MarkWest Energy Partners, LP (MWE)

Objectives of Compensation Program

General Objectives and Overall Philosophy

        The primary objectives of our compensation program are to attract, retain and incentivize high-quality executives through a total compensation plan that is both market competitive and performance-based and that is intended to align compensation with the Partnership's long-term financial goals and unitholder distribution growth as well as the achievement of objectives consistent with the Partnership's strategic plans. We strive to accomplish these objectives by compensating all employees, including our NEOs, with a total compensation package consisting of a combination of competitive base salary and incentive compensation. We believe that compensation should be designed to reward executives and employees for achievement of the Partnership's financial and performance plans and strategic objectives and to provide opportunities for increased compensation based on extraordinary performance by our employees, including our NEOs. Following this philosophy, in determining NEO compensation, we consider all relevant factors, such as the competition for talent, our desire to link pay with performance, the use of equity to align NEO interests with those of our unitholders, individual contributions, teamwork and performance, each NEO's total compensation package, and internal pay equity.

Pay for Performance and Alignment with Long-Term Goals

        At the core of our compensation philosophy is our strong belief that pay should be directly linked to performance. We believe in a pay for performance culture that places a significant portion of executive's total compensation as contingent upon, or variable with, individual performance, Partnership performance and achievement of strategic goals, including the goal of increasing unitholder value.

        The performance-based compensation for our executives is in the form of (i) annual cash incentives to promote achievement of, and accountability for, shorter term performance plans and strategic goals, and (ii) equity grants, designed to align the long-term interests of our executives with those of our unitholders, by creating a strong and direct link between executive compensation and unitholder return over a multiple year performance cycle. In 2008, long-term incentive equity awards were granted in phantom units issued under the Partnership's 2008 Long-Term Incentive Plan, which was approved by the Partnership's unitholders in connection with the redemption and merger with MarkWest Hydrocarbon, pursuant to an executive long-term equity incentive arrangement approved by the Compensation Committee and the Board of Directors. The phantom units granted to the executives and other key employees pursuant to this arrangement vest on a performance-based and time-based schedule over a period of three years. The 2008 Long-Term Incentive Plan and the terms of the executive long-term equity incentive arrangement for executives and other key employees are described in more detail below in this CD&A in the section entitled Elements of Executive Compensation—Incentive Compensation—Long-Term Equity Incentive Programs.

        In addition to the performance-based equity grants, prior to the redemption and merger with MarkWest Hydrocarbon, the executives and other key members of management had the opportunity to purchase from MarkWest Hydrocarbon membership interests in the Partnership's General Partner. This opportunity for General Partner ownership was provided in order to incent and retain executives and key

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Table of Contents

employees and align their interests with our long-term strategic goals. The purchase arrangements are referred to as the Participation Plan and are discussed in further detail below in this CD&A in the section entitled Elements of Executive Compensation—Participation Plan. In connection with the redemption and merger with MarkWest Hydrocarbon, the Partnership acquired these membership interests from the executives and other current and former members of management, and the General Partner became an indirect subsidiary of the Partnership as more fully described in the section above entitled Redemption and Merger with MarkWest Hydrocarbon. The terms of the purchase of the membership interests are discussed in further detail below in this CD&A in the section entitled Elements of Executive Compensation—Participation Plan and above in the section entitled Certain Relationships and Related Transactions—Redemption and Merger with MarkWest Hydrocarbon.

Base Compensation to Reflect Position and Responsibility and Competitiveness within Industry

        A key component of an executive's total compensation, base salaries are designed to compensate executives commensurate with their respective level of experience, scope of responsibilities, sustained individual performance and future potential. The goal has been to provide for base salaries that are sufficiently competitive with other similar sized energy companies and/or partnerships, both regionally and nationally, in order to attract and retain talented leaders.

Objectives of Compensation Program

General Objectives and Overall Philosophy

        The primary objectives of our compensation program are to attract, retain and challenge high quality executives through a total compensation plan that is both market competitive and performance-based and that is intended to align compensation with the Partnership's overall performance and growth in distributions to unitholders as well as the achievement of objectives consistent with the Partnership's strategic plans. We strive to accomplish these objectives by compensating all employees, including our Named Executive Officers (the "NEOs"), with a total compensation package consisting of a combination of competitive base salary and incentive compensation. We believe that compensation should be designed to reward executives for achievement of the Partnership's financial plans and strategic objectives and to provide opportunities for increased compensation based on extraordinary performance by our employees, including our NEOs. Following this philosophy, in determining NEO compensation, we consider all relevant factors, such as the competition for talent, our desire to link pay with performance, the use of equity to align NEO interests with those of our unitholders, individual contributions, teamwork and performance, each NEO's total compensation package, and internal pay equity.

Pay for Performance and Alignment with Long-Term Goals

        At the core of our compensation philosophy is our strong belief that pay should also be directly linked to performance. We believe in a pay for performance culture that places a significant portion of executive officer total compensation as contingent upon, or variable with, individual performance, Partnership performance and achievement of strategic goals, including the goal of increasing unitholder value.

        The performance-based compensation for our executives is in the form of (i) annual cash incentives to promote achievement of, and accountability for, shorter term performance plans and strategic goals, and (ii) equity grants, designed to align the long-term interests of our executive officers with those of our

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unitholders, by creating a strong and direct link between executive compensation and unitholder return over a multiple year performance cycle. In 2007, long-term incentive equity awards were granted in phantom units issued under the Partnership's Long-Term Incentive Plan, and in restricted stock issued under the MarkWest Hydrocarbon 2006 Stock Incentive Plan. These shares/units vest one-third annually over a three-year period. In October 2007, the Partnership's General Partner approved the 2008 Long-Term Incentive Plan, under which future equity awards will be granted. The Partnership's unitholders approved the 2008 Long-Term Incentive Plan in connection with the redemption and merger, and the plan is described in more detail below in this CD&A in the section entitled Elements of Executive Compensation—Incentive Compensation—Long-Term Equity Incentive Programs. In addition, in September 2007 the Compensation Committees of the General Partner and of MarkWest Hydrocarbon approved a long-term equity incentive arrangement that would provide for a grant of up to an additional 795,000 phantom units to senior executives and other key employees. This long-term equity incentive arrangement was contingent upon the closing of the redemption and merger with MarkWest Hydrocarbon and will vest on a performance-based and time-based schedule over a period of three years. The terms of this arrangement are discussed in more detail below in the section entitled Elements of Executive Compensation—Incentive Compensation—Long-Term Equity Incentive Programs.

        In addition to the performance-based equity grants, prior to the redemption and merger with MarkWest Hydrocarbon, the NEOs and other key members of management had the opportunity to purchase from MarkWest Hydrocarbon membership interests in the Partnership's General Partner. This opportunity for General Partner ownership was provided in order to incent and retain key employees and align their interests with our long-term strategic goals. The purchase arrangements are referred to as the Participation Plan and are discussed in further detail below in this CD&A in the section entitled Elements of Executive Compensation—Participation Plan. In connection with the redemption and merger with MarkWest Hydrocarbon, the Partnership acquired these membership interests from the NEOs and other current and former members of management, and the General Partner became an indirect subsidiary of the Partnership. The terms of the purchase are discussed in further detail below in this CD&A in the section entitled Elements of Executive Compensation—Participation Plan and above in the section entitled Certain Relationships and Related Transactions—Redemption and Merger with MarkWest Hydrocarbon.

Base Compensation to Reflect Position and Responsibility and Competitiveness within Industry

        A key component of an executive's total compensation, base salaries are designed to compensate executives commensurate with their respective level of experience, scope of responsibilities, sustained individual performance and future potential. The goal has been to provide for base salaries that are sufficiently competitive with other similar-sized energy companies and/or partnerships, both regionally and nationally, in order to attract and retain talented leaders.