 

        "NYSE" means the New York Stock Exchange. 

        "Order" means any judgment, decree, injunction, ruling, award, settlement, stipulation or orders of a Governmental Authority. 

        "Partnership Agreement" means the Amended and Restated Agreement of Limited Partnership of Buyer. 

        "Person" or "person" means any individual, corporation, limited liability company, limited
or general partnership, joint venture, association, joint stock company, trust, unincorporated organization, government or any agency or political subdivision thereof or any other entity, or any group
comprised of two or more of the foregoing. 

        "Previously Disclosed" by a party shall mean information set forth in its Disclosure Schedule. 

        "Registration Statement" has the meaning set forth in Section 4.2. 

        "Representatives" means with respect to a Person, its directors, officers, employees, agents and representatives, including any investment
banker, financial advisor, attorney, accountant or other advisor, agent or representative. 

        "Rights" shall mean, with respect to any person, securities or obligations convertible into or exchangeable for, or giving any person any
right to subscribe for or acquire, or any options, calls or commitments relating to, equity securities of such person. 

        "Securities Act" means the Securities Act of 1933, as amended. 

        "Seller" has the meaning set forth in the Preamble. 

        "Seller Disclosure Schedule" means the disclosure schedule prepared each Seller and delivered to Buyer as of the date of this Agreement. 

        "Subsidiary" shall mean an Affiliate of a Person that is controlled by such Person directly, or indirectly through one or more
intermediaries. 

        "Tax" or "Taxes" shall mean any and all taxes, including any interest, penalties or other
additions to tax that may become payable in respect thereof, imposed by any federal, state, local or foreign government or any agency or political subdivision of any such government, which taxes shall
include, without limiting the generality of the foregoing, all income or profits taxes, payroll and employee 

3

 

withholding
taxes, unemployment insurance taxes, social security taxes, severance taxes, license charges, taxes on stock, sales and use taxes, ad valorem taxes, excise taxes, franchise taxes, gross
receipts taxes, business license taxes, occupation taxes, real and personal property taxes, stamp taxes, environmental taxes, transfer taxes, workers' compensation and other obligations of the same or
of a similar nature to any of the foregoing. 

        "Unaffiliated Common Unitholders" means holders of Common Units other than Hydrocarbon or holders affiliated with Hydrocarbon or the
Company. 

        Section 1.2    Rules of Construction.    In constructing this Agreement: (a) the
word "includes" and its derivatives means "includes, without limitation" and corresponding derivative expressions; (b) the currency amounts referred to herein, unless otherwise specified, are
in United States dollars; (c) whenever this Agreement refers to a number of days, such number shall refer to calendar days unless business days are specified; (d) unless otherwise
specified, all references in this Agreement to "Article," "Section," "Disclosure Schedule," "Exhibit," "preamble" or "recitals" shall be references to an Article, Section, Disclosure Schedule,
Exhibit, preamble or recitals hereto; and (e) whenever the context requires, the words used in this Agreement shall include the masculine, feminine and neuter and singular and the plural. 

ARTICLE II

CONTRIBUTION OF CLASS B INTERESTS; CLOSING  

        Section 2.1    Contribution of Class B Interests.    Upon the terms and subject
to the conditions set forth in this Agreement, at the Closing (as defined below), each Seller agrees, severally and not jointly, to contribute to the Buyer the Class B Membership Interest
specified on Schedule 2.1 attached hereto as owned by such Seller, and the Buyer agrees to accept the contribution of each such Class B
Membership Interest from each Seller and (a) pay to each Seller the amount in cash and (b) issue to each Seller the number of Common Units, in each case, set forth opposite the name of
such Seller on Schedule 2.1 attached hereto. 

        Section 2.2    Closing.    The closing of the sale and purchase and contribution of the
Class B Membership Interests pursuant to this Agreement (the "Closing") shall take place concurrently with the closing of the Merger, subject to
satisfaction or waiver of all of the conditions to each of the respective Parties' obligations to consummate the sale and purchase of the Class B Membership Interest hereunder (such date, the
"Closing Date"); provided, that the Buyer shall have given the Sellers three (3) Business Days
(or such shorter period as shall be agreeable to the Parties) prior written notice of such designated Closing Date. The Closing shall take place at the offices of Hogan & Hartson LLP,
1200 Seventeenth Street, Suite 1500, Denver, Colorado 80202. 

        Section 2.3    Sellers' Closing Deliveries.    At the Closing, each of the Sellers
shall deliver, or cause to be delivered, to the Buyer the following: 

        (a)   a
duly executed assignment and bill of sale in substantially the form attached hereto as Exhibit A, transferring
the Class B Membership Interest of such Seller; 

        (b)   a
closing certificate, substantially in the form attached as Exhibit B, duly executed by, or on behalf of, such
Seller; 

        (c)   a
FIRPTA certificate, in the form attached hereto as Exhibit C duly executed by, or on behalf of, such Seller
(i) stating that such Seller is not a foreign individual, foreign corporation, foreign partnership, foreign trust or foreign estate, (ii) providing such Seller's U.S. Employer
Identification Number and (iii) providing such Seller's address. 

        (d)   the
Registration Rights Agreement, in the form attached hereto as Exhibit E duly executed by, or on behalf of,
such Seller. 

4

 

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

        Section 2.4    Buyer's Closing Deliveries.    At the Closing, Buyer shall deliver, or
cause to be delivered, to each of the Sellers the following: 

        (a)   the
full amount in cash set forth opposite the name of such Seller of Schedule 2.1 by wire transfer of immediately
available funds to the respective accounts designated in writing by such Seller at least two (2) Business Days prior to Closing; 

        (b)   a
duly executed certificate, countersigned by the appropriate officer(s) of the Company, representing the number of Common Units set forth opposite the name of such
Seller on Schedule 2.1 hereto; 

        (c)   such
a closing certificate, substantially in the form attached as Exhibit D, duly executed by, or on behalf of,
Buyer; 

        (d)   the
Registration Rights Agreement, in the form attached hereto as Exhibit E duly executed by, or on behalf of,
Buyer. 

        (e)   a
long-form certificate of good standing of recent date of Buyer; and 

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

ARTICLE III

REPRESENTATIONS AND WARRANTIES  

        Section 3.1    Representations of the Sellers.    Except as set forth in a section of
the Sellers' Disclosure Schedule delivered concurrently herewith corresponding to the applicable sections of this Section 3.1 to which such
disclosure applies, each Seller hereby represents and warrants, severally and not jointly, to Buyer that: 

        (a)    Organization; Authorization; Validity of Agreement; Necessary Action.    This Agreement has been duly executed
and delivered by such Seller and constitutes a legal, valid and binding agreement of such Seller, enforceable against him or it in accordance with its terms, subject to bankruptcy, insolvency,
fraudulent transfer, reorganization, moratorium and similar laws of general applicability relating to or affecting creditors' rights and to general equitable principles. 

        (b)    Ownership.    Such Seller's Class B Membership Interest is, and on the Closing Date will be, owned
beneficially and of record by such Seller and, to the best knowledge of such Seller, has been duly authorized and is validly issued, fully paid (to the extent required under the Company LLC Agreement)
and non-assessable (except as provided under the Delaware LLC Act or the Company LLC Agreement). Such Seller has good and marketable title to such Seller's Class B Membership
Interest, free and clear of any Encumbrances, including any liens for Taxes. Such Seller has and will have at all times through the Closing Date sole voting power, sole power of disposition and sole
power to agree to all of the matters set forth in this Agreement, in each case with respect to such Seller's Class B Membership Interest at all times through the Closing Date. 

        (c)    No Violation.    Neither the execution and delivery of this Agreement by such Seller, the performance by such
Seller of his or its obligations under this Agreement, nor the consummation by such Seller of the transactions contemplated hereby nor compliance by such Seller with any of the provisions herein will
(i) result in the creation of any Encumbrance upon the Class B 

5

 

Membership
Interest or (ii) violate any Orders or Laws applicable to such Seller or any of his properties, rights or assets. 

        (d)    Consents and Approvals.    No consent, approval, Order or authorization of, or registration, declaration or
filing with, any Governmental Authority is necessary to be obtained or made by such Seller in connection with such Seller's execution, delivery and performance of this Agreement or the consummation by
such Seller of the transactions contemplated by this Agreement. 

        (e)    Absence of Litigation.    There is no action, litigation or proceeding pending and no Order of any Governmental
Authority outstanding nor, to the knowledge of such Seller, is any such action, litigation, proceeding or Order threatened, against such Seller or its Class B Membership Interest which may
prevent or materially delay such Seller from performing his obligations under this Agreement or consummating the transactions contemplated hereby on a timely basis. 

        (f)    Brokerage and Finder's Fee.    No fees or commissions will be payable by such Seller to any broker, finder, or
investment banker with respect to the sale of any of such Seller's Class B Membership Interest or the consummation of the transactions contemplated by this Agreement. 

        (g)    No Side Agreements.    Except for this Agreement, the Merger Agreement and the agreements contemplated by the
Merger Agreement, there are no other agreements by, among or between such Seller or any of its Affiliates, on the other hand, and the Company or its Affiliates, on the other hand, with respect to the
transactions contemplated hereby. 

        (h)    Community Property.    Each Seller is a natural person. Except in the case of Jan Kindrick and Kevin Kubat,
each Seller is domiciled and residing in the State of Colorado, and such Seller's Class B Membership Interest is not subject to community property rights. Kevin Kubat is domiciled and residing
in the State of Oklahoma and such Seller's Class B Membership Interest is not subject to community property rights. Jan Kindrick is domiciled and residing in the State of Texas and such
Seller's Class B Membership Interest may be subject to community property rights. 

        (i)    Investment Intent; Investment Experience; Restricted Securities.    In acquiring the Common Units hereunder,
such Seller is not offering or selling, and shall not offer or sell the Common Units, in connection with any distribution of any of such Common Units, and such Seller shall not participate in
any such undertaking or in any underwriting of such an undertaking, except in compliance with applicable federal and state securities Laws. Such Seller acknowledges that it can bear the economic risk
of its investment in the Common Units, and has such knowledge and experience in financial and business matters that it is capable of evaluating the merits and risks of an investment in the Common
Units. Such Seller is an "accredited investor" as such term is defined in Regulation D under the Securities Act. Such Seller understands that none of the Common Units received pursuant to this
Agreement shall have been registered pursuant to the Securities Act or any applicable state securities Laws, that all of such Common Units shall be characterized as "restricted securities" under
federal securities Laws and that under such Laws and applicable regulations none of such Common Units can be sold or otherwise disposed of without registration under the Securities Act or an exemption
therefrom. 

        (j)    Limitation of Representations and Warranties.    EXCEPT FOR THE REPRESENTATIONS AND WARRANTIES SET FORTH IN
THIS SECTION 3.1, SUCH SELLER IS NOT MAKING ANY OTHER REPRESENTATIONS OR WARRANTIES, WRITTEN OR ORAL, STATUTORY, EXPRESS OR IMPLIED. 

6

  

        Section 3.2    Representations of Buyer.    Except as set forth in a section of the
Buyer Disclosure Schedule delivered concurrently herewith corresponding to the applicable sections of this Section 3.2 to which such disclosure
applies, Buyer hereby represents and warrants to each Seller that: 

        (a)    Organization; Qualification.    Buyer has the requisite power and authority to execute and deliver this
Agreement, to carry out its obligations hereunder and to consummate the transactions contemplated hereby. The execution and delivery by Buyer of this Agreement, its performance of its obligations
hereunder and the consummation of the transactions contemplated hereby have been duly and validly authorized by Buyer and no other actions or proceedings on the part of Buyer to authorize the
execution and delivery of this Agreement, the performance by Buyer of the obligations hereunder or the consummation of the transactions contemplated hereby. This Agreement has been duly executed and
delivered by Buyer and constitutes a legal, valid and binding agreement of Buyer, enforceable against Buyer in accordance with its terms, subject to bankruptcy, insolvency, fraudulent transfer,
reorganization, moratorium and similar laws of general applicability relating to or affecting creditors' rights and to general equitable principles. 

        (b)    No Violations.    Neither the execution and delivery of this Agreement by Buyer, the performance by Buyer of
its obligations under this Agreement, nor the consummation by Buyer of the transactions contemplated hereby nor compliance by Buyer with any of the provisions herein will (i) result in a
violation or breach of or conflict with the Partnership Agreement or Buyer's certificate of limited partnership, (ii) result in a violation or breach of or conflict with any provisions of, or
constitute a default (or an event which, with notice or lapse of time or both, would constitute a default) under, or result in the termination, cancellation of, or give rise to a right of purchase
under, or accelerate the performance required by, or result in a right of termination or acceleration under, or result in the creation of any Encumbrance upon any of the properties, rights or assets
owned or operated by Buyer, or result in being declared void, voidable, or without further binding effect, or otherwise result in a detriment to Buyer under any of the terms, conditions or provisions
of any note, bond, mortgage, indenture, deed of trust, license, contract, lease, agreement or other instrument or obligation of any kind to which Buyer is a party or by which Buyer or any of his or
its respective properties, rights or assets may be bound, (iii) violate any Orders or Laws applicable to Buyer or any of his properties, rights or assets, except in the case of
clauses (ii) and (iii) as would not have a Material Adverse Effect. 

        (c)    Consents and Approvals.    No consent, approval, Order or authorization of, or registration, declaration or
filing with, any Governmental Authority is necessary to be obtained or made by Buyer in connection with Buyer's execution, delivery and performance of this Agreement or the consummation by Buyer of
the transactions contemplated by this Agreement, except as provided under Section 4.2, or as would not have a Material Adverse Effect. 

        (d)    Absence of Litigation.    There is no action, litigation or proceeding pending and no Order of any Governmental
Authority outstanding nor, to the knowledge of Buyer, is any such action, litigation, proceeding or Order threatened, against Buyer which may prevent or materially delay Buyer from performing his
obligations under this Agreement or consummating the transactions contemplated hereby on a timely basis, except as would not have a Material Adverse Effect. 

        (e)    Independent Investigation.    Buyer has conducted its own independent investigation, review and analysis of the
business, operations, assets, liabilities, results of operations, financial condition and prospects of the Company which investigation, review and analysis was done by Buyer and, to the extent Buyer
deemed necessary or appropriate, by its representatives. 

        (f)    Investment Intent; Investment Experience; Restricted Securities.    In acquiring the Class B Membership
Interests, Buyer is not offering or selling, and shall not offer or sell the Class B Membership Interests, in connection with any distribution of any of such Class B Membership
Interests, and Buyer shall not participate in any such undertaking or in any underwriting of such 

7

 

an
undertaking, except in compliance with applicable federal and state securities Laws. Buyer acknowledges that it can bear the economic risk of its investment in the Class B Membership
Interests, and has such knowledge and experience in financial and business matters that it is capable of evaluating the merits and risks of an investment in the Class B Membership Interests.
Buyer is an "accredited investor" as such term is defined in Regulation D under the Securities Act. Buyer understands that none of the Class B Membership Interests shall have been
registered pursuant to the Securities Act or any applicable state securities Laws, that all of such Class B Membership Interests shall be characterized as "restricted securities" under federal
securities Laws and that under such Laws and applicable regulations none of such Class B Membership Interests can be sold or otherwise disposed of without registration under the Securities Act
or an exemption therefrom. 

        (g)    Capitalization.    As of the date hereof, there are [36,500,455] Common Units issued
and outstanding, and all of such Common Units and the limited partner interests represented thereby were duly authorized and validly issued in accordance with the Partnership Agreement and are fully
paid (to the extent required under the Partnership Agreement) and nonassessable (except as such nonassessability may be affected by the Delaware LP Act and the Partnership Agreement). As of the date
hereof, the Company owns a [2.0]% general partner interest in the Buyer and all of the IDRs, and such general partner interest was duly authorized and validly issued in
accordance with the Partnership Agreement. As of the date hereof, except as Previously Disclosed in Schedule 3.2(g) of the Buyer Disclosure
Schedule, Buyer has no equity securities authorized and reserved for issuance, Buyer does not have any Rights issued or outstanding with respect to its equity securities, and Buyer does not have any
commitment to authorize, issue or sell any such equity securities or Rights, except pursuant to this Agreement. The number of Common Units that are issuable upon exercise of any employee or director
options to purchase Common Units or Subordinated Units as of the date hereof are Previously Disclosed in Schedule 3.2(g) of the Buyer Disclosure
Schedule. 

        (h)    Financial Reports and SEC Documents.    Buyer's annual report on Form 10-K for the fiscal
year ended December 31, 2006, and all other reports, registration statements, definitive proxy statements or information statements filed or to be filed by Buyer or any of its Subsidiaries
subsequent to December 31, 2004 under the Securities Act, or under Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act, in the form filed, or to be filed (collectively, its
"SEC Documents"), with the SEC (i) complied or will comply in all material respects as to form with the applicable requirements under the
Securities Act or the Exchange Act, as the case may be, and (ii) did not 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 made therein, in light of the circumstances under which they were made, not misleading; and each of the balance sheets contained in or incorporated by
reference into any such SEC Document (including the related notes and schedules thereto) fairly presents the financial position of the Buyer as of its date, and each of the statements of income and
changes in partners' equity and cash flows in such SEC Documents (including any related notes and schedules thereto) fairly presents the results of operations, changes in partners' equity and changes
in cash flow of Buyer for the periods to which it relates, in each case in accordance with GAAP consistently applied during the periods involved, except in each case as may be noted therein, subject
to normal year-end audit adjustments in the case of unaudited statements. Except as and to the extent set forth on its balance sheet as of December 31, 2006, as of such date,
neither Buyer nor any of its Subsidiaries had any liabilities or obligations of any nature (whether accrued, absolute, contingent or otherwise) that would be required to be reflected on, or reserved
against in, a balance sheet or in the notes thereto prepared in accordance with GAAP consistently applied. 

8

 

        (i)    No Brokers.    No action has been taken by Buyer that would give rise to any valid claim against any party
hereto for a brokerage commission, finder's fee or other like payment with respect to the transactions contemplated by this Agreement, excluding, fees to be paid by Buyer to Lehman
Brothers Inc. and RBC Capital Markets in connection with the transactions contemplated by the Merger Agreement and this Agreement. 

        (j)    No Material Adverse Change.    Except as disclosed in its SEC Documents filed with the SEC on or before the
date hereof, since December 31, 2006, (i) Buyer and its Subsidiaries have conducted their respective businesses in the ordinary and usual course (excluding the incurrence of expenses
related to this Agreement and the transactions contemplated hereby), (ii) Buyer has not made any material change in its accounting methods, principles or practices or its Tax methods, practices
or elections and (iii) no event has occurred or circumstance arisen that, individually or taken together with all other facts, circumstances and events is reasonably likely to result in a
Material Adverse Effect. 

        (k)    Conflicts Committee Action.    At a meeting duly called and held, the Conflicts Committee determined that
[this Agreement and the transactions contemplated hereby, together with the Merger Agreement and the transaction contemplated thereby], are fair and reasonable to, and in the
best interests of, the Unaffiliated Common Unitholders and the Partnership, and recommended that the Board of Directors of the Company approve this Agreement and the transactions contemplated hereby. 

        (l)    Energy Partners Fairness Opinion.    Lehman Brothers Inc. has delivered to the Conflicts Committee its
written opinion dated as of the date hereof, that as of such date, the Redemption/Merger Consideration paid in the Redemption and the Merger and the consideration paid to the Sellers pursuant to this
Agreement, in the aggregate, are fair, from a financial point of view, to the Unaffiliated Common Unitholders. 

        (m)    Limitation of Representations and Warranties.    EXCEPT FOR THE REPRESENTATIONS AND WARRANTIES SET FORTH IN
THIS SECTION 3.2, BUYER IS NOT MAKING ANY OTHER REPRESENTATIONS OR WARRANTIES, WRITTEN OR ORAL, STATUTORY, EXPRESS OR IMPLIED. 

 
 

ARTICLE IV
  ADDITIONAL AGREEMENTS, COVENANTS, RIGHTS AND OBLIGATIONS    
    

        Section 4.1    Commercially Reasonable Best Efforts; Further Assurances.    From and
after the date hereof, upon the terms and subject to the conditions hereof, the Buyer and each Seller shall use its or his commercially reasonable best efforts to take, or cause to be taken, all
appropriate action, and to do or cause to be done, all things necessary, proper or advisable under applicable Laws to consummate and make effective the transactions contemplated by this Agreement.
Without limiting the foregoing but subject to the other terms of this Agreement, the parties hereto agree that, from time to time, whether before, at or after the Closing Date, each of them will
execute and deliver, or cause to be executed and delivered, such instruments of assignment, transfer, conveyance, endorsement, direction or authorization as may be necessary to consummate and make
effective such transactions. 

        Section 4.2    Registration Rights Agreement.    On the Closing Date, Buyer and each of
the Sellers shall execute and deliver the Registration Rights Agreement, in the form attached hereto as Exhibit E pursuant to which Buyer will
agree to grant certain registration rights to the Sellers with respect to Common Units they may hold as a result of the Merger. 

        Section 4.3    No Solicitation.    Each Seller agrees that he or it will not, and shall
use his or its reasonable best efforts to cause his or its Representatives not to, directly or indirectly through another Person, (i) solicit, initiate or encourage or facilitate, any proposal
to acquire all or a portion of such 

9

 

Seller's
Class B Membership Interest (a "Class B Proposal") or the making or consummation thereof, (ii) enter into, continue or
otherwise participate in any discussions or negotiations regarding, or furnish to any person any information in connection with, or otherwise cooperate in any way with, any such Class B
Proposal, (iii) waive, terminate, modify or fail to enforce any provision of any "standstill" or similar obligation of any person other than Buyer, (iv) approve, adopt or recommend, or
publicly propose to approve, adopt or recommend, execute or enter into, any letter of intent, memorandum of understanding, agreement in principle, merger agreement, acquisition agreement, option
agreement, joint venture agreement, partnership agreement, or other similar contract or any tender or exchange offer providing for, with respect to, or in connection with, any such Class B
Proposal or (v) agree or publicly propose to do any of the foregoing. Without limiting the foregoing, it is agreed that any violation of the restrictions set forth in the preceding sentence by
any Representative of a Seller shall be a breach of this Section 4.3 by such Seller. Each Seller hereby represents that, as of the date hereof,
such Seller is not engaged in any discussions or negotiations with respect to any Class B Proposal other than with Buyer and agrees not to, and shall use his or its best efforts to cause such
Seller's Representatives to, immediately cease and cause to be terminated all existing discussions or negotiations with any Person conducted heretofore with respect to any Class B Proposal and
will take commercially reasonable steps to inform his or its Representatives of the obligations undertaken by such Seller pursuant to this Agreement, including this  Section 4.3. 

        Section 4.4    Expenses.    Whether or not the transactions contemplated by this
Agreement are consummated, all reasonable and documented costs and expenses incurred of the Sellers in connection with this Agreement, including legal fees, accounting fees, financial advisory fees
and other professional and non-professional fees and expenses of the Sellers, up to a maximum of $10,000 per Seller, shall be reimbursed or paid by the Buyer, except to the extent
otherwise provided in this Agreement. 

        Section 4.5    Public Announcements.    No Seller will issue any press release or other
written statement for general circulation or otherwise make a public announcement relating to the transactions contemplated hereby without the prior approval of the Buyer and the Conflicts Committee. 

        Section 4.6    Reimbursement for Certain Contributions to the Company.    If after the
date of this Agreement and prior to the Closing Date, the Buyer issues Common Units or other equity securities other than pursuant to this Agreement and, in connection therewith, any Seller makes one
or more capital contributions to the Company pursuant to Section 3.5 of the Company LLC Agreement in connection with the Company's obligation to make a capital contribution to the Buyer
pursuant to Section 5.2(b) of the Partnership Agreement (a "GP Capital Contribution"), such Seller shall promptly give notice to the Buyer
thereof and provide such other documents, information and materials as the Buyer may reasonably request documenting such GP Capital Contribution, and upon Closing, Buyer shall reimburse each Seller
for the amount of any GP Capital Contribution made by such Seller. 

        Section 4.7    Seller Capacity.    Each Seller has entered into this Agreement solely
in the capacity as the beneficial owner of such Seller's Class B Membership Interest; provided nothing herein shall in any way restrict or limit any Seller from taking any action in his
capacity as a director or officer of the Company or of Hydrocarbon or otherwise fulfilling his or her fiduciary obligations as director or officer of the Company or of Hydrocarbon. 

        Section 4.8    Distributions.    Until the Closing Date, all Class B Members
shall continue to be entitled to distributions to be paid pursuant to the Company LLC Agreement. 

        Section 4.9    Legends.    The certificate or certificates representing the Common
Units issued pursuant to Section 2.1(b) shall bear a legend that such shares have not been registered under the Securities Act or any state securities. 

10

 

 
 

ARTICLE V
  CLOSING CONDITIONS    
    

        Section 5.1    Mutual Conditions.    The respective obligation of the Buyer and each of
the Sellers to consummate the purchase and issuance and sale of the Purchased Units shall be subject to the satisfaction on or prior to the Closing Date of each of the following conditions (any or all
of which may be waived by a particular Party on behalf of itself in writing, in whole or in part, to the extent permitted by applicable Law): 

        (a)   no
order, decree or injunction of any court or agency of competent jurisdiction shall be in effect, and no Law shall have been enacted or adopted, that enjoins,
prohibits or makes illegal consummation of any of the transactions contemplated hereby, and no action, proceeding or investigation by any Governmental Authority with respect to this Agreement or the
transactions contemplated hereby shall be pending that seeks to restrain, enjoin, prohibit or delay consummation of such transaction or to impose any material restrictions or requirements thereon or
Buyer or any Seller with respect thereto; provided, however, that prior to invoking this condition, each
party shall have complied fully with its obligations under Section 4.1; 

        (b)   all
filings required to be made prior to the Closing Date with, and all other consents, approvals, permits and authorizations required to be obtained prior to the
Closing Date from, any Governmental Authority in connection with the execution and delivery of this Agreement and the consummation of the transactions contemplated hereby by the parties hereto or
their Affiliates shall have been made or obtained; 

        (c)   the
Buyer and Hydrocarbon shall have concurrently closed the Merger. 

        Section 5.2    Buyer's Conditions.    The obligation of the Buyer to consummate the
purchase from, and contribution by, each Seller of such Seller's Class B Membership Interests shall be subject to the satisfaction on or prior to the Closing Date of each of the following
conditions with respect to each Seller individually and not the Sellers jointly (any or all of which may be waived by the Buyer in writing, in whole or in part, to the extent permitted by applicable
Law): 

        (a)   the
representations and warranties of such Seller contained in this Agreement that are qualified by materiality or Material Adverse Effect shall be true and correct when
made and as of the Closing Date and all other representations and warranties shall be true and correct in all material respects when made and as of the Closing Date, in each case as though made at and
as of the Closing Date (except that representations made as of a specific date shall be required to be true and correct as of such date only); 

        (b)   such
Seller shall have performed and complied with the covenants and agreements contained in this Agreement that are required to be performed and complied with by such
Seller on or prior to the Closing Date; and 

        (c)   such
Seller shall have delivered to Buyer all of the documents, certificates and other instruments required to be delivered under, and otherwise complied with the
provisions of, Section 2.3. 

        Section 5.3    Sellers' Conditions.    The respective obligation of each Seller to
consummate the sale and contribution of such Seller's Class B Membership Interests shall be subject to the satisfaction on or prior to the Closing Date of each of the following conditions (any
or all of which may be waived by the Sellers, in whole or in part, to the extent permitted by applicable Law): 

        (a)   the
representations and warranties of Buyer contained in this Agreement that are qualified by materiality or Material Adverse Effect shall be true and correct when made
and as of the Closing Date and all other representations and warranties shall be true and correct in all material respects when made and as of the Closing Date, in each case as though made at and as
of 

11

 

the
Closing Date (except that representations made as of a specific date shall be required to be true and correct as of such date only); 

        (b)   Buyer
shall have performed and complied with the covenants and agreements contained in this Agreement that are required to be performed and complied with by Buyer on or
prior to the Closing Date; and 

        (c)   Buyer
shall have delivered to each Seller all of the documents, certificates and other instruments required to be delivered under, and otherwise complied with the
provisions of, Section 2.4. 

 
 

ARTICLE VI
  TERMINATION    
    

        Section 6.1    Termination.    Notwithstanding anything herein to the contrary, this
Agreement may be terminated at any time prior to Closing: 

        (a)   by
the mutual consent of Buyer and any Seller on behalf of such Seller in a written instrument; 

        (b)   by
Buyer, or any Seller on behalf of such Seller, after February 27, 2008, if the Closing has not occurred by such date;  provided that as of such date the terminating party is not in default under
this Agreement; 

        (c)   if
a statute, rule, order, decree or regulation shall have been enacted or promulgated, or if any action shall have been taken by any Governmental Authority of competent
jurisdiction which permanently restrains, precludes, enjoins or otherwise prohibits the consummation of the transactions contemplated by this Agreement or makes the transactions contemplated by this
Agreement illegal; 

        (d)   by
either the Buyer, on the one hand, or any Seller (solely with respect to such Seller) on the other hand, in writing without prejudice to other rights and remedies
which the terminating party or its Affiliates may have (provided the terminating party and its Affiliates are not otherwise in material default or breach of this Agreement, or have not failed or
refused to close without justification hereunder), if the other party (i) has materially failed to perform its covenants or agreements contained herein required to be performed on or prior to
the Closing Date, or (ii) has materially breached any of its representations or warranties contained herein; provided,  however, that in the case of
clause (i) or (ii), the defaulting party shall have a period of thirty (30) days following written notice
from the non-defaulting party to cure any breach of this Agreement, if such breach is curable; or 

        (e)   automatically,
without any action on the part of Buyer or any Seller, at any time prior to Closing, upon the public announcement of the termination of the Merger
Agreement. 

        Section 6.2    Effect of Termination.    If a party terminates this Agreement as
provided in Section 6.1 above, such termination shall be without liability and none of the provisions of this Agreement shall remain effective or
enforceable, except for those contained in Section 4.4, this Section 6.2 and  Article VIII.
Notwithstanding and in addition to the foregoing, in the event that this Agreement is terminated pursuant to  Section 6.1(d) or if any party is otherwise in breach of this Agreement, (a) such
breaching party or parties shall remain liable for its
or their obligations under Article VII and (b) such termination shall not relieve such breaching party of any liability for a willful
breach of any covenant or agreement under this Agreement or be deemed a waiver of any available remedy (including specific performance, if available) for any such breach. 

12

 
 
 

ARTICLE VII
  INDEMNIFICATION    
    

        Section 7.1    Seller's Indemnity.    Each Seller shall indemnify and hold harmless
Buyer and its respective officers, directors and employees (the "Indemnified Parties") from any and all claims, liabilities, damages, penalties,
judgments, assessments, losses, costs, expenses, including reasonable attorneys' fees and expenses, incurred by Buyer in seeking indemnification under this Agreement in connection with the breach of a
representation or warranty set forth in paragraphs (a) through (i) of  Section 3.1 by such Seller. The
liability of each Seller under this Section 7.1 shall not
exceed 50% of the Aggregate Consideration Value received by such Seller pursuant to this Agreement. 

        Section 7.2    Survival.    In the event of termination of this Agreement pursuant to
Section 6.1, all rights and obligations of the parties hereto under this Agreement shall terminate, except the provisions of Section 4.4,  Section 6.2, this Article VII and  Article VIII shall survive such termination; provided that nothing herein shall relieve any party
hereto from any liability for any material breach by such party of any of its representations, warranties, covenants or agreements set forth in this Agreement and all rights and remedies of a
nonbreaching party under this Agreement in the case of such a material breach, at law or in equity, shall be preserved. In the event the Closing occurs, the representations and warranties of Seller
and Buyer contained in paragraphs (a) through (i) of  Section 3.1 shall survive the Closing
indefinitely. Other than the obligations contained in paragraphs
(a) through (i) of Section 3.1,  Section 4.1, Section 4.2,  Section 4.4, Section 4.6, this
Article VII and Article VIII, none of the representations, warranties, agreements,
covenants or obligations in this Agreement or in any instrument delivered pursuant to this Agreement shall survive the Closing. 

        Section 7.3    Enforcement of this Agreement.    The parties hereto acknowledge and
agree that an award of money damages would be inadequate for any breach of this Agreement by any party and any such breach would cause the non-breaching parties irreparable harm.
Accordingly, the parties hereto agree that, in the event of any breach or threatened breach of this Agreement by one of the parties, the parties will also be entitled, without the requirement of
posting a bond or other security, to equitable relief, including injunctive relief and specific performance, provided such party is not in material default hereunder. Such remedies will not be the
exclusive remedies for any breach of this Agreement but will be in addition to all other remedies available at law or equity to each of the parties. 

        Section 7.4    No Waiver Relating to Claims for Fraud or Willful Misconduct.    The
liability of any party under this Article VII shall be in addition to, and not exclusive of, any other liability that such party may have at law
or in equity based on such party's (a) fraudulent acts or omissions or (b) willful misconduct. None of the provisions set forth in this Agreement shall be deemed to be a waiver by or
release of any party of any right or remedy that such party may have at law or equity based on any other party's fraudulent acts or omissions or willful misconduct nor shall any such provisions limit,
or be deemed to limit, (i) the amounts of recovery sought or awarded in any such claim for fraud or willful misconduct, (ii) the time period during which a claim for fraud or willful
misconduct may be brought, or (iii) the recourse that any such party may seek against another party with respect to a claim for fraud or willful misconduct. 

 
 

ARTICLE VIII
  MISCELLANEOUS    
    

        Section 8.1    Notices.    All notices and demands provided for hereunder shall be in
writing and shall be given by regular mail, registered or certified mail, return receipt requested, facsimile, air courier guaranteeing overnight delivery, electronic mail or personal delivery to the
address listed below, in the case of Buyer, or the addresses listed in Schedule 8.1, in the case of the respective Sellers, or to such other
address as the Buyer or a Seller may designate in writing. All notices and communications 

13

 

shall
be deemed to have been duly given: at the time delivered by hand, if personally delivered; when notice that the recipient has read the message, if sent via electronic mail; upon actual receipt,
if sent by registered or certified mail, return receipt requested, or regular mail, if mailed; when receipt acknowledged, if sent via facsimile; and upon actual receipt when delivered to an air
courier guaranteeing overnight delivery; provided, that copies to be delivered below or on such schedule shall not be required for effective notice and
shall not constitute notice. 

If
to Buyer, addressed to: 

MarkWest
Energy Partners, L.P.

1515 Arapahoe St.

Tower 2, Suite 700

Denver, CO 80202

Attention: Board of Directors/Conflicts Committee

Telecopy: (303) 662-8870 

with
a copy to: 

MarkWest
Energy Partners, L.P.

1515 Arapahoe St.

Tower 2, Suite 700

Denver, CO 80202

Attention: General Counsel

Telecopy: (303) 925-9308 

with
a copy to: 

Vinson &
Elkins L.L.P.

666 Fifth Avenue 26th Floor

New York, NY 10103-0040

Attention: Michael J. Swidler

Telecopy: (917) 849-5367 

with
a copy to: 

Andrews
Kurth LLP

1350 I Street, NW

Suite 1100

Washington, DC 20005

Attention: Bill Cooper

Telecopy: (202) 974-9537 

        Section 8.2    Waiver and Amendment; Entire Agreement.    Subject to compliance with
applicable Law, prior to the Closing, any provision of this Agreement may be (a) waived in writing by any of the Sellers individually, or the Conflicts Committee, on behalf of the Buyer, or
(b) amended or modified as to any Seller individually at any time by an agreement in writing between any such Seller individually, and the Conflicts Committee, on behalf of the Buyer. At any
time prior to Closing, upon the request of the Sellers, the Buyer agrees to amend this Agreement solely for the purpose of changing the amount of cash to be paid and/or the number of units to be
issued to one or more of the Sellers as reflected in Schedule 2.1, as they may request in writing,  provided that any such changes do not increase the
total amount of cash or the total number of Common Units to be issued by the Buyer pursuant to
Section 2.1 and do not change the aggregate value of the cash to be paid and the Common Units to be issued to any individual Seller, as reflected in the far right-hand column on  Schedule 2.1,
assuming a value per Common Unit equal to the Common Unit Price; and provide, further, that any such amendment shall be agreed to
in writing by the Buyer and each the Sellers. The Buyer and each of the 

14

 

Sellers
further agree that, at any time prior to Closing, upon the request of any holder of Class B Membership Interests not that is not a party to this Agreement (a
"Requesting Holder"), the Buyer, each Seller and any such Requesting Holder shall enter into an amendment to this Agreement solely for the purpose of
making such Requesting Holder a party to this Agreement and to modify Schedule 2.1 reflect the amount of cash to be paid and the number of Common
Units to be issued to such Requesting Holder; provided, that the aggregate amount of cash and the aggregate number of Common Units to be paid or issued
to any one or more Requesting Holders shall not exceed the amount and number set forth on Schedule 8.2; and  provided, further, that any such Requesting Holder must agree to accept all of the responsibilities and
obligations as a Seller under this Agreement and any such amendment shall be agreed to in writing by the Buyer, each the Sellers and such Requesting Holder. 

        This
Agreement, the Merger Agreement and the agreements contemplated by the Merger Agreement represent the entire understanding of the parties hereto with reference to the transactions
contemplated hereby and supersedes any and all other oral or written agreements heretofore made. 

        Section 8.3    Binding Effect and Assignment.    This Agreement shall be binding upon
and inure to the benefit of the parties hereto and their respective permitted successors and assigns. Except as contemplated in Section 7.1,
nothing in this Agreement, express or implied, is intended to confer upon any person other than the Parties hereto and their respective permitted successors and assigns, any rights, benefits or
obligations hereunder. No Party hereto may assign, transfer, dispose of or otherwise alienate this Agreement or any of its rights, interests or obligations under this Agreement (whether by operation
of law or otherwise), except in the case of a Seller that is a natural person, by probate to such Seller's estate; provided that Buyer may assign its
rights under this Agreement to an Affiliate of Buyer, but any such assignment shall not relieve Buyer of its obligations hereunder. Any attempted assignment, transfer, disposition or alienation in
violation of this Agreement shall be null, void and ineffective. 

        Section 8.4    Severability.    If any term or other provision of this Agreement is
invalid, illegal, or incapable of being enforced by any rule of applicable Law, or public policy, all other conditions and provisions of
this Agreement shall nevertheless remain in full force and effect so long as the economic or legal substance of the transactions contemplated by this Agreement are not affected in any manner
materially adverse to any party hereto. Upon such determination that any term or other provision is invalid, illegal, or incapable of being enforced, the parties hereto shall negotiate in good faith
to modify this Agreement so as to effect the original intent of the parties hereto as closely as possible in a mutually acceptable manner in order that the transactions contemplated by this Agreement
are consummated as originally contemplated to the fullest extent possible. 

        Section 8.5    Headings.    The headings contained in this Agreement are for reference
purposes only and are not part of this Agreement. 

        Section 8.6    Governing Law; Jurisdiction.    This Agreement shall be governed by, and
interpreted in accordance with, the laws of the State of Delaware, without regard to the conflict of law principles thereof (except to the extent that mandatory provisions of federal or Delaware law
govern). parties hereto agree that any suit, action or proceeding seeking to enforce any provision of, or based on any matter arising out of or in connection with, this Agreement or the transactions
contemplated hereby shall be brought in any federal court located in the State of Colorado (or state court if subject matter jurisdiction prevents maintaining an action in federal court), and each of
the Parties hereby irrevocably consents to the jurisdiction of such courts (and of the appropriate appellate courts therefrom) in any such suit, action or proceeding and irrevocably waives, to the
fullest extent permitted by law, any objection that it may now or hereafter have to the laying of the venue of any such suit, action or proceeding in any such court or that any such suit, action or
proceeding brought in any such court has been brought in an inconvenient forum. Process in any such suit, action or proceeding may be served 

15

 

on
any party anywhere in the world, whether within or without the jurisdiction of any such court. Without limiting the foregoing, each party agrees that service of process on such Party as provided in  Section 8.1 shall be deemed effective service of process on such Party. 

        Section 8.7    Waiver of Jury Trial.    EACH OF THE PARTIES HERETO HEREBY IRREVOCABLY
WAIVES ANY AND ALL RIGHT TO TRIAL BY JURY IN ANY LEGAL PROCEEDING ARISING OUT OF OR RELATED TO THIS AGREEMENT OR THE TRANSACTIONS CONTEMPLATED HEREBY. 

        Section 8.8    Negotiated Agreement.    The provisions of this Agreement were
negotiated by the parties hereto, and this Agreement shall be deemed to have been drafted by all of the parties hereto. 

        Section 8.9    Counterparts.    This Agreement may be executed in one or more
counterparts, each of which shall be deemed to constitute an original. 

        Section 8.10    No Act or Failure to Act.    No act or failure to act shall constitute
a breach by Buyer of this Agreement unless such act or failure to act is expressly approved by the Conflicts Committee. 

16

        IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be signed by their respective officers hereunto duly authorized, all as of the date first written above. 

	 	 	MARKWEST ENERGY PARTNERS, L.P.
	

 	
 	

By:	
 	

MarkWest Energy GP, L.L.C., its general partner
	

 	
 	

By:	
 	

 Name:  Nancy K. Buese

Title:    Chief Financial Officer

Signature Page to

Class B Membership Interest Contribution Agreement  

	 	 	Frank M. Semple
	

 	
 	

	 	 	John M. Fox
	

 	
 	

	 	 	Randy S. Nickerson
	

 	
 	

	 	 	John C. Mollenkopf
	

 	
 	

	 	 	Donald C. Heppermann
	

 	
 	

	 	 	Andrew L. Schroeder
	

 	
 	

	 	 	Jan Kindrick
	

 	
 	

	

 	
 	

Cindy Kindrick
	

 	
 	

	

 	
 	
I, the spouse of Jan Kindrick, have read and hereby approve the foregoing Agreement. In consideration of Buyer granting my spouse the right to transfer and convey his Class B Membership Interest to Buyer on the
terms and for the consideration set forth in the Agreement, I hereby agree to be bound irrevocably by the Agreement and further agree that any community property or similar interest that I may have in the Class B Membership Interest
transferred and conveyed or the consideration received shall hereby be similarly bound. I hereby appoint my spouse as my attorney-in-fact with respect to any amendment or exercise of any right under the Agreement.

	 	 	Kevin Kubat
	

 	
 	

	 	 	Nancy K. Buese
	

 	
 	

	 	 	C. Corwin Bromley
	

 	
 	

QuickLinks

CLASS B MEMBERSHIP INTEREST CONTRIBUTION AGREEMENT dated as of September 5, 2007 by and among MARKWEST ENERGY PARTNERS, L.P., and THE SELLERS NAMED HEREIN

Table of Contents

ARTICLE IV ADDITIONAL AGREEMENTS, COVENANTS, RIGHTS AND OBLIGATIONS

ARTICLE V CLOSING CONDITIONS

ARTICLE VI TERMINATION

ARTICLE VII INDEMNIFICATION

ARTICLE VIII MISCELLANEOUS

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