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): March 20, 2012

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 March 20, 2012, Randy Nickerson, Senior Vice President & Chief Commercial Officer, will present at the Hart’s Marcellus Midstream Conference 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 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, 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	Presentation on March 20, 2012, at the Hart’s Marcellus Midstream Conference in Pittsburgh, Pennsylvania.

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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: March 20, 2012	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

Hart’s Marcellus Midstream Conference Randy Nickerson Senior VP and Chief Commercial Officer March 2012

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, 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

Geographic Footprint UTICA • Joint Venture with EMG • Under construction: • 200 MMcf/d cryogenic processing complex in Harrison County, Ohio • 100,000 Bbl/d fractionation, storage, and marketing complex in Harrison County • Noble County processing complex SOUTHWEST • Granite Wash, Woodford, Cotton Valley, Travis Peak, Haynesville • 1.6 Bcf/d gathering capacity • 655 MMcf/d processing capacity • Arkoma Connector Pipeline JV • Under construction: • 120 MMcf/d cryogenic processing capacity in East Texas 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 • Under construction: • 150 MMcf/d Langley expansion LIBERTY • Marcellus Shale • 325 MMcf/d gathering capacity • 625 MMcf/d cryogenic processing • 60,000 Bbl/d C3+ fractionator • Under construction: • ~1.1 Bcf/d processing capacity • 115,000 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

Growth Driven by Customer Satisfaction 4 MarkWest Ranked #1 in Natural Gas Midstream Services Customer Satisfaction EnergyPoint Research, Inc. 2011 Customer Satisfaction Survey

MarkWest Liberty Marcellus Project Schedule 5 Houston I, II, III Houston Processing and Fractionation Complex Houston I, II, and III 355 MMcf/d C3+ Fractionation 60,000 Bbl/d C3 pipeline TEPPCO Deliveries NGL Storage 1.3 MM Bbls Truck Loading 8 Bays Under Construction Rail Loading (2Q12) 200 Rail cars De-ethanization (mid-2013) ~38,000 Bbl/d Mariner West ethane pipeline (3Q13) 50,000 Bbl/d Majorsville Processing and Fractionation Complex Majorsville I and II 270 MMcf/d NGL Pipeline to Houston Under Construction Majorsville III and IV (2013) 400 MMcf/d De-ethanization (mid-2013) ~38,000 Bbl/d De-ethanization (2014) ~38,000 Bbl/d Mobley Processing Complex Under Construction Mobley I (3Q12) 120 MMcf/d Mobley II (4Q12) 200 MMcf/d NGL Pipeline to Majorsville (2Q12) Sherwood Processing Complex Under Construction Sherwood I (3Q12) 200 MMcf/d Sherwood II (4Q13) 200 MMcf/d Mobley I,II Sherwood I, II Majorsville I,II,III,IV TEPPCO PRODUCTS PIPELINE MARINER WEST EPD ATEX EXPRESS PIPELINE MarkWest Liberty is developing integrated and scalable gathering, processing, fractionation, and marketing infrastructure to support production in excess of 1.7 Bcf/d PROPOSED NGL GATHERING

Houston Processing and Fractionation Complex 6

Majorsville Processing and Fractionation Complex 7

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 • MarkWest Liberty is constructing 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 will increase the capacity to 115,000 Bbl/d of ethane and will be online in 2014 • 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 8

Increasing Demand for US Ethane 9 US Ethylene Industry's Max Capability to Crack Ethane (1000 BPD) 0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 Low Probability New Plants High Probability New Plants Converisons/Expansions/Restarts 2011 C2 Cracking Capability Source: En*Vantage, Industry Contacts

Project Mariner: A Comprehensive Solution 10 MarkWest Houston Fractionator Mariner East Mariner West New MarkWest Liberty Pipeline Existing Sunoco Pipeline Existing Sunoco Pipeline Sarnia Pittsburgh Philadelphia Proposed Shell Ethane Cracker

Mariner East: An Ethane and Propane Solution • Mariner East is a scalable project that can deliver ethane and propane to attractive North America and international NGL markets • Mariner East would transport a mixed E/P stream to Marcus Hook (Philadelphia) where the E/P mix would be fractionated into purity products • Creates a European market for Appalachian ethane and an alternative option for Gulf Coast ethane deliveries. Both options can be expanded as market opportunities mature • Projected propane production from the Marcellus and Utica supports the potential export of propane from the Northeast • Provides new pipeline options for delivering propane into Pennsylvania and New York markets using existing Sunoco pipeline assets • Potential propane exports include Belvieu-based sales to Caribbean and South America markets and naphtha-based sales to European markets 11 Sarnia Pittsburgh Gulf Coast Philadelphia

MarkWest Utica Overview 12 Harrison Processing and Fractionation Complex Under Construction Harrison I (3Q12) 40 MMcf/d Harrison II (1Q13) 125 MMcf/d Harrison III (2013) 200 MMcf/d C3+ Fractionation (4Q13) 60,000 Bbl/d C3 pipeline (4Q13) TEPPCO Deliveries De-ethanization (1Q14) 40,000 Bbl/d Truck Loading (1H13) 8 Bays Rail Loading (1H13) 200 Rail cars Noble Processing Complex Planned Construction Noble I (2012) 10 MMcf/d Noble II (2013) 200 MMcf/d NGL Pipelines Under Construction NGL Pipeline from Harrison to Majorsville (4Q13) NGL Pipeline from Harrison to Noble (4Q13) Mobley Sherwood NGL pipeline TEPPCO Pipeline 200 MMcf/d Harrison processing complex Noble processing complex 100,000 Bbl/d fractionation and marketing facilities Houston Majorsville NGL pipeline Proposed NGL gathering Proposed Shell ethane cracker • Joint venture with The Energy & Minerals Group (EMG) to develop significant midstream infrastructure to serve producers’ drilling programs in the liquids-rich Utica shale in eastern Ohio • EMG will fund the first $500 million of capital expenditures • Competitively positioned • Leverages MarkWest’s significant Marcellus and Appalachian assets, and extensive NGL marketing experience in the Northeast

MarkWest is the Midstream Leader in Northeast Shales 13 Utica Shale Marcellus Shale Huron Shale

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 14