MarkWest Energy Partners, L.P. (NYSE: MWE) (“MarkWest” or “the Partnership”) reported an incident at its Houston processing and fractionation complex in Houston, Pennsylvania at approximately 6:00 p.m. (EDT) yesterday. The Houston complex consists of processing plants I, II and III totaling 355 million cubic feet per day (MMcf/d) of capacity and 98,000 barrels per day of ethane and heavier fractionation capacity with associated storage facilities and other related infrastructure. There were no reported injuries and as a precaution, the area was safely and temporarily evacuated. Although MarkWest has not completed a full assessment of all plant equipment, an initial visual assessment of damage indicates that the impact was limited to one component of the plant III facility. The entire complex remains shut down until the assessment is completed. At this time, it appears that no other equipment at the facility was affected. Additionally, there are no apparent signs or evidence of a fire. The complex’s safety control system worked as designed and the two flares at the facility remained in operation throughout the course of this event. MarkWest is working closely with its producer customers and is currently routing some gas through its rich-gas header system to the Majorsville complex in Marshall County, West Virginia. The Majorsville complex currently consists of 870 MMcf/d of processing capacity. MarkWest would like to thank the local first responders and Washington County emergency management personnel who acted quickly and decisively to ensure the public’s safety. MarkWest notified the appropriate government officials and agencies. The area will remain secure until the review is completed. MarkWest Energy Partners, L.P. is a master limited partnership engaged in the gathering, processing and transportation of natural gas; the gathering, transportation, fractionation, storage and marketing of natural gas liquids; and the gathering and transportation of crude oil. MarkWest has a leading presence in many unconventional gas plays including the Marcellus Shale, Utica Shale, Huron/Berea Shale, Haynesville Shale, Woodford Shale and Granite Wash formation.