8-K

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT
PURSUANT TO SECTION 13 OR 15(d) OF
THE SECURITIES EXCHANGE ACT OF 1934

Date of Report (Date of earliest event reported): November 17, 2011

MARKWEST ENERGY PARTNERS, L.P.

(Exact name of registrant as specified in its charter)

Delaware (State or other jurisdiction of incorporation or organization) 001-31239 (Commission File Number) 27-0005456 (I.R.S. Employer Identification Number)

1515 Arapahoe Street, Tower 1, Suite 1600, Denver CO 80202

(Address of principal executive offices)

Registrant’s telephone number, including area code: 303-925-9200

Not Applicable.

(Former name or former address, if changed since last report.)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

oWritten Communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

oSoliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

oPre-Commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

oPre-Commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

ITEM 7.01. Regulation FD

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 November 17, 2011, Frank Semple, Chairman, President & Chief Executive Officer, will present at the RBC Capital Markets’ 2011 Conference in Dallas.  The information included with this Current Report as Exhibit 99.1 includes graphic images or slides that will be made available at these meetings.  These slides are available for viewing at our website, www.markwest.com, although we reserve the right to discontinue that availability at any time.

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, 2010, and our Quarterly Report on Form 10-Q for the quarters ended June 30, 2011 and September 30, 2011.  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.”  We do not undertake any duty to update any forward-looking statement except as required by law.

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ITEM 9.01.  Financial Statements and Exhibits.

(d)Exhibits.

Exhibit No.	Description of Exhibit
99.1	Investor Presentation on November 17, 2011

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SIGNATURE

Pursuant to the requirements of the Securities and Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

	MARKWEST ENERGY PARTNERS, L.P.
			(Registrant)
	By:	MarkWest Energy GP, L.L.C.,
		Its General Partner
Date: November 17, 2011	By:	/s/ NANCY K. BUESE
		Nancy K. Buese
		Senior Vice President and Chief Financial Officer

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EX-99.1

Exhibit 99.1

RBC Capital Markets MLP Conference November 2011

Forward-Looking Statements This presentation contains forward-looking statements and information. These forward-looking statements, which in many instances can be identified by words like “could,” “may,” “will,” “should,” “expects,” “plans,” “project,” “anticipates,” “believes,” “planned,” “proposed,” “potential,” and other comparable words, regarding future or contemplated results, performance, transactions, or events, are based on MarkWest Energy Partners, L.P. (“MarkWest” and “Partnership”) current information, expectations and beliefs, concerning future developments and their potential effects on MarkWest. 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, and actual results, performance , distributions , events or transactions could vary significantly from those expressed or implied in such statements and are subject to a number of uncertainties and risks. 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, 2010, and our Quarterly Report on Form 10-Q for the quarter ended September 30, 2011. You are urged to carefully review and consider the cautionary statements and other disclosures, including those under the heading “Risk Factors,” made in those documents. If any of the uncertainties or risks develop into actual events or occurrences, or if underlying assumptions prove incorrect, it could cause actual results to vary significantly from those expressed in the presentation, and our business, financial condition, or results of operations could be materially adversely affected. Key uncertainties and risks that may directly affect MarkWest’s performance, future growth, results of operations, and financial condition, include, but are not limited to: Fluctuations and volatility of natural gas, NGL products, and oil prices; A reduction in natural gas or refinery off-gas production which we gather, transport, process, and/or fractionate; A reduction in the demand for the products we produce and sell; Financial credit risks / failure of customers to satisfy payment or other obligations under our contracts; Effects of our debt and other financial obligations, access to capital, or our future financial or operational flexibility or liquidity; Construction, procurement, and regulatory risks in our development projects; Hurricanes, fires, and other natural and accidental events impacting our operations, and adequate insurance coverage; Terrorist attacks directed at our facilities or related facilities; Changes in and impacts of laws and regulations affecting our operations and risk management strategy; and Failure to integrate recent or future acquisitions. 2

MarkWest Geographic Footprint SOUTHWEST Granite Wash, Woodford, Cotton Valley, Travis Peak, Haynesville 1.6 Bcf/d gathering capacity 655 MMcf/d processing capacity Arkoma Connector Pipeline JV NORTHEAST Huron/Berea Shale 505 MMcf/d processing capacity 24,000 Bbl/d NGL fractionation facility 285,000 barrel propane storage NGL marketing by truck, rail, & barge Infrastructure under construction Langley processing expansion Complete Ranger NGL pipeline LIBERTY Marcellus Shale JV with The Energy & Minerals Group 325 MMcf/d gathering capacity 625 MMcf/d cryogenic processing 60,000 Bbl/d C3+ fractionator Infrastructure under construction 520 MMcf/d processing capacity 75,000 Bbl/d de-ethanization 50,000 Bbl/d Mariner West project GULF COAST 140 MMcf/d cryogenic gas plant processing refinery off-gas 29,000 Bbl/d NGL fractionation capacity NGL marketing and transportation 3

MarkWest Liberty Marcellus Project Schedule 4 Mobley Processing Complex Under Construction Mobley I (2Q12) 120 MMcf/d Mobley II (3Q12) 200 MMcf/d NGL Pipeline to Majorsville (2Q12) Majorsville Processing Complex Majorsville I and II 270 MMcf/d NGL Pipeline to Houston Houston Processing and Fractionation Complex Houston I, II, and III 355 MMcf/d C3+ fractionation 60,000 Bbl/day C3 pipeline TEPPCO deliveries NGL Storage 1.3MM bbls Truck loading 8 bays Under Construction Rail Loading 200 Rail Cars De-ethanization (3Q13) 75,000 Bbl/day Mariner West ethane pipeline (3Q13) 50,000 Bbl/day MarkWest Liberty is developing integrated and scalable gathering, processing, fractionation, and marketing infrastructure to support production in excess of 1 Bcf/d Sherwood Processing Complex Under Construction Sherwood I (3Q12) 200 MMcf/d NGL Pipeline to Mobley (3Q12) TEPPCO PRODUCTS PIPELINE Majorsville I,II Houston I,II,III Mobley I, II Sherwood I MARINER WEST PROPOSED EPD ETHANE PIPELINE PROPOSED MARINER EAST

Significant Forecasted Growth in Cryogenic Processing Capacity MW Liberty Planned Processing Capacity MW Liberty Future Processing Capacity 5

MarkWest Liberty Propane Supply and Distribution 6 MarkWest Liberty has invested significant capital to develop a world-class NGL fractionation, storage, and marketing complex with pipeline, rail, and truck facilities Northeast markets can support significant propane sales from the Marcellus The potential shut-down of Philadelphia-area refiners would have the effect of significantly reducing the propane supply in the Northeast

MarkWest Liberty has the ability to recover ethane at all of its processing plants and to transport the ethane to de-ethanization facilities via its extensive NGL gathering system In September, MarkWest Liberty announced the development of up to three large de-ethanizers at its Houston and Majorsville processing complexes The first phase will have capacity of ~75,000 Bbl/d and will commence operation in mid-2013 to coincide with the start-up of Mariner West The second phase would increase the capacity to more than 115,000 Bbl/d of ethane MarkWest will also construct an ethane pipeline to transport ethane from Majorsville to Houston MarkWest Liberty’s Processing Complexes Support Ethane Recovery MW Liberty Planned Ethane Fractionation Capacity MW Liberty Must Recover Ethane MW Liberty Total Recoverable Ethane 7

Marcellus Ethane – A Third-Party Viewpoint 8 Implied Ethane Production In the Marcellus Based on Processing Capacity Source: Wells Fargo

Project Mariner: A Comprehensive Ethane Solution MarkWest Liberty and Sunoco Logistics are developing efficient and scalable ethane projects that meet producers’ ethane production schedules and provide access to attractive NGL markets in North America and Europe Project Mariner requires minimal pipeline construction – a combined total of approximately 85 miles of new pipe is required to deliver ethane to the Sarnia, Gulf Coast, and European markets Project Mariner will have access to ethane storage at Sarnia and would construct ethane storage at Philadelphia and the Gulf Coast near Nederland, Texas Mariner West is scheduled to come online in mid-2013 for transportation to Sarnia, with potential future ethane deliveries to favorable European and Gulf Coast markets via Mariner East The capacity of Sunoco Logistics’ 8-inch pipeline to Philadelphia can be increased to meet increased demand 9 Sarnia Houston Gulf Coast Philadelphia

1515 Arapahoe Street Tower 1, Suite 1600 Denver, Colorado 80202 Phone: 303-925-9200 Investor Relations: 866-858-0482 Email: investorrelations@markwest.com Website: www.markwest.com 10