Anne Elizabeth Fox Mounsey

MarkWest Hydrocarbon LLC provides natural gas processing services. It also provides transportation, fractionation, and storage of natural gas liquids and transportation of crude oil. The company was founded by John M. Fox in April 1998 and is headquartered in Denver, CO.

MarkWest Energy Partners LP engages in the business of gathering, processing and transportation of natural gas; the transportation, fractionation, storage and marketing of natural gas liquids; and the gathering and transportation of crude oil. It operates through four segments: Marcellus, Utica, Northeast and Southwest. The Southwest segment includes the operations of processing facilities in Corpus Christi, Texas. The Northeast segment assets include the Kenova, Boldman, Cobb, Kermit and the Langley natural gas processing complexes, NGL pipeline and Siloam NGL fractionation facility. The Marcellus segment includes gathering, processing and fractionation infrastructure in the liquids-rich area of the Marcellus Shale The Utica segment provides fractionation services. The company was founded in January 2002 and is headquartered in Denver, CO.

Part of Marathon Petroleum Corp., MarkWest Energy GP LLC is a private company that provides oil and gas field services not elsewhere classified. The company is based in Englewood, CO. The company was founded by John C. Mollenkopf.