Markwest Energy Partners L.P.

Frank M. Semple, Chairman, President, and Chief Executive Officer, was appointed as President of both our general partner and MarkWest Hydrocarbon, Inc. on November 1, 2003. Mr. Semple also became Chief Executive Officer of both MarkWest entities on January 1, 2004. Mr. Semple is a member of the Board of Directors of our general partner and was elected Chairman of the Board in October 2008. Prior to his service with MarkWest, Mr. Semple served in various capacities, most recently as Chief Operating Officer of WilTel Communications, formerly Williams Communications Group, Inc. (“WCG”) from 1997 to 2003. Prior to his tenure at WilTel Communications, he was the Senior Vice President/General Manager of Williams Natural Gas from 1995 to 1997, Vice President of Marketing and Vice President of Operations and Engineering for Northwest Pipeline, and Director of Product Movements and Division Manager for Williams Pipeline during his 22-year career with The Williams Companies. During his tenure at Williams Communications, he also served on the board of directors for PowerTel Communications and the Competitive Telecommunications Association (Comptel). Mr. Semple holds a Mechanical Engineering degree from the United States Naval Academy and is a professional engineer registered in the state of Kansas.

John C. Mollenkopf, Senior Vice President, Chief Operations Officer, was appointed as Chief Operations Officer of our general partner in October 2006. Prior to his appointment as COO, Mr. Mollenkopf served as Senior Vice President, Southwest Business Unit, since January 2004 and as Vice President, Business Development since January 2003. Prior to these positions,, he served as Vice President, Michigan Business Unit, of our general partner since its inception in May 2002 and in the same capacity with MarkWest Hydrocarbon since December 2001. Prior to that, Mr. Mollenkopf was General Manager of the Michigan Business Unit of MarkWest Hydrocarbon since 1997. He joined MarkWest Hydrocarbon in 1996 as Manager, New Projects. From 1983 to 1996, Mr. Mollenkopf worked for ARCO Oil and Gas Company, holding various positions in process and project engineering, as well as operations supervision.

C. Corwin Bromley, Senior Vice President, General Counsel and Secretary, was appointed as General Counsel of our general partner in September 2004. Prior to joining MarkWest, Mr. Bromley served as Assistant General Counsel at Foundation Coal Holdings, Inc. f/k/a RAG American Coal Holding, Inc. from 1999 through 2004, and as General-Managing Attorney and Sr. Environmental Attorney at Cyprus Amax Minerals Company from 1989 to 1999. Prior to that, Mr. Bromley was in private practice with the law firm Popham, Haik, Schnobrich & Kaufman from 1984 through 1989. Preceding his legal career, Mr. Bromley worked as a structural/design engineer involved in several domestic and international LNG and energy projects with the firms CBI, Inc. and Chicago Bridge & Iron Company. Mr. Bromley received his J.D. degree from the University of Denver and his bachelor’s degree in Civil Engineering from the University of Wyoming.

Andrew L. Schroeder, Vice President Finance, Treasurer and Assistant Secretary, was appointed as Vice President and Treasurer of our general partner in February 2003. Prior to his appointment, he was Director of Finance/Business Development at Crestone Energy Ventures from 2001 through 2002. Prior to that, Mr. Schroeder worked at Xcel Energy for two years as Director of Corporate Financial Analysis. Prior to that, he spent seven years working with various energy companies. He began his career with Touche, Ross & Co. and spent eight years in public accounting. Mr. Schroeder is a Certified Public Accountant licensed in the state of Colorado.

Charles K. Dempster has served as a member of the Board of Directors of our General Partner since December 2002. Mr. Dempster serves as the chairman of the Board’s Compensation Committee and also serves on the Board’s Nominating and Corporate Governance Committee. Mr. Dempster has more than 30 years of experience in the natural gas and power industry. He held various management and executive positions with Enron Corporation and its predecessors between 1969 and 1986, focusing on natural gas supply, transmission and distribution. From 1986 through 1992, Mr. Dempster served as President of Reliance Pipeline Company and Executive Vice President of Nicor Oil and Gas Corporation, oil and natural gas midstream and exploration subsidiaries of Nicor Inc. in Chicago. In 1993, he was appointed President of Aquila Energy Corporation, a wholly owned midstream, pipeline and energy trading subsidiary of Utilicorp, Inc. Mr. Dempster retired in 2000 as Chairman and Chief Executive Officer of Aquila Energy Company. Mr. Dempster holds a bachelor’s degree in civil engineering from the University of Houston and attended graduate business school at the University of Nebraska.

Keith E. Bailey has served as a member of the Board of Directors of our General Partner since January 2005. Mr. Bailey serves as the chairman of the Board’s Audit Committee and also serves on the Board’s Finance Committee. Mr. Bailey was formerly the Chairman, President and Chief Executive Officer of The Williams Companies, Inc. (“Williams”). Commencing in 1973, Mr. Bailey served in various capacities with Williams and its subsidiaries, including President and Chairman of Williams Pipe Line, Chairman of WilTel Communications, President of Williams Natural Gas, and Executive Vice President and Chief Financial Officer of Williams. Also, Mr. Bailey served on the Williams Board of Directors from 1988 until his retirement in 2002, including eight years as Chairman. He currently serves on the Boards of Directors of Apco Argentina Inc., Associated Electric & Gas Insurance Services Limited (AEGIS) and Integrys Energy Group, Inc. Mr. Bailey holds a bachelor’s degree in mechanical engineering from the Missouri School of Mines and Metallurgy.

William A. Kellstrom has served as a member of the Board of Directors of our General Partner since its inception in May 2002 and of MarkWest Hydrocarbon’s Board of Directors since May 2000. Mr. Kellstrom serves on the General Partner’s Finance Committee and also serves on the Board’s Compensation Committee. Mr. Kellstrom has held a variety of managerial positions in the natural gas industry since 1968. They include distribution, pipelines and marketing. He held various management and executive positions with Enron Corporation, including Executive Vice President, Pipeline Marketing and Senior Vice President, Interstate Pipelines. In 1989, he created and was President of Tenaska Marketing Ventures, a gas marketing company for the Tenaska Power Group. From 1992 until 1997 he was with NorAm Energy Corporation (since merged with Reliant Energy, Inc.) where he was President of the Energy Marketing Company and Senior Vice President, Corporate Development. Mr. Kellstrom retired in 1997 and is periodically engaged as a consultant to energy companies.

William P. Nicoletti has served as a member of the Board of Directors of our general partner since its inception in May 2002. Mr. Nicoletti serves on the Board’s Audit Committee and also serves on the Board’s Nominating and Corporate Governance Committee. Mr. Nicoletti is Managing Director of Nicoletti & Company Inc., a private banking firm formed in 1991. Previously, he was a Managing Director and head of Energy Investment Banking for PaineWebber Incorporated and E.F Hutton & Company Inc. Mr. Nicoletti is a director and Chairman of the Audit Committee of Kestrel Heat LLC, the general partner of Star Gas Partners, L.P. Mr. Nicoletti is a graduate of Seton Hall University and received an MBA from Columbia University Graduate School of Business.