In accordance with General Instruction B.2 of Form 8-K, the following information in this Current Report on Form 8-K (including the exhibit) is furnished pursuant to Item 7.01 and shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 or otherwise subject to the liabilities of that section. This Current Report will not be deemed an admission as to the materiality of any information in the report that is required to be disclosed solely by Regulation FD.

On October 19, 2009, Frank Semple, Chairman, President & Chief Executive Officer, will present at Hart's Developing Unconventional Gas Conference at the David L. Lawrence Convention Center in Pittsburgh, Pennsylvania. The information included with this Current Report as Exhibit 99.1 includes graphic images or slides that will be made available at this meeting. These slides are available for viewing at our website, www.markwest.com, although we reserve the right to discontinue that availability at any time.

The presentation furnished with this Current Report on Form 8-K utilizes the Non-GAAP financial measures of Distributable Cash Flow and Adjusted EBITDA. In general, we define Distributable Cash Flow as net income attributable to the Partnership adjusted for (i) depreciation, amortization, accretion and impairment expense; (ii) amortization of deferred financing costs,
(iii) non-cash earnings from unconsolidated affiliates; (iv) distributions from (contributions to) unconsolidated affiliates (net of affiliate's growth capital expenditures); (v) non-cash compensation expense; (vi) non-cash derivative activity; (vii) losses (gains) on the disposal of property, plant and equipment ("PP&E"); (viii) provision for deferred income taxes; (ix) adjustments for non-controlling interest in consolidated subsidiaries; (x) losses (gains) relating to other miscellaneous non-cash amounts affecting net income for the period; and (xi) maintenance capital expenditures. We define Adjusted EBITDA as net income attributable to the Partnership adjusted for (i) depreciation, amortization, accretion, and impairment expense; (ii) interest expense;
(iii) amortization of deferred financing costs; (iv) losses (gains) on the disposal of PP&E; (v) non-cash derivative activity; (vi) non-cash compensation expense; (vii) provision for income taxes; (viii) adjustments for non-controlling interest in consolidated subsidiaries; and (ix) losses (gains) relating to other miscellaneous non-cash amounts affecting net income for the period.

Distributable Cash Flow is a financial performance measure used by management as a key component in the determination of cash distributions paid to unitholders. We believe distributable cash flow is an important financial measure for unitholders as an indicator of cash return on investment and to evaluate whether the Partnership is generating sufficient cash flow to support quarterly distributions. In addition, distributable cash flow is commonly used by the investment community because the market value of publicly traded partnerships is based, in part, on distributable cash flow and cash distributions paid to unitholders.

Adjusted EBITDA is a financial performance measure used by management, industry analysts, investors, lenders, and rating agencies to assess the financial performance and operating results of the Partnership's ongoing business operations. Additionally, we believe Adjusted EBITDA provides useful information to investors for trending, analyzing, and benchmarking our operating results from period to period as compared to other companies that may have different financing and capital structures.

Cautionary Statements

This filing includes "forward-looking statements." All statements other than statements of historical facts included or incorporated herein may constitute forward-looking statements. Actual results could vary significantly from those expressed or implied in such statements and are subject to a number of risks and uncertainties. Although we believe that the expectations reflected in the forward-looking statements are reasonable, we can give no assurance that such expectations will prove to be correct. The forward-looking statements involve risks and uncertainties that affect our operations, financial performance, and other factors as discussed in our filings with the Securities and Exchange Commission. Among the factors that could cause results to differ materially are those risks discussed in the periodic reports we file with the SEC, including our Annual Report on Form 10-K, for the year ended December 31, 2008, and our Quarterly Report on Form 10-Q, for the quarterly period ended June 30, 2009, as filed with the SEC. You are urged to carefully review and consider the cautionary statements and other disclosures made in those filings, specifically those under the heading "Risk Factors."

(d) Exhibits.

Exhibit No.                           Description of Exhibit
99.1          Presentation at Hart's Developing Unconventional Gas Conference on
              October 19, 2009.