MarkWest Pioneer, L.L.C.

Original Volume No. 1

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Effective Date: 04/01/2009, Docket: RP09-321-000, Status: Effective

MarkWest Pioneer, LLC: Original Volume No. 1

FERC GAS TARIFF

ORIGINAL VOLUME NO. 1

of

MarkWest Pioneer, L.L.C.

filed with the

FEDERAL ENERGY REGULATORY COMMISSION

Communications regarding this Tariff

should be addressed to:

MarkWest Pioneer, L.L.C.

1515 Arapahoe Street

Tower 2, Suite 700

Denver, CO 80202-2126

(303) 925-9200

(303)290-8769 (facsimile)