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Employee Benefit Plan	12 Months Ended
Employee Benefit Plan	Dec. 31, 2013
Employee Benefit Plan
Employee Benefit Plan	21. Employee Benefit Plan All employees dedicated to, or otherwise principally supporting the Partnership are employees of MarkWest Hydrocarbon, and substantially all of these employees are participants in MarkWest Hydrocarbon's defined contribution benefit plan. The employer matching contribution expense related to this plan was $4.2 million, $3.2 million and $2.7 million for the years ended December 31, 2013, 2012 and 2011, respectively.