Markwest Hydrocarbon Inc.

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.

Nancy K. Buese, Senior Vice President, Chief Financial Officer, was appointed Chief Financial Officer of our general partner in October 2006. Prior to her appointment as CFO, Ms. Buese served as Chief Accounting Officer of MarkWest since November 2005. Prior to joining MarkWest, Ms. Buese was the Chief Financial Officer for Experimental and Applied Sciences (“EAS”) in Golden, Colorado. EAS is a wholly owned subsidiary of Abbott Laboratories. Prior to her employment at EAS, Ms. Buese was a Vice President with TransMontaigne Inc. in Denver, Colorado. Preceding this appointment, Ms. Buese was a Partner with Ernst & Young LLP, having spent time in the firm’s Denver, London, New York and Washington, D.C. offices.

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.

Anne E. Mounsey was elected to the Board of Directors of our General Partner in February 2008. Ms. Mounsey previously served as a member of the Board of Directors of MarkWest Hydrocarbon, Inc. from October 2004 through February 2008. From 1991 to 2003, Ms. Mounsey held various positions with MarkWest Energy and MarkWest Hydrocarbon, her most recent as Manager of Marketing and Business Development. Ms. Mounsey is the daughter of John M. Fox, our General Partner’s Lead Director.

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.