425

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 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): July 20, 2015

MPLX LP

(Exact name of registrant as specified in its charter)

Delaware	001-35714	45-5010536
(State or other jurisdiction of incorporation)	(Commission File Number)	(IRS Employer Identification Number)

200 E. Hardin Street

Findlay, Ohio 45840

(Address of principal executive offices)

(419) 672-6500

(Registrant’s telephone number, including area code)

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:

x Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

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

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Item 8.01 Regulation FD Disclosure.

On July 20, 2015, MPLX LP (“MPLX”) and MarkWest Energy Partners, L.P. (“MWE”) announced the provision of supplemental information relating to their previously announced entry into a definitive merger agreement pursuant to which MWE would become a wholly owned subsidiary of MPLX. The full text of the press release and the related investor presentation are included as Exhibit 99.1 and Exhibit 99.2, respectively, to this Current Report on Form 8-K and are incorporated into this Item 8.01 by reference.

Additional Information

This communication does not constitute an offer to sell or the solicitation of an offer to buy any securities or a solicitation of any vote or approval. This communication may be deemed to be solicitation material in respect of the proposed transaction. In connection with the proposed transaction, a registration statement on Form S-4 will be filed with the SEC and will include a proxy statement of MWE. INVESTORS AND SECURITY HOLDERS ARE ENCOURAGED TO READ THE REGISTRATION STATEMENT AND ANY OTHER RELEVANT DOCUMENTS FILED WITH THE SEC, INCLUDING THE PROXY STATEMENT/PROSPECTUS THAT WILL BE PART OF THE REGISTRATION STATEMENT, WHEN THEY BECOME AVAILABLE, BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED MERGER. The final proxy statement/prospectus will be mailed to unitholders of MWE. Investors and security holders will be able to obtain the documents free of charge at the SEC’s website, www.sec.gov, from MPLX LP at its website, http://ir.mplx.com, or 200 E. Hardin Street, Findlay, Ohio 45840, Attention: Corporate Secretary, or from MWE at its website, http://investor.markwest.com, or 1515 Arapahoe Street, Tower 1, Suite 1600, Denver, CO 80202, Attention: Corporate Secretary.

Participants in Solicitation

MPLX and MWE and their respective directors and executive officers may be deemed to be participants in the solicitation of proxies in respect of the proposed merger. Information concerning MPLX participants is set forth in MPLX’s Form 10-K for the year ended December 31, 2014, as filed with the SEC on February 27, 2015, and MPLX’s current report on Form 8-K, as filed with the SEC on March 9, 2015. Information concerning MWE’s participants is set forth in the proxy statement, dated April 23, 2015, for MWE’s 2015 Annual Meeting of Common Unitholders as filed with the SEC on Schedule 14A and MWE’s current reports on Form 8-K, as filed with the SEC on May 5, 2015, May 19, 2015 and June 8, 2015. Additional information regarding the interests of participants of MPLX and MWE in the solicitation of proxies in respect of the proposed merger will be included in the registration statement and proxy statement/prospectus and other relevant materials to be filed with the SEC when they become available. These documents, when available, may be obtained free of charge from MPLX or MWE using the contact information above.

SAFE HARBOR FOR FORWARD-LOOKING STATEMENTS

This document contains forward-looking statements within the meaning of federal securities laws regarding MPLX LP (“MPLX”), Marathon Petroleum Corporation (“MPC”), and MarkWest Energy Partners, L.P. (“MWE”). These forward-looking statements relate to, among other things, expectations, estimates and projections concerning the business and operations of MPC, MPLX and MWE. You can identify forward-looking statements by words such as “anticipate,” “believe,” “commit,” “imply,” “estimate,” “objective,” “expect,” “forecast,” “plan,” “project,” “potential,” “could,” “may,” “should,” “would,” “will” or other similar expressions that convey the uncertainty of future events or outcomes. Such forward-looking statements are not guarantees of future performance and are subject to risks, uncertainties and other factors, some of which are beyond the

companies’ control and are difficult to predict. Factors that could cause MPLX’s or MWE’s actual results to differ materially from those in the forward-looking statements include: their ability to complete the proposed merger of MPLX and MWE on anticipated terms and timetable; the ability to obtain approval of the transaction by the unitholders of MWE and satisfy other conditions to the closing of the transaction contemplated by the merger agreement; the ability to obtain governmental approvals of the MPLX/MWE transaction based on the proposed terms and schedule, and any conditions imposed on the combined company in connection with consummation of the MPLX/MWE transaction; the risk that the costs savings and any other synergies from the MPLX/MWE transaction may not be fully realized or may take longer to realize than expected; disruption from the MPLX/MWE transaction making it more difficult to maintain relationships with customers, employees or suppliers; risks relating to any unforeseen liabilities of MWE or MPLX, as applicable; the adequacy of their respective capital resources and liquidity, including, but not limited to, availability of sufficient cash flow to pay distributions and execute their respective business plans; the timing and extent of changes in commodity prices and demand for crude oil, refined products, feedstocks or other hydrocarbon-based products; volatility in and/or degradation of market and industry conditions; completion of pipeline capacity by competitors; disruptions due to equipment interruption or failure, including electrical shortages and power grid failures; the suspension, reduction or termination of MPC’s obligations under MPLX’s commercial agreements; each company’s ability to successfully implement its growth plan, whether through organic growth or acquisitions; modifications to earnings and distribution growth objectives; federal and state environmental, economic, health and safety, energy and other policies and regulations; changes to MPLX’s capital budget; other risk factors inherent to their industry; and the factors set forth under the heading “Risk Factors” in MPLX’s Annual Report on Form 10-K for the year ended Dec. 31, 2014, filed with the Securities and Exchange Commission (“SEC”); and the factors set forth under the heading “Risk Factors” in MWE’s Annual Report on Form 10-K for the year ended Dec. 31, 2014, filed with the SEC. Factors that could cause MPC’s actual results to differ materially from those in the forward-looking statements include: risks described above relating to the MPLX/MWE proposed merger; changes to the expected construction costs and timing of pipeline projects; volatility in and/or degradation of market and industry conditions; the availability and pricing of crude oil and other feedstocks; slower growth in domestic and Canadian crude supply; an easing or lifting of the U.S. crude oil export ban; completion of pipeline capacity to areas outside the U.S. Midwest; consumer demand for refined products; transportation logistics; the reliability of processing units and other equipment; MPC’s ability to successfully implement growth opportunities; modifications to MPLX earnings and distribution growth objectives; federal and state environmental, economic, health and safety, energy and other policies and regulations; MPC’s ability to successfully integrate the acquired Hess retail operations and achieve the strategic and other expected objectives relating to the acquisition; changes to MPC’s capital budget; other risk factors inherent to MPC’s industry; and the factors set forth under the heading “Risk Factors” in MPC’s Annual Report on Form 10-K for the year ended Dec. 31, 2014, filed with SEC. In addition, the forward-looking statements included herein could be affected by general domestic and international economic and political conditions. Unpredictable or unknown factors not discussed here, in MPLX’s Form 10-K, in MPC’s Form 10-K or in MWE’s Form 10-K could also have material adverse effects on forward-looking statements. Copies of MPLX’s Form 10-K are available on the SEC website, MPLX’s website at http://ir.mplx.com or by contacting MPLX’s Investor Relations office. Copies of MPC’s Form 10-K are available on the SEC website, MPC’s website at http://ir.marathonpetroleum.com or by contacting MPC’s Investor Relations Office. Copies of MWE’s Form 10-K are available on the SEC website, MWE’s website at http://investor.markwest.com or by contacting MWE’s Investor Relations office.

None of MPLX, MPC or MWE undertake any duty to update any forward-looking statement except as required by law.

Item 9.01 Financial Statements and Exhibits.

See the Exhibit Index set forth below for a list of exhibits included with this Form 8-K.

Exhibit Number	Description
99.1	Press Release dated July 20, 2015.
99.2	Investor Presentation dated July 20, 2015.

SIGNATURES

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

		MPLX LP
	By:	MPLX GP LLC, its General Partner
Date: July 20, 2015
	By:	/s/ J. Michael Wilder
	Name: Title:	J. Michael Wilder Vice President, General Counsel and Secretary

EXHIBIT INDEX

Exhibit Number	Description
99.1	Press Release dated July 20, 2015.
99.2	Investor Presentation dated July 20, 2015.

EX-99.1

Exhibit 99.1

MPLX & MarkWest provide supplemental information regarding the strategic combination announced July 13

FINDLAY, Ohio, and DENVER, July 20, 2015 – Last week MPLX LP (NYSE: MPLX) and MarkWest Energy Partners, L.P. (NYSE:MWE) (MarkWest) announced they had signed a definitive merger agreement whereby MarkWest would become a wholly owned subsidiary of MPLX. In connection with the announcement, MPLX affirmed its anticipated distribution growth guidance of 29 percent in 2015 and shared that it expects a 25 percent compound annual distribution growth rate for the combined entity through 2017, with a “peer-leading” distribution growth profile thereafter. MPLX and MarkWest are clarifying “peer-leading” implies an annual distribution growth profile of approximately 20 percent in years 2018 and 2019.

The combined partnership also anticipates the opportunity for incremental growth capital investments afforded by the stronger financial position of the combined entity and support from its investment grade sponsor Marathon Petroleum Corporation (NYSE:MPC).

MPLX and MarkWest are providing additional information on the incremental organic growth opportunities available to the combined partnership, and have added information to the announcement materials to supplement that discussion.

All materials will be available under the Investor Relations tabs for MPLX at http://www.mplx.com and MarkWest at http://www.markwest.com and will be a part of a Form 8-K filed with the Securities Exchange Commission this morning.

###

About MPLX LP

MPLX is a fee-based, growth-oriented master limited partnership formed in 2012 by Marathon Petroleum Corporation to own, operate, develop and acquire pipelines and other midstream assets related to the transportation and storage of crude oil, refined products and other hydrocarbon-based products. Headquartered in Findlay, Ohio, MPLX’s assets consist of a 99.5 percent equity interest in a network of common carrier crude oil and products pipeline assets located in the Midwest and Gulf Coast regions of the United States and a 100 percent interest in a butane storage cavern located in West Virginia with approximately 1 million barrels of natural gas liquids storage capacity.

About MarkWest Energy Partners

MarkWest Energy Partners, L.P. is a master limited partnership that owns and operates midstream service businesses. MarkWest has a leading presence in many natural gas resource plays including the Marcellus Shale, Utica Shale, Huron/Berea Shale, Haynesville Shale, Woodford Shale and Granite Wash formation.

MPLX Investor Relations Contacts:

Geri Ewing (419) 421-2071

Teresa Homan (419) 421-2965

MPLX Media Contacts:

Chuck Rice (419) 421-2521

Jamal Kheiry (419) 421-3312

MarkWest Investor Relations and Media Contact:

Joshua Hallenbeck (866) 858-0482

This press release contains forward-looking statements within the meaning of federal securities laws regarding MPLX LP (“MPLX”), Marathon Petroleum Corporation (“MPC”), and MarkWest Energy Partners, L.P. (“MWE”). These forward-looking statements relate to, among other things, expectations, estimates and projections concerning the business and operations of MPC, MPLX and MWE. You can identify forward-looking statements by words such as “anticipate,” “believe,” “imply,” “estimate,” “objective,” “expect,” “forecast,” “plan,” “project,” “potential,” “could,” “may,” “should,” “would,” “will” or other similar expressions that convey the uncertainty of future events or outcomes. Such forward-looking statements are not guarantees of future performance and are subject to risks, uncertainties and other factors, some of which are beyond the companies’ control and are difficult to predict. Factors that could cause MPLX’s or MWE’s actual results to differ materially from those in the forward-looking statements include: their ability to complete the proposed merger of MPLX and MWE on anticipated terms and timetable; the ability to obtain approval of the transaction by the unitholders of MWE and satisfy other conditions to the closing of the transaction contemplated by the merger agreement; the ability to obtain governmental approvals of the MPLX/MWE transaction based on the proposed terms and schedule, and any conditions imposed on the combined company in connection with consummation of the MPLX/MWE transaction; the risk that the costs savings and any other synergies from the MPLX/MWE transaction may not be fully realized or may take longer to realize than expected; disruption from the MPLX/MWE transaction making it more difficult to maintain relationships with customers, employees or suppliers; risks relating to any unforeseen liabilities of MWE or MPLX, as applicable; the adequacy of their respective capital resources and liquidity, including, but not limited to, availability of sufficient cash flow to pay distributions and execute their respective business plans; the timing and extent of changes in commodity prices and demand for crude oil, refined products, feedstocks or other hydrocarbon-based products; volatility in and/or degradation of market and industry conditions; completion of pipeline capacity by competitors; disruptions due to equipment interruption or failure, including electrical shortages and power grid failures; the suspension, reduction or termination of MPC’s obligations under MPLX’s commercial agreements; each company’s ability to successfully implement its growth plan, whether through organic growth or acquisitions; modifications to earnings and distribution growth objectives; federal and state environmental, economic, health and safety, energy and other policies and regulations; changes to MPLX’s capital budget; other risk factors inherent to their industry; and the factors set forth under the heading “Risk Factors” in MPLX’s Annual Report on Form 10-K for the year ended Dec. 31, 2014, filed with the Securities and Exchange Commission (SEC); and the factors set forth under the heading “Risk Factors” in MWE’s Annual Report on Form 10-K for the year ended Dec. 31, 2014, filed with the SEC.

2

Factors that could cause MPC’s actual results to differ materially from those in the forward-looking statements include: risks described above relating to the MPLX/MWE proposed merger; changes to the expected construction costs and timing of pipeline projects; volatility in and/or degradation of market and industry conditions; the availability and pricing of crude oil and other feedstocks; slower growth in domestic and Canadian crude supply; an easing or lifting of the U.S. crude oil export ban; completion of pipeline capacity to areas outside the U.S. Midwest; consumer demand for refined products; transportation logistics; the reliability of processing units and other equipment; MPC’s ability to successfully implement growth opportunities; modifications to MPLX earnings and distribution growth objectives; federal and state environmental, economic, health and safety, energy and other policies and regulations; MPC’s ability to successfully integrate the acquired Hess retail operations and achieve the strategic and other expected objectives relating to the acquisition; changes to MPC’s capital budget; other risk factors inherent to MPC’s industry; and the factors set forth under the heading “Risk Factors” in MPC’s Annual Report on Form 10-K for the year ended Dec. 31, 2014, filed with SEC. In addition, the forward-looking statements included herein could be affected by general domestic and international economic and political conditions. Unpredictable or unknown factors not discussed here, in MPLX’s Form 10-K, in MPC’s Form 10-K, or in MWE’s Form 10-K could also have material adverse effects on forward-looking statements. Copies of MPLX’s Form 10-K are available on the SEC website, MPLX’s website at http://ir.mplx.com or by contacting MPLX’s Investor Relations office. Copies of MPC’s Form 10-K are available on the SEC website, MPC’s website at http://ir.marathonpetroleum.com or by contacting MPC’s Investor Relations office. Copies of MWE’s Form 10-K are available on the SEC website, MWE’s website at http://investor.markwest.com or by contacting MWE’s Investor Relations office.

None of MPLX, MPC, or MWE undertake any duty to update any forward-looking statement except as required by law.

Additional Information

This communication may be deemed to be solicitation material in respect of the proposed transaction. In connection with the proposed transaction, a registration statement on Form S-4 will be filed with the SEC and will include a proxy statement of MWE. INVESTORS AND SECURITY HOLDERS ARE ENCOURAGED TO READ THE REGISTRATION STATEMENT AND ANY OTHER RELEVANT DOCUMENTS FILED WITH THE SEC, INCLUDING THE PROXY STATEMENT/PROSPECTUS THAT WILL BE PART OF THE REGISTRATION STATEMENT, WHEN THEY BECOME AVAILABLE, BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED MERGER. The final proxy statement/prospectus will be mailed to unitholders of MWE. Investors and security holders will be able to obtain the documents free of charge at the SEC’s website, www.sec.gov, from MPLX LP at its website, http://ir.mplx.com, or 200 E. Hardin Street, Findlay, Ohio 45840, Attention: Corporate Secretary, or from MWE at its website, http://investor.markwest.com, or 1515 Arapahoe Street, Tower 1, Suite 1600, Denver, CO 80202, Attention: Corporate Secretary.

Participants in Solicitation

MPLX and MWE and their respective directors and executive officers may be deemed to be participants in the solicitation of proxies in respect of the proposed merger. Information concerning MPLX participants is set forth in MPLX’s Form 10-K for the year ended December 31, 2014, as filed with the SEC on February 27, 2015, and MPLX’s current report on Form 8-K, as filed with the SEC on March 9, 2015.

3

Information concerning MWE’s participants is set forth in the proxy statement, dated April 23, 2015, for MWE’s 2015 Annual Meeting of Common Unitholders as filed with the SEC on Schedule 14A and MWE’s current reports on Form 8-K, as filed with the SEC on May 5, 2015, May 19, 2015 and June 8, 2015. Additional information regarding the interests of participants of MPLX and MWE in the solicitation of proxies in respect of the proposed merger will be included in the registration statement and proxy statement/prospectus and other relevant materials to be filed with the SEC when they become available. These documents, when available, may be obtained free of charge from MPLX or MWE using the contact information above.

Non-Solicitation

This communication shall not constitute an offer to sell or the solicitation of an offer to sell or the solicitation of an offer to buy any securities, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. No offer of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the Securities Act of 1933, as amended.

4

EX-99.2

MPLX and MarkWest

Strategic Combination

As Revised

July 20, 2015

Exhibit 99.2

2

This presentation contains forward-looking statements within the meaning of federal securities laws regarding MPLX LP (“MPLX”), Marathon Petroleum Corporation

(“MPC”), and MarkWest Energy Partners, L.P. (“MWE”). These forward-looking statements relate to, among other things, expectations, estimates and projections

concerning the business and operations of MPC, MPLX and MWE. You can identify forward-looking statements by words such as “anticipate,” “believe,” “commit,”

“ imply,” “estimate,” "objective," “expect,” “forecast,” "plan," “project,” "potential," “could,” “may,” “should,” “would,” “will” or other similar expressions that convey the

uncertainty of future events or outcomes. Such forward-looking statements are not guarantees of future performance and are subject to risks, uncertainties and other

factors, some of which are beyond the companies’ control and are difficult to predict. Factors that could cause MPLX's or MWE’s actual results to differ materially from

those in the forward-looking statements include: their ability to complete the proposed merger of MPLX and MWE on anticipated terms and timetable; the ability to obtain

approval of the transaction by the unitholders of MWE and satisfy other conditions to the closing of the transaction contemplated by the merger agreement; the ability to

obtain governmental approvals of the MPLX/MWE transaction based on the proposed terms and schedule, and any conditions imposed on the combined company in

connection with consummation of the MPLX/MWE transaction; the risk that the costs savings and any other synergies from the MPLX/MWE transaction may not be fully

realized or may take longer to realize than expected; disruption from the MPLX/MWE transaction making it more difficult to maintain relationships with customers,

employees or suppliers; risks relating to any unforeseen liabilities of MWE or MPLX, as applicable; the adequacy of their respective capital resources and liquidity,

including, but not limited to, availability of sufficient cash flow to pay distributions and execute their respective business plans; the timing and extent of changes in

commodity prices and demand for crude oil, refined products, feedstocks or other hydrocarbon-based products; volatility in and/or degradation of market and industry

conditions; completion of pipeline capacity by competitors; disruptions due to equipment interruption or failure, including electrical shortages and power grid failures; the

suspension, reduction or termination of MPC's obligations under MPLX’s commercial agreements; each company’s ability to successfully implement its growth plan,

whether through organic growth or acquisitions; modifications to earnings and distribution growth objectives; federal and state environmental, economic, health and

safety, energy and other policies and regulations; changes to MPLX’s capital budget; other risk factors inherent to their industry; and the factors set forth under the

heading "Risk Factors" in MPLX's Annual Report on Form 10-K for the year ended Dec. 31, 2014, filed with the Securities and Exchange Commission (SEC); and the

factors set forth under the heading "Risk Factors" in MWE's Annual Report on Form 10-K for the year ended Dec. 31, 2014, filed with the SEC. Factors that could cause

MPC’s actual results to differ materially from those in the forward-looking statements include: risks described above relating to the MPLX/MWE proposed merger;

changes to the expected construction costs and timing of pipeline projects; volatility in and/or degradation of market and industry conditions; the availability and pricing of

crude oil and other feedstocks; slower growth in domestic and Canadian crude supply; an easing or lifting of the U.S. crude oil export ban; completion of pipeline

capacity to areas outside the U.S. Midwest; consumer demand for refined products; transportation logistics; the reliability of processing units and other equipment;

MPC’s ability to successfully implement growth opportunities; modifications to MPLX earnings and distribution growth objectives; federal and state environmental,

economic, health and safety, energy and other policies and regulations; MPC’s ability to successfully integrate the acquired Hess retail operations and achieve the

strategic and other expected objectives relating to the acquisition; changes to MPC’s capital budget; other risk factors inherent to MPC’s industry; and the factors set

forth under the heading "Risk Factors" in MPC's Annual Report on Form 10-K for the year ended Dec. 31, 2014, filed with SEC. In addition, the forward-looking

statements included herein could be affected by general domestic and international economic and political conditions. Unpredictable or unknown factors not discussed

here, in MPLX’s Form 10-K, in MPC’s Form 10-K, or in MWE’s Form 10-K could also have material adverse effects on forward-looking statements. Copies of MPLX's

Form 10-K are available on the SEC website, MPLX's website at http://ir.mplx.com or by contacting MPLX's Investor Relations office. Copies of MPC's Form 10-K are

available on the SEC website, MPC's website at http://ir.marathonpetroleum.com or by contacting MPC's Investor Relations Office. Copies of MWE’s Form 10-K are

available on the SEC website, MWE’s website at http://investor.markwest.com or by contacting MWE’s Investor Relations office.

None of MPLX, MPC, or MWE undertake any duty to update any forward-looking statement except as required by law.

Forward-Looking Statements

Additional Information

3

Non-GAAP Financial Measures

Adjusted EBITDA and Net Operating Margin are non-GAAP financial measures provided in this presentation. Reconciliation to the nearest GAAP financial

measure is included in the Appendix to this presentation. Adjusted EBITDA is not defined by GAAP and should not be considered in isolation or as an alternative

to net income or other financial measures prepared in accordance with GAAP.

Additional Information

This communication may be deemed to be solicitation material in respect of the proposed transaction.  In connection with the proposed transaction, a registration

statement on Form S-4 will be filed with the SEC and will include a proxy statement of MARKWEST ENERGY PARTNERS, L.P. (“MWE”).  INVESTORS AND

SECURITY HOLDERS ARE ENCOURAGED TO READ THE REGISTRATION STATEMENT AND ANY OTHER RELEVANT DOCUMENTS FILED WITH THE

SEC, INCLUDING THE PROXY STATEMENT/PROSPECTUS THAT WILL BE PART OF THE REGISTRATION STATEMENT, WHEN THEY BECOME

AVAILABLE, BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED MERGER. The final proxy statement/prospectus will be

mailed to unitholders of MWE.  Investors and security holders will be able to obtain the documents free of charge at the SEC’s website, www.sec.gov, from MPLX

LP at its website, http://ir.mplx.com, or 200 E. Hardin Street, Findlay, Ohio 45840, Attention: Corporate Secretary, or from MWE at its website,

http://investor.markwest.com, or 1515 Arapahoe Street, Tower 1, Suite 1600, Denver, CO 80202, Attention: Corporate Secretary.

Participants in Solicitation

MPLX and MWE and their respective directors and executive officers may be deemed to be participants in the solicitation of proxies in respect of the proposed

merger. Information concerning MPLX participants is set forth in MPLX’s Form 10-K for the year ended December 31, 2014, as filed with the SEC on February 27,

2015, and MPLX’s current report on Form 8-K, as filed with the SEC on March 9, 2015. Information concerning MWE’s participants is set forth in the proxy

statement, dated April 23, 2015, for MWE’s 2015 Annual Meeting of Common Unitholders as filed with the SEC on Schedule 14A and MWE’s current reports on

Form 8-K, as filed with the SEC on May 5, 2015, May 19, 2015 and June 8, 2015. Additional information regarding the interests of participants of MPLX and MWE

in the solicitation of proxies in respect of the proposed merger will be included in the registration statement and proxy statement/prospectus and other relevant

materials to be filed with the SEC when they become available.  These documents, when available, may be obtained free of charge from MPLX or MWE using the

contact information above.

Non-Solicitation 

This communication shall not constitute an offer to sell or the solicitation of an offer to sell or the solicitation of an offer to buy any securities, nor shall there be any

sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any

such jurisdiction.  No offer of securities shall be made except by means of a prospectus meeting the requirements of Section 10 of the Securities Act of 1933, as

amended.

Summary of Supplemental Information

Slide 5, 10, 20:  Updates distribution growth targets for 2018 and 2019

–

Combined

partnership

expects

compound

annual

distribution

growth

rate

of

25%

through 2017 and approximately 20% annual distribution growth in years 2018 and

2019

Slide 12-15:  Additional information on growth opportunities

–

MWE

projects

~$1.5

B

annual

baseline

capital

spending

for

the

next

five

years,

with

incremental capital investment of $6 B to $9 B which includes upside growth and

synergistic growth opportunities

4

Powerful Strategic Combination

Creates a large-cap, diversified MLP with a very attractive distribution growth

profile for an extended period of time

–

MPLX affirms 2015 anticipated distribution growth guidance of 29%

–

Combined

partnership

expects

compound

annual

distribution

growth

rate

of

25%

through 2017 and approximately 20% annual distribution growth in years 2018 and

2019

MPC, as the GP sponsor, has interests aligned with the combined MLP and is

committed to provide support for the distribution growth objectives

Significant joint growth opportunities

Substantial benefits for MWE, MPLX and MPC equity owners

–

Attractive premium for MWE unitholders

–

MPLX

unit

exchange

and

the

$3.37

1

per

unit

cash

payment

equalizes

MWE

forecasted distribution for approximately three years

–

Combines MWE's robust organic growth opportunities with MPC’s financial strength

Committed to investment grade credit profile for combined partnership

MWE’s management brings a proven track record of executing organic growth

projects and developing strong customer relationships

5

Notes:

1

$3.37 cash consideration per MWE unit calculated on approximately 200.1 MM fully-diluted MWE common units outstanding, including approximately 8 MM MWE Class B units, outstanding as of 7/10/15. The

cash consideration of $675 MM is a fixed amount and will not increase as additional units are issued by MWE between announcement and closing

Transaction Structure and Terms

Merger

Consideration

Other

Transaction

Structure

MWE common unitholders

will receive 1.09 MPLX common units for each MWE common unit

–

MWE’s ~8 MM Class B units will convert to ~8 MM newly-created MPLX Class B units with

substantially

equivalent

rights

1

MPC will contribute $675 MM of cash, or approximately $3.37 per MWE unit, to MPLX to be paid to

MWE common and Class B unitholders

as additional consideration

2

Implies total consideration of $78.64 per MWE unit, or a 32% premium based on 7/10/15 closing

price of MPLX units

MPLX will assume all of MWE’s cash and the ~$4.2 B of debt outstanding at closing

Two MWE representatives to be added to MPLX board; one MWE representative to be added to

MPC board

Subject to MWE unitholder vote

Subject to regulatory approval and other customary conditions

Expected to close in Q4'15

Combination of MWE and MPLX in a generally tax-free unit-for-unit transaction, plus a one-time

cash payment to MWE unitholders

Fixed exchange ratio

Pro Forma

Ownership

MPC retains control through continued 2% ownership of GP interest

MPC ~21%, MPLX unitholders ~8%, MWE unitholders ~71%

Notes:

1

Convertible in 2016 and 2017 at a ratio of 1.09 MPLX common units for each Class B unit

2

$3.37 cash consideration per MWE unit calculated on approximately 200.1 MM fully-diluted MWE common units outstanding, including approximately 8 MM MWE Class B units, outstanding as of 7/10/15. The

cash consideration of $675 MM is a fixed amount and will not increase as additional units are issued by MWE between announcement and closing

Pro Forma

Leverage

Target leverage of ~4x Debt / Adjusted EBITDA

MPLX will be managed to support an investment grade credit profile

6

Pro Forma Organizational Structure

MWE will operate as a

standalone business within

MPLX:

–

Existing MWE leadership will

become executive officers at

MPLX in roles similar to current

responsibilities

–

MWE will remain operator of

natural gas / NGL platform, which

maintains existing customer

relationships

–

Offices in Denver will remain

–

MPLX board to be expanded to

include two MWE representatives,

including Frank Semple

Pro Forma Organizational Structure

7

Public

Gathering, Processing,

Fractionation & NGL

Transportation

Crude & Refined Product

Transportation &

Logistics

MPLX

19% LP

2% GP / IDR

MPC

MWE Has the Premier Position in Marcellus / Utica

Second largest natural gas processor

and the fourth largest fractionator of

NGLs in the U.S.

Extensive long-term producer

partnerships with Marcellus & Utica

area dedications of 7.7 million acres

Processes and fractionates

approximately three quarters of

growing production from rich-gas

areas in the Northeast

Operates 34 processing and

fractionation facilities in the Marcellus

& Utica shales and has 18 additional

facilities currently under construction

–

7 of the top 10 processing complexes

will be owned by MWE in 2017*

–

8 of the top 14 fractionation complexes

will be owned by MWE in 2017*

8

* Source: Bentek Energy -NGL Facilities Databank as of 5.20.2015

Growth Driven by Customer Satisfaction

MarkWest has received the #1 rating for total customer satisfaction in every

EnergyPoint Research survey since its inception in 2006

9

Pro forma MPLX

–

Best-in-Class Large Cap MLP

379 MBbl/d

fractionation

capacity

6.8 Bcf/d

processing capacity

~7,600 miles of pipelines

MPLX affirms anticipated distribution growth of 29% for

2015

Combined partnership expects distribution growth rate of

25% through 2017

and approximately 20% annual

distribution growth in years 2018 and 2019

Strong sponsor with drop-down portfolio of $1.6 B EBITDA

to support distribution growth

Complementary assets and footprint to provide significant

additional growth opportunities

Large-Cap

MLP

Diversified

and Stable

Cash Flows

Top-Tier

Growth

Profile

Strategic

Sponsor

MPC is a Fortune 25 company with a $35 B enterprise value

Investment grade rated with significant access to low cost of funding

2015E Adjusted EBITDA

2

Market Capitalization

2014A

–

2017E

Distribution

CAGR

2

1.7 MMBbl/d

refining capacity

5,400 miles of pipe

Marine assets

Terminals / railcars

Fuel distribution

MPLX Pro Forma

MPC

> 90% Fee-

Based

2015E

Net

Operating

Margin

3

10

Notes:

1

Reflects MPLX at market price of $69.05 as of 7/10/15 and MWE at estimated transaction value less $675 MM cash component

2

Peer information based on FactSet estimates.  Pro forma MPLX Adjusted EBITDA of $1.25 B represents pro forma Adjusted EBITDA based on midpoint of management guidance range. Pro forma MPLX 2014A

–

2017E distribution CAGR based on management guidance

3

Non-GAAP measure calculated as segment revenue less purchased product costs

$5.5

$5.4

$4.3

$2.4

$1.7

$1.7

$1.5

$1.25

$0

$2

$4

$6

ETP

EPD

WPZ

PAA

EEP

SEP

OKS

PF MPLX

$61

$29

$26

$21

$17

$14

$14

$9

$0

$25

$50

$75

EPD

WPZ

ETP

PF MPLX¹

PAA

EEP

SEP

OKS

14%

8%

7%

7%

6%

5%

3%

0%

10%

20%

30%

PF MPLX

WPZ

SEP

ETP

PAA

EPD

EEP

OKS

Fee-Based

POP / POL

Keep-Whole

Strategic Geographic Footprint

MPC Refineries

MPC Owned and Part-Owned

Third Party

Asphalt/Heavy Oil Terminals

Coastal

Inland

Pipelines

MPC Owned and Operated

MPC Interest: Operated by MPC

MPC Interest: Operated by Others

Pipelines Used by MPC

Light Product Terminals

MPC Owned

Third Party

Water Supplied Terminals

Ethanol Facility

Biodiesel Facility

MarkWest

Southwest

Complex

MarkWest

Northeast

Complex

MarkWest

Marcellus

Complex

MarkWest

Offices

MarkWest

Utica

Complex

MPLX Headquarters (Findlay, OH)

Tank Farms

Butane Cavern

Barge Dock

Products Pipelines

Crude Oil Pipelines

11

Significant Joint Growth Opportunities

Complementary

Integration

Potential for

Additional

Basin

Diversification

Leverages the combined assets and collective expertise

–

Gas processing / fractionation

–

Stabilizers, splitters, pipelines, terminals, trucks, barges and refineries

Strategic opportunity to create new high value products in the Marcellus and

Utica shales

Significant synergies and critical mass to deliver NGLs and refined products

to East Coast markets

MPC’s financial strength and ability to incubate projects facilitates

acceleration of MWE’s existing and future growth

MWE projects ~$1.5 B per year in organic capital spending for the next five

years, with incremental capital investment of $6 B to $9 B which includes

upside growth and synergistic growth opportunities

Enhanced ability to pursue bolt-on or large scale acquisitions as

opportunities arise

Larger entity is better suited to apply core competencies in other basins and

to grow in the Southwest

Positions MPLX as the "first mover" in emerging shale plays

Acceleration

of MWE's

Core Platform

Development

12

MarkWest’s Premier Position Drives ~$1.5 B of Annual

Investment Opportunity

13

Denver Office

Tulsa Office

Canonsburg Office

Cadiz Office

Houston

Office

Area Dedications: 1.4 million acres

Volume Protection: 10% of 2015 capacity

contains minimum volume commitments

Investment Opportunities:

Expansion of gathering and processing

infrastructure to support STACK,

SCOOP, and Springer Shale in Cana-

Woodford

Continued expansion of East Texas

gathering & processing to support

rich-gas areas of  Haynesville Shale

Greenfield development of midstream

system in Permian/Delaware Basin

Volume Protection: 30% of 2015 capacity

contains minimum volume commitments

Area Dedications:  4 million acres

Volume Protection: 70% of 2015 capacity contains

minimum volume commitments

Investment Opportunities:

Expansion of rich-gas gathering systems

Development of additional processing & fractionation

infrastructure (14 facilities currently under construction)

Expansion of NGL pipeline and transportation network

Northeast

Southwest

Marcellus

Utica

Area Dedications:  3.7 million acres

Volume Protection: 25% of 2015 capacity contains

minimum volume commitments

Investment Opportunities:

Expansion of rich-gas gathering systems

Development of additional processing & fractionation

infrastructure (4 facilities currently under construction)

Development of additional NGL transportation logistics

MarkWest’s Premier Position Drives Incremental Upside

Growth Opportunities

14

Investment Opportunities in Southwest:

Expansion in Gulf Coast

Development of NGL pipelines and

transportation infrastructure

Opportunity in other basins

Investment Opportunities in Utica & Marcellus:

Expansion of dry-gas gathering systems

Expansion of Ohio condensate facility

Long-haul pipelines, storage, and terminal facilities

Developing “Mont Belvieu” capabilities in the

region

Infrastructure to support ethane cracker

development

Investment Opportunities in Northeast:

Development of additional midstream

infrastructure to support the emerging Rogersville

Shale

Significant Synergistic Opportunities

NGL & Condensate Supply

from Marcellus / Utica  Producers

Gas Processing

(Marcellus and

Utica)

Gas

Gathering

Condensate

Fractionation

(Houston and

Hopedale)

Alkylation and

Gasoline Blending

East Coast /

New York Harbor

Midwest Refineries

Stabilizer

(Ohio Condensate)

Cornerstone

Pipeline

Long

Haul

Pipeline

PDH / BDH Facility

Condensate

Splitters (Canton &

Catlettsburg)

Cornerstone and

Other Pipelines

Potential Partnership

Assets

MarkWest Existing

Infrastructure

MPC Existing

Infrastructure

Canadian Diluents

Cornerstone

Midwest Refineries

Other Strategic

Projects

Cornerstone and

Other Pipelines

The combination provides

significant vertical

integration opportunities

between MWE and

MPC/MPLX

Strategic projects:

–

Cornerstone Pipeline

–

Utica condensate

opportunity

–

Alkylation plant

15

Access to Robust Inventory of Drop-downs

$1.6 B of MLP-Eligible EBITDA at MPC

59 MMBbL storage (tanks and caverns)

25 rail loading racks and 24 truck loading racks

7 owned and 11 non-owned docks

2 condensate splitter investments

27 owned and 2,183 leased

794 general service; 1,171 high pressure; 245 open-top hoppers

~ 5,400 miles of additional crude and products pipelines

–

Owns, leases or has an ownership interest in these pipelines

–

0.5% of MPLX Pipe Line Holdings LP

Southern Access Extension, Sandpiper and Utica investments

62 light product; ~20 MMBbL storage; 189 loading lanes

18 asphalt; ~5 MMBbL storage; 65 loading lanes

203 owned and 12 leased inland barges; 5.3 MMBbL capacity

18 owned and one leased inland towboats

20 billion gallons of fuels distribution volume

–

Existing MPC and Speedway volumes; ~17 billion gallons refined products

–

Acquisition of Hess’ retail operations added ~3 billion gallons refined products

16

Railcars

Pipelines

Terminals

Marine

Refineries

Fuels

Distribution

Combination Benefits All Equity Owners

17

Very attractive premium of 32% based on 7/10/15 closing price of MPLX units; 30% based on

MWE’s

30-day

VWAP

Combined entity will have peer leading distribution growth

–

Cash consideration contributed by MPC largely offsets MWE’s medium-term distribution

dilution

Strong sponsor enhances access to capital to fund growth projects

–

Fortune 25 company with $35 B enterprise value

–

Investment grade rating and strong free cash flow generation

–

Lower cost of capital has potential to enhance value

–

Provides liquidity and supports MWE's $1.5 B annual capital plan

–

Enhances ability to pursue new commercial opportunities

–

Potential funding source and "incubator" for capital projects

Adds new growth platform and increases scale and diversity

Industry-leading position

in the Marcellus / Utica, which is in MPC / MPLX's “backyard“

Diversifies customer base and enhances relationships with producers

MWE brings long-term organic growth profile

Complements

Utica

investments

–

Cornerstone

Pipeline

and

build-out

projects

Enhances trading liquidity of MPLX units

Supports strategy to grow higher-valued, stable cash flow midstream business

Opportunity to capture value through numerous incremental growth projects

Expands cash flow profile of general partner

MWE

MPLX

MPC

Note:

1

Volume-weighted average price

17

1

Q&A

18

Appendix

19

Combines a leading natural gas gatherer, processor, and NGL fractionator with a rapidly-growing

downstream / logistics company in the crude oil and refined product business

MPLX will have marquee position in the Marcellus / Utica

"First mover" advantage in other emerging shales

Significant opportunities exist on a combined basis to create value

Significant

Operational

Diversification

Coupled with

Regional Overlap

Strategic Highlights

> 90% of net operating margin is generated by long-term, fee-based contracts

Future organic growth, along with drop-downs, should continue to increase fee-based composition

Target

distribution

coverage

of

1.05x

–

1.10x

MPLX will be managed to support an investment grade credit profile

–

Businesses are primarily fee-based

–

Target leverage of ~4x Debt / Adjusted EBITDA

Investment grade sponsor with significant access to low cost of funding

Combines two attractive platforms with multiple avenues of distributable cash flow growth

Extensive organic growth project profile

Affirm 2015 anticipated distribution growth

guidance of 29%

Combined

partnership

expects

compound

annual

growth

rate

in

distributions

of

25%

through

2017

and approximately 20% annual distribution growth in years 2018 and 2019

$1.6 B inventory of eligible drop-down EBITDA at MPC

Robust Growth

Profile

Creates 4

largest MLP based on market capitalization

Significant operational scale with 6.8 Bcf/d of processing capacity, 379 MBbl/d fractionation capacity,

and ~7,600

miles of pipeline

Increased Size

and Scale

Strong Credit

Profile

Stable Cash Flow

20

th

Proven Track Record of Delivering Results

56% distribution growth since IPO (22% CAGR)

Increased Adjusted EBITDA to $231 MM since IPO

3

Executed three drops totaling $1.2 B in consideration

MPC underpins fee-based, minimum volume

commitment contracts

MPC continues to be aligned with, and supportive of,

MPLX's growth

264% distribution growth since IPO (11% CAGR)

Adjusted EBITDA has grown ~160% from 2010 -

2014

Invested $11.3 B of aggregate capex from

2010 –

2015 YTD

Distribution Since IPO

2

Distribution Since IPO

1

Notes:

1

CAGR calculation assumes MQD paid in Q1 and Q2 of 2002 and actual distributions paid in Q3 and Q4 of 2002

2

At IPO represents Minimum Quarterly Distribution (MQD) annualized

3 LTM 3/31/15 Adjusted EBITDA

21

0.62

1.24

1.49

1.62

1.89

2.16

2.51

2.56

2.57

2.86

3.22

3.38

3.54

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

0.2625

0.2725

0.2850

0.2975

0.3125

0.3275

0.3425

0.3575

0.3825

0.4100

0.2000

0.2400

0.2800

0.3200

0.3600

0.4000

0.4400

At IPO

1Q13

2Q13

3Q13

4Q13

1Q14

2Q14

3Q14

4Q14

1Q15

Increased Size, Diversity and Stability

2015E Growth

Capex ($MM)

% Net Operating

Margin

Fee-Based

6

MWE

Pro Forma MPLX

LP Equity Value ($B)

Enterprise Value ($B)

4

2015E Adjusted

EBITDA ($MM)

5

Notes:

Numbers may not sum due to rounding

1

MPLX at market as of 07/10/15

2

MWE based on transaction consideration.  See “Overview of the Transaction” for detail

3

Pro forma MPLX at market and MWE based on transaction consideration less $675 MM cash component

4

MPLX and Pro Forma MPLX Enterprise Values exclude GP equity value

5

MPLX 2015E Adjusted EBITDA does not assume future drop downs from MPC.  See appendix for non-GAAP reconciliations

6

Non-GAAP measure calculated as segment revenue less purchased product costs

MPLX

~$6

~$6

~$275

$220

~$16

~$20

$925-$1,025

$1,500-$1,900

MarkWest

~$21

~$26

$1,720-$2,120

Pro Forma MPLX

$1,200-$1,300

100%

88%

>90%

Net Debt ($B)

~$1

~$4

~$5

22

2

1

3

1

2

3

Overview of the Transaction

Transaction Summary

Transaction is a 100% equity for equity exchange from

MPLX's perspective

–

MPLX LP issues common units to MWE unitholders at

a fixed exchange ratio of 1.09x

–

Equates

to

~217

million

new

units

issued

1

MPC contributes $675 MM cash to MPLX to pay additional

transaction consideration of $3.37

cash/unit

1

to MWE

unitholders

–

MPC will also contribute an additional $298 million of

cash to MPLX LP to maintain its 2% GP interest

MPLX LP expects to assume all cash and debt outstanding

at MWE

–

$4.2 B of debt and ~$152 MM of cash

No incremental debt will be issued by MPLX or MPC as

a result of the merger

MPLX intends to maintain a leverage ratio of ~4.0x  Debt /

Adjusted EBITDA going forward

Both MPC and MPLX remain committed to preserving

conservative leverage and investment grade credit ratings

Implied MWE Valuation

Sources

and

Uses

Notes:

1

Estimated, based on approximately 200.1 MM fully-diluted MWE common units outstanding, which includes  approximately 8.0 MM MWE Class B units outstanding at close

2

On a fully-diluted basis

Sources ($ MM)

MPLX Equity Issued to MWE

$15,061

MPLX Debt Capacity

4,220

MPC Cash Contribution

675

Total Sources

$19,956

Uses ($ MM)

MWE Equity Acquired

$15,061

MWE Debt Rolled to MPLX

4,220

Cash Consideration to MWE

675

Total Uses

$19,956

23

Equity Consideration:

Exchange Ratio

1.09x

MPLX LP Unit Price (as of 7/10/15)

$69.05

Equity Consideration / Unit

$75.26

MWE

Units

Outstanding

2

200.1

Total Equity Consideration

$15,061

Cash Contribution:

Cash Contribution by MPC

$675

MWE

Units

Outstanding

2

200.1

Cash Contribution / Unit

$3.37

Total Implied Consideration:

Consideration / Unit

$78.64

Implied MWE Equity Value

$15,736

2

Adjusted EBITDA Reconciliations from Net Income

24

Pro Forma

MPLX

MWE

MPLX

($MM)

2015E

2015E

2015E

Net income

200

$               

147

$                

347

$                

Less:  Net income attributable to MPC-retained interest

1

-

1

Net income attributable to MPLX LP

199

$               

147

$                

346

$                

Plus: Net income attributable to MPC-retained interest

1

-

1

Depreciation

54

582

636

Provision for income taxes

1

(11)

(10)

Non-cash equity-based compensation

1

10

11

Net interest and other financial costs

20

214

234

Unrealized loss (gain) on derivative instruments

-

15

15

Adjustment for cash flow from unconsolidated affiliates

-

31

31

Impairment expense

-

26

26

Adjustment for non-controlling interest of consolidated subsidiaries

-

(45)

(45)

Other

-

6

6

Adjusted EBITDA

276

$               

975

$                

1,251

$             

Less:  Adjusted EBITDA attributable to MPC-retained interest

1

-

1

Adjusted EBITDA attributable to MPLX LP

275

$               

975

$                

1,250

$