(k)           “Eligible Person” means any employee or officer of the Company or any Affiliate, or any director of the Company or any Affiliate (including directors who are not employed by the Company or any Affiliate), who the Committee determines to be an Eligible Person.

(l)            “Exchange Act” means the Securities Exchange Act of 1934, as amended.

(m)          “Fair Market Value” means, with respect to any property (including, without limitation, any Shares or other securities), the fair market value of such property determined by such methods or procedures as shall be established from time to time by the Committee; provided, however, that the Fair Market Value of Shares will be determined on a reasonable basis using actual transactions in such Shares as reported on an established securities market and consistently applied in accordance with the final regulations or other guidance issued under Code Section 409A.

(n)           “Incentive Stock Option” means an option granted under Section 6(a) of the Plan that is intended to meet the requirements of Code Section 422 or any successor provision.

(o)           “Non-Qualified Stock Option” means an option granted under Section 6(a) of the Plan that is not intended to be an Incentive Stock Option.

(p)           “Option” means an Incentive Stock Option or a Non-Qualified Stock Option.

(q)           “Participant” means an Eligible Person who has been granted an Award under the Plan.

(r)            “Person” means any individual, corporation, partnership, association or trust.

(s)            “Plan” means this 2006 Stock Incentive Plan, as amended from time to time.

(t)            “Prior Plan” means the MarkWest Hydrocarbon, Inc. 1996 Stock Incentive Plan.

(u)           “Restricted Stock” means any Share granted under Section 6(c) of the Plan.

(v)           “Rule 16b-3” means Rule 16b-3 promulgated by the Exchange Act, or any successor rule or regulation.

(w)          “Securities Act” means the Securities Act of 1933, as amended.

(x)           “ Service” means a Participant’s employment or service with the Company or an Affiliate, whether in the capacity of an employee or a non-employee director.  A Participant’s Service shall not be deemed to have terminated merely because of a change in the capacity in which the Participant renders such Service or a change in the Company or Affiliate for which the Participant renders such Service, provided that there is no interruption or termination of the Participant’s Service.  Furthermore, a Participant’s Service shall not be deemed to have terminated if the Participant takes any military leave, sick leave, or other bona fide leave of absence approved by the Company.  However, if any such leave taken by a Participant exceeds ninety (90) days, then on the one hundred eighty-first (181st) day following the commencement

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of such leave any Incentive Stock Option held by the Participant shall cease to be treated as an Incentive Stock Option and instead shall be treated thereafter as a Non-Qualified Stock Option, unless the Participant’s right to return to Service with the Company or an Affiliate is guaranteed by statute or contract.  Notwithstanding the foregoing, unless otherwise designated by the Company or required by law, a leave of absence shall not be treated as Service for purposes of determining vesting under the Participant’s Award Agreement.  Subject to the foregoing, the Company, in its discretion, shall determine whether the Participant’s Service has terminated and the effective date of such termination.

(y)           “Share” means a share of Common Stock, $.01 par value, of the Company or such other securities or property as may become subject to Awards pursuant to an adjustment made under Section 4(c) of the Plan.

(z)           “Stock Appreciation Right” or “SAR” means any right granted under Section 6(b) of the Plan.

(aa)         “Termination for Cause” means, with respect to any Participant, the termination of such Participant on account of “cause” as such term is defined in the Award Agreement and, if no such definition is included in the Award Agreement, the definition of “cause” shall be that definition provided in an effective employment agreement between the Participant and the Company and, if no such effective employment agreement exists or no such definition is included in the employment agreement, “cause” shall include without limitation (i) the Participant’s felony conviction for fraud, misappropriation of Company funds, or embezzlement; (ii) the willful and unreasonable refusal by the Participant to perform the Participant’s duties or responsibilities for any reason other than illness or incapacity; or (iii) the Participant’s violation of any code of conduct, code of ethics, employment policies, or provisions of an employee handbook or other published policy (whether disseminated in writing to employees or via a website or other publication) of the Company which is applicable to the Participant, as in effect from time to time.  Whether a termination is for “cause” will be determined solely by the Committee in its sole discretion.  Notwithstanding the above, if evidence of “cause” is acquired after any termination that originally was not a Termination for Cause, the termination may, in the discretion of the Committee, be treated as a Termination for Cause for purposes of this Plan.

Section 3.              Administration .

(a)           Power and Authority of the Committee .  The Plan shall be administered by the Committee.  Subject to the express provisions of the Plan and to applicable law, the Committee shall have full power and authority to: (i) designate Participants; (ii) determine the type or types of Awards to be granted to each Participant under the Plan; (iii) determine the number of Shares to be covered by (or with respect to which payments, rights or other matters are to be calculated in connection with) each Award; (iv) determine the terms and conditions of any Award or Award Agreement; (v) amend the terms and conditions of any Award or Award Agreement and accelerate the exercisability of Options or the lapse of restrictions relating to Restricted Stock; (vi) determine whether, to what extent and under what circumstances Awards may be exercised in cash, Shares, other securities, other Awards or other property, or canceled, forfeited or suspended; (vii) determine whether, to what extent and under what circumstances cash, Shares, other securities, other Awards, other property and other amounts payable with respect to an

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Award under the Plan shall be deferred either automatically or at the election of the holder thereof or the Committee; (viii) interpret and administer the Plan and any instrument or agreement relating to, or Award made under, the Plan; (ix) establish, amend, suspend or waive such rules and regulations and appoint such agents as it shall deem appropriate for the proper administration of the Plan; and (x) make any other determination and take any other action that the Committee deems necessary or desirable for the administration of the Plan.  Unless otherwise expressly provided in the Plan, all designations, determinations, interpretations and other decisions under or with respect to the Plan or any Award shall be within the sole discretion of the Committee, may be made at any time and shall be final, conclusive and binding upon any Participant, any holder or beneficiary of any Award and any employee of the Company or any Affiliate.  In exercising its authority pursuant to the Plan, the Committee shall adhere to all provisions of the Code as are applicable to the grant, issuance and exercise of any Award.

(b)           Administration with Respect to Insiders .  With respect to participation by officers and directors of the Company, and any other person whose transactions in Shares are subject to Section 16 of the Exchange Act, at any time that any class of equity security of the Company is registered pursuant to Section 12 of the Exchange Act, the Plan shall be administered in compliance with the requirements, if any, of Rule 16b-3 under the Exchange Act.

(c)           Administration Complying with Code Section 162(m) .  If the Company is a “publicly held corporation” within the meaning of Code Section 162(m), the Board may establish a Committee of “outside directors” within the meaning of Code Section 162(m) to approve the grant of any Award which might reasonably be anticipated to result in the payment of employee remuneration that otherwise would exceed the limit on employee remuneration deductible for income tax purposes pursuant to Code Section 162(m).

(d)           Delegation .  Subject to the provisions set forth above, the Committee may delegate its powers and duties under the Plan to one or more officers of the Company or any Affiliate or a committee of such officers, subject to such terms, conditions and limitations as the Committee may establish in its sole discretion.

(e)           Indemnification .  In addition to such other rights of indemnification as they may have as members of the Board or the Committee or as officers or employees of the Company or any Affiliate, members of the Board or the Committee and any officers or employees of the Company or any Affiliate to whom authority to act for the Board, the Committee or the Company is delegated shall be indemnified by the Company against all reasonable expenses, including attorneys’ fees, actually and necessarily incurred in connection with the defense of any action, suit or proceeding, or in connection with any appeal therein, to which they or any of them may be a party by reason of any action taken or failure to act under or in connection with the Plan, or any right granted hereunder, and against all amounts paid by them in settlement thereof (provided such settlement is approved by independent legal counsel selected by the Company) or paid by them in satisfaction of a judgment in any such action, suit or proceeding, except in relation to matters as to which it shall be adjudged in such action, suit or proceeding that such person is liable for gross negligence, bad faith or intentional misconduct in duties; provided, however, that within sixty (60) days after the institution of such action, suit or proceeding, such person shall offer to the Company, in writing, the opportunity at its own expense to handle and defend the same.

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Section 4.              Shares Available for Awards .

(a)           Shares Available .  Subject to adjustment as provided in Section 4(c), the number of Shares available for granting Awards under the Plan shall be 1,000,000 which includes those Shares available as of the Effective Date under the Prior Plan.  To the extent any Award under this Plan is exercised or cashed out or terminates or expires or is forfeited without a payment being made to the Participant in the form of Shares, the shares subject to such Award that were not so paid, if any, shall again be available for distribution in connection with Awards under the Plan.  If a SAR is exercised, only the number of Shares issued, if any, will be deemed delivered for purposes of determining the maximum number of Shares available for delivery under the Plan.  Any Shares that are used by a Participant as full or partial payment of withholding or other taxes or as payment for the exercise price of an Award under the Plan shall be available for distribution in connection with Awards under the Plan.

(b)           Shares Under Prior Plan .  Except as otherwise provided herein, any Award made under the Prior Plan before the expiration of such Prior Plan shall continue to be subject to the terms and conditions of such Prior Plan and the applicable Award Agreement.

(c)           Adjustments .

(i)            In the event of any merger, reorganization, consolidation, recapitalization, reclassification, distribution, stock dividend, stock split, reverse stock split, split-up, spin-off, combination, repurchase or exchange of shares, issuance of rights or warrants or other similar transaction or event affecting the Shares, the Committee is authorized to make such adjustments or substitutions with respect to the Plan and to Awards granted thereunder as it deems appropriate to reflect the occurrence of such event, including, but not limited to, adjustments (1) to the aggregate number and kind of securities reserved for issuance under the Plan, (2) to the Award limits set forth in Section 5(c), and (3) to the number and kind of securities subject to outstanding Awards and, if applicable, the grant or exercise price of outstanding Awards.

(ii)           In connection with a spin-off or similar corporate transaction, the adjustments described in this Section 4(c) may include, but are not limited to, the assumption of the Award or the substitution of comparable Stock Options to purchase the stock of another entity or Stock Appreciation Rights reflecting the securities of another entity, which may be settled in the form of cash, Shares, stock of such other entity, or other securities or property, as determined by the Committee; and, in the event of such a substitution, references in this Plan and in the applicable Award agreement thereunder to “Shares” shall be deemed to also refer to the securities of the other entity where appropriate.

(iii)          Notwithstanding the above, the number of Shares covered by any Award or to which such Award relates always shall be a whole number.

Section 5.              Eligibility .

(a)           Designation of Participants .  Any Eligible Person shall be eligible to be designated a Participant.  In determining which Eligible Persons shall receive an Award and the terms of any Award, the Committee may take into account the nature of the services rendered by the respective Eligible Persons, their present and potential contributions to the success of the

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Company or such other factors as the Committee, in its discretion, shall deem relevant.  Eligibility in accordance with this Section shall not entitle any person to be granted an Award or, having been granted an Award, to be granted an additional Award.

(b)           Incentive Stock Option Limitations .

(i)            Persons Eligible .  An Incentive Stock Option may be granted only to a person who, on the effective date of grant, is an employee of the Company or a “subsidiary corporation” of the Company within the meaning of Code Section 424(f) (each being an “ISO-Qualifying Corporation”).  Any person who is not an employee of an ISO-Qualifying Corporation on the effective date of the grant of an Option to such person may be granted only a Non-Qualified Stock Option.  An Incentive Stock Option granted to a prospective employee upon the condition that such person become an employee of an ISO-Qualifying Corporation shall be deemed granted effective on the date such person commences employment with an ISO-Qualifying Corporation, with an exercise price determined as of such date in accordance with Section 6.

(ii)           Fair Market Value Limitation .  As required by Code Section 422, to the extent that Options designated as Incentive Stock Options (granted under all stock option plans of the Participating Company Group, including the Plan) become exercisable by a Participant for the first time during any calendar year for Shares having a Fair Market Value greater than One Hundred Thousand Dollars ($100,000), the portion of such Options which exceeds such amount shall be treated as Non-Qualified Stock Options.  For purposes of this Section, Options designated as Incentive Stock Options shall be taken into a