16. Equity

The Partnership Agreement stipulates the circumstances under which the Partnership is authorized to issue new capital, maintain capital accounts and distribute cash and contains specific provisions for the allocation of net income and losses to each of the partners for purposes of maintaining their respective partner capital accounts.

Distributions of Available Cash

The Partnership distributes all of its Available Cash, including the Available Cash of its subsidiaries, to all common unitholders of record within 45 days after the end of each quarter. Available Cash is generally defined as all cash and cash equivalents of the Partnership on hand at the end of each quarter, less reserves established by the general partner for future requirements, plus all cash for the quarter from working capital borrowings made after the end of the quarter. The general partner has the discretion to establish cash reserves that are necessary or appropriate to (i) provide for the proper conduct of the Partnership's business; (ii) comply with applicable law, any debt instruments or other agreements; or (iii) provide funds for distributions to unitholders and the general partner for up to the next four quarters. Class A unitholders receive distributions of Available Cash (excluding the Available Cash attributable to MarkWest Hydrocarbon). However, because all Class A unitholders are wholly-owned subsidiaries, these intercompany distributions do not impact the amount of Available Cash that can be distributed to common unitholders. Class B units are not entitled to participate in any distributions of Available Cash prior to their conversion.

The quarterly cash distributions applicable to 2012, 2011 and 2010 were as follows:

Quarter Ended	Distribution Per Common Unit		Declaration Date	Record Date	Payment Date

December 31, 2012	$	0.82	January 23, 2013	February 6, 2013	February 14, 2013
September 30, 2012	$	0.81	October 25, 2012	November 7, 2012	November 14, 2012
June 30, 2012	$	0.80	July 26, 2012	August 6, 2012	August 14, 2012
March 31, 2012	$	0.79	April 26, 2012	May 7, 2012	May 15, 2012
December 31, 2011	$	0.76	January 26, 2012	February 6, 2012	February 14, 2012
September 30, 2011	$	0.73	October 18, 2011	November 7, 2011	November 14, 2011
June 30, 2011	$	0.70	July 21, 2011	August 1, 2011	August 12, 2011
March 31, 2011	$	0.67	April 21, 2011	May 2, 2011	May 13, 2011
December 31, 2010	$	0.65	January 27, 2011	February 7, 2011	February 14, 2011
September 30, 2010	$	0.64	October 27, 2010	November 8, 2010	November 12, 2010
June 30, 2010	$	0.64	July 22, 2010	August 2, 2010	August 13, 2010
March 31, 2010	$	0.64	April 22, 2010	May 3, 2010	May 14, 2010

Equity Offerings

The public equity offerings completed in 2012, 2011 and 2010 were as follows (in millions):

Closing date of offering		Net proceeds(2)

April 6, 2010	4.9	$	142
January 14, 2011	3.5	$	138
July 13, 2011	4.0	$	185
October 13, 2011	5.8	$	251
December 19, 2011	10.0	$	521
January 13, 2012	0.7	$	38
March 16, 2012	6.8	$	388
May 14, 2012(3)	8.0	$	427
August 17, 2012	6.9	$	338
November 19, 2012	9.8	$	437
December 2012(4)	0.1	$	6

(1): Includes the full exercise of the underwriters' overallotment option unless otherwise noted.
(2): Net proceeds from equity offerings were used to repay borrowings under the Credit Facility, to fund acquisitions and capital expenditures and to provide working capital for general partnership purposes.
(3): The underwriters' did not exercise their over-allotment option for this offering.
(4): In November 2012, the Partnership announced a continuous equity program which allows the Partnership from time to time, through the Manager, as its sales agent, to offer and sell common units representing limited partner interests having an aggregate offering price of up to $600 million. Sales of such common units will be made by means of ordinary brokers' transactions on the NYSE at market prices, in block transactions or as otherwise agreed upon by the Manager and the Partnership. The Partnership may also sell common units to the Manager as principal for its own account at a price to be agreed upon at the time of the sale. For any such sales, the Partnership will enter into a separate agreement with the Manager.