Document:

Exhibit 10.1

UNIT PURCHASE
AGREEMENT

by and among

MARKWEST ENERGY
PARTNERS, L.P.,

MARKWEST ENERGY
GP, L.L.C.

AND

THE PURCHASERS
PARTY HERETO

UNIT PURCHASE AGREEMENT

UNIT PURCHASE AGREEMENT, dated as of April 9, 2007
(this “Agreement”), by and among MARKWEST ENERGY PARTNERS, L.P. (“MarkWest”),
MARKWEST ENERGY GP, L.L.C. (“MarkWest GP”) (solely for purposes of
Section 6.12) and each of the purchasers set forth on Schedule 2.02
hereof (each a “Purchaser” and collectively, the “Purchasers”).

In consideration of the mutual covenants and
agreements set forth herein and for good and valuable consideration, the
receipt of which is hereby acknowledged, the parties hereby agree as follows:

ARTICLE I

DEFINITIONS

Section 1.01           Definitions.  As used in this Agreement, and unless the
context requires a different meaning, the following terms have the meanings
indicated:

“Action” against a Person means any lawsuit,
action, proceeding, investigation or complaint before any Governmental
Authority, mediator or arbitrator.

“Affiliate” means, with respect to a specified
Person, any other Person, directly or indirectly controlling, controlled by or
under direct or indirect common control with such specified Person.  For purposes of this definition, “control”
(including, with correlative meanings, “controlling,” “controlled by,” and “under
common control with”) means the power to direct or cause the direction of the
management and policies of such Person, directly or indirectly, whether through
the ownership of voting securities, by contract or otherwise.

“Agreement” has the meaning set forth in the
introductory paragraph.

“Basic Documents” means, collectively, this
Agreement, the Registration Rights Agreement, and any and all other agreements
or instruments executed and delivered to the Purchasers by MarkWest or any
Subsidiary of MarkWest hereunder or thereunder.

“Business Day” means any day other than a
Saturday, Sunday, or a legal holiday for commercial banks in New York, New
York.

“Closing” shall have the meaning specified in
Section 2.02.

“Closing Date” shall have the meaning specified
in Section 2.02.

“Commission” means the United States Securities
and Exchange Commission.

“Common Units” means the common units of
MarkWest.

“Confidential Information” means all oral or
written information, documents, records and data that MarkWest or its
Representatives furnishes or otherwise discloses to a Purchaser or any of its
Representatives, together with all copies, extracts, analyses, compilations,
studies, memoranda, notes or other documents, records or data (in whatever form
maintained, whether 

documentary, computer or other electronic storage or
otherwise) prepared by any Person that contain or otherwise reflect or are
generated from such information, documents, records, or data.  The term “Confidential Information” does not
include any information that (a) at the time of disclosure or thereafter is
generally available to the public (other than as a result of a disclosure by
such Purchaser or its Representatives), (b) is developed by such Purchaser or
any of its Representatives, independent of, and without reliance in whole or in
part on, any Confidential Information or any knowledge of Confidential
Information, (c) becomes available to such Purchaser or its Representatives on
a non-confidential basis from a source other than MarkWest or its
Representatives who, insofar as is known to the recipient after reasonable
inquiry, is not prohibited from transmitting the information to the recipient
by a contractual, legal, fiduciary or other obligation to MarkWest or (d) was
available to such Purchaser or its Representatives on a non-confidential basis
prior to its disclosure to such Purchaser or its Representatives by MarkWest or
its Representatives.

“Exchange Act” means the Securities Exchange
Act of 1934, as amended from time to time, and the rules and regulations of the
Commission promulgated thereunder.

“Form 8-A” shall have the meaning set forth in
Section 3.02(a).

“GAAP” means generally accepted accounting
principles in the United States of America in effect from time to time.

“Governmental Authority” means, with respect to
a particular Person, the country, state, county, city and political
subdivisions in which such Person or such Person’s Property is located or which
exercises valid jurisdiction over any such Person or such Person’s Property,
and any court, agency, department, commission, board, bureau or instrumentality
of any of them and any monetary authority which exercises valid jurisdiction
over any such Person or such Person’s Property. 
Unless otherwise specified, all references to Governmental Authority
herein with respect to MarkWest means a Governmental Authority having jurisdiction
over MarkWest, its Subsidiaries or any of their respective Properties.

“Hydrocarbon Transaction” shall have the
meaning specified in Section 4.03.

“Indemnified Party” shall have the meaning
specified in Section 6.02(c).

“Indemnifying Party” shall have the meaning
specified in Section 6.02(c).

“Knowledge” means the actual knowledge of the
individuals listed on Schedule 1.01 hereto after reasonable
inquiry.

“Law” means any federal, state, local or
foreign order, writ, injunction, judgment, settlement, award, decree, statute,
law, rule or regulation.

“Lien” means any lien, encumbrance, security
interest, charge or other interest in Property securing an obligation owed to,
or a claim by, a Person other than the owner of the Property, whether such interest
is based on the common law, statute or contract, and whether such obligation or
claim is fixed or contingent, and including but not limited to the lien or
security interest arising from a mortgage, encumbrance, pledge, security
agreement, conditional 

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sale or trust receipt or
a lease, consignment or bailment for security purposes. For the purpose of this
Agreement, a Person shall be deemed to be the owner of any Property which it
has acquired or holds subject to a conditional sale agreement, or leases under
a financing lease or other arrangement pursuant to which title to the Property
has been retained by or vested in some other Person in a transaction intended
to create a financing.

“MarkWest” has the meaning set forth in the
introductory paragraph.

“MarkWest Financial Statements” means the
financial statement or statements described or referred to in Section 3.03.

“MarkWest GP” has the meaning set forth in the
introductory paragraph.

“MarkWest Material Adverse Effect” means any
material and adverse effect on (a) the assets, liabilities, financial
condition, business, operations or affairs of MarkWest and its Subsidiaries
taken as a whole measured against those assets, liabilities, financial
condition, business, operations or affairs reflected in the MarkWest SEC
Documents filed with the Commission prior to the date hereof or from the facts
represented or warranted in any Basic Document, or (b) the ability of MarkWest
to fulfill any of its obligations under or consummate any of the transactions
contemplated by the Basic Documents.

“MarkWest Related Parties” shall have the
meaning specified in Section 6.02(b).

“MarkWest SEC Documents” shall have the meaning
specified in Section 3.03.

“Partnership Agreement” means the Second
Amended and Restated Agreement of Limited Partnership of MarkWest, dated as of
February 28, 2007.

“Partnership Securities” means any class or
series of equity interest in MarkWest (but excluding any options, rights,
warrants and appreciation rights relating to an equity interest in MarkWest),
including without limitation Common Units, Subordinated Units and Incentive
Distribution Rights (as defined in the Partnership Agreement).

“Permits” means, with respect to MarkWest or
any of its Subsidiaries, any licenses, permits, variances, consents,
authorizations, waivers, grants, franchises, concessions, exemptions, orders,
registrations and approvals of Governmental Authorities or other Persons
necessary for the ownership, leasing, operation, occupancy and use of its
Properties and the conduct of its businesses as currently conducted.

“Person” means any individual, corporation,
company, voluntary association, partnership, joint venture, trust, limited
liability company, unincorporated organization or government or any agency,
instrumentality or political subdivision thereof, or any other form of entity.

“Property” means any interest in any kind of
property or asset, whether real, personal or mixed, or tangible or intangible.

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“Purchase Price” means, with respect to a
particular Purchaser, the monetary purchase amount set forth opposite such
Purchaser’s name under the column entitled “Total Purchase Price” on Schedule
2.02 hereto.

“Purchased Units” means, with respect to a
particular Purchaser, the number of Common Units set forth opposite such Purchaser’s
name under the column entitled “Units Purchased” set forth on Schedule 2.02
hereto.

“Purchaser” and “Purchasers” each has
the meaning set forth in the introductory paragraph.

“Purchaser Material Adverse Effect” means, with
respect to a particular Purchaser, any material and adverse effect on (a) the
assets, liabilities, financial condition, business, operations or affairs of
such Purchaser, (b) the ability of such Purchaser to carry out its business as
of the date hereof or to meet its obligations under the Basic Documents on a
timely basis or (c) the ability of such Purchaser to consummate the
transactions under any Basic Document.

“Purchaser Related Parties” shall have the
meaning specified in Section 6.02(a).

“Registration Rights Agreement” means the
Registration Rights Agreement, to be entered into at the Closing, among
MarkWest and the Purchasers in the form attached hereto as Exhibit A.

“Representatives” of any Person means the
officers, directors, employees, agents, counsel, investment bankers and other
representatives of such Person.

“Securities Act” means the Securities Act of
1933, as amended from time to time, and the rules and regulations of the
Commission promulgated thereunder.

“Subordinated Units” means the subordinated
units of MarkWest.

“Subsidiary” means, as to any Person, any
corporation or other entity of which: (i) such Person or a Subsidiary of such
Person is a general partner or manager; or (ii) at least a majority of the
outstanding equity interest having by the terms thereof ordinary voting power
to elect a majority of the board of directors or similar governing body of such
corporation or other entity (irrespective of whether or not at the time any
equity interest of any other class or classes of such corporation or other entity
shall have or might have voting power by reason of the happening of any
contingency) is at the time directly or indirectly owned or controlled by such
Person or one or more of its Subsidiaries.

“Tax” means any tax, charge, fee, levy, penalty
or other assessment imposed by any U.S. federal, state, local or foreign taxing
authority, including any excise, property, income, sales, transfer, franchise,
payroll, withholding, social security or other tax, including any interest,
penalties or additions attributable thereto.

“Tax Return” means any return, report,
information return, declaration, claim for refund or other document (including
any related or supporting information) supplied or required to be 

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supplied to any authority
with respect to Taxes and including any supplement or amendment thereof.

“Unit Price” shall have the
meaning set forth in Section 2.04.

Section 1.02           Accounting Procedures and
Interpretation.  Unless otherwise
specified herein, all accounting terms used herein shall be interpreted, all determinations
with respect to accounting matters hereunder shall be made, and all MarkWest
Financial Statements and certificates and reports as to financial matters
required to be furnished to the Purchasers hereunder shall be prepared, in
accordance with GAAP applied on a consistent basis during the periods involved
(except, in the case of unaudited statements, as permitted by Form 10-Q
promulgated by the Commission) and in compliance as to form in all material
respects with applicable accounting requirements and with the published rules
and regulations of the Commission with respect thereto.

ARTICLE II

AGREEMENT TO SELL AND PURCHASE

Section 2.01           Sale and Purchase.  Subject to the terms and conditions hereof,
at the Closing (as defined in Section 2.02) MarkWest hereby agrees to issue and
sell to each Purchaser, and each Purchaser hereby agrees to purchase from
MarkWest, such Purchaser’s Purchased Units, and each Purchaser agrees to pay
MarkWest such Purchaser’s Purchase Price. The obligation of each Purchaser
hereunder is several and not joint and is independent of the obligation of each
other Purchaser, and the failure of, or MarkWest’s waiver of, performance by
any Purchaser does not excuse performance by any other Purchaser or MarkWest.

Section 2.02           Closing.  Subject to the terms and conditions hereof,
the consummation of the purchase and sale of the Purchased Units hereunder (the
“Closing”) shall take place on April 9, 2007 (such date, the “Closing
Date”) at the offices of Vinson & Elkins, L.L.P., 1001 Fannin Street,
Suite 2500, Houston, Texas 77002.  Each
of the items to be delivered, as set forth in Section 2.03, shall be delivered
by the responsible party on the Closing Date.

Section 2.03           Deliveries.

(a)           At the Closing, subject to the terms
and conditions hereof, MarkWest will deliver, or cause to be delivered, to each
Purchaser:

(i)                    The Purchased Units to be
purchased by such Purchaser by delivery of certificates evidencing such
Purchased Units at the Closing meeting the requirements of the Partnership Agreement,
all free and clear of any Liens, encumbrances or interests of any other Person;

(ii)                   A certificate of the
Secretary of State of the State of Delaware, dated as of a recent date, that
each of MarkWest, MarkWest GP and MarkWest Energy Operating Company, L.L.C. is
in good standing;

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(iii)                  An opinion addressed to the
Purchasers from Vinson & Elkins L.L.P., dated as of the Closing Date, in
the form and substance attached hereto as Exhibit C;

(iv)                  The Registration Rights
Agreement, which shall have been duly executed by MarkWest.

(b)           At the Closing, subject to the terms
and conditions hereof, each Purchaser will deliver, or cause to be delivered to
MarkWest.

(i)                    The Registration Rights
Agreement, which shall have been duly executed by each such Purchaser; and

(ii)                   Such Purchaser’s Purchase
Price by wire transfer of immediately available funds to an account designated
by MarkWest in writing prior to the Closing.

Section 2.04           Consideration.  The amount per Common Units each Purchaser
will pay to MarkWest to purchase the Common Units comprising the Purchased
Units shall be $32.98 per Common Unit. (the
“Unit Price”).

Section
2.05           Independent Nature of
Purchasers’ Obligations and Rights.  The obligations of each Purchaser under
any Basic Document are several and not joint with the obligations of any other
Purchaser, and no Purchaser shall be responsible in any way for the performance
of the obligations of any other Purchaser under any Basic Document.  Nothing contained herein or in any Basic
Document, and no action taken by any Purchaser pursuant thereto, shall be
deemed to constitute the Purchasers as a partnership, an association, a joint
venture or any other kind of entity, or create a presumption that the
Purchasers are in any way acting in concert or as a group with respect to such
obligations or the transactions contemplated by the Basic Document.  Each Purchaser shall be entitled to
independently protect and enforce its rights, including without limitation, the
rights arising out of this Agreement or out of the other Basic Documents, and
it shall not be necessary for any other Purchaser to be joined as an additional
party in any proceeding for such purpose. 
Each Purchaser has been represented by its own separate legal counsel in
their review and negotiation of the Basic Documents.   MarkWest has elected to provide all
Purchasers with the same material terms and Basic Documents for the convenience
of MarkWest and not because it was required or requested to do so by the
Purchasers.

Section 2.06           Lock-up.

(a)           MarkWest agrees that from and after
Closing it will not sell, nor will it permit any of its Affiliates to offer,
sell, contract to sell, pledge, or otherwise dispose of, or enter into any
transaction which is designed to, or might reasonably be expected to, result in
the disposition of any Common Units prior to the date which is 90 days from the
Closing Date.

(b)           Each Purchaser agrees that from and
after Closing it will not offer, sell, contract to sell, pledge, or otherwise
dispose of, or enter into any transaction which is 

 6
 

designed to, or might
reasonably be expected to, result in the disposition of any of the Purchased
Units prior to the date which is 90 days from the Closing Date; provided,
however, that any Purchaser may enter into a cash settled derivative, total
return swap or similar transaction with respect to the Purchased Units
purchased by it.

ARTICLE III

REPRESENTATIONS AND WARRANTIES RELATED TO
MARKWEST

MarkWest represents and warrants to each Purchaser as
follows:

Section 3.01           Corporate Existence.  MarkWest: (a) is a limited partnership duly
organized, legally existing and in good standing under the laws of the State of
Delaware; and (b) has all requisite power and authority, and has all
governmental licenses, authorizations, consents and approvals necessary, to
own, lease, use and operate its Properties and carry on its business as its
business is now being conducted, except where the failure to obtain such
licenses, authorizations, consents and approvals would not be reasonably likely
to have a MarkWest Material Adverse Effect. 
Each of MarkWest’s Subsidiaries that is a corporation is a corporation
duly incorporated, validly existing and in good standing under the laws of the
State or other jurisdiction of its incorporation and has all requisite power
and authority, and has all governmental licenses, authorizations, consents and
approvals necessary, to own, lease, use or operate its respective Properties
and carry on its business as now being conducted, except where the failure to
obtain such licenses, authorizations, consents and approvals would not be
reasonably likely to have a MarkWest Material Adverse Effect.  Each Subsidiary of MarkWest that is not a
corporation has been duly formed, is validly existing and in good standing
under the laws of the State or other jurisdiction of its formation and has all
requisite power and authority, and has all governmental licenses,
authorizations, consents and approvals necessary, to own, lease, use or operate
its respective Properties and carry on its business as now being conducted,
except where the failure to obtain such licenses, authorizations, consents and
approvals would not be reasonably likely to have a MarkWest Material Adverse
Effect.  None of MarkWest or any of its
Subsidiaries are in default in the performance, observance or fulfillment of
any provision of, in the case of MarkWest, the Partnership Agreement or its
Certificate of Limited Partnership or, in the case of any Subsidiary of
MarkWest, its respective certificate of incorporation, bylaws or other similar
organizational documents.  Each of
MarkWest and its Subsidiaries is duly qualified or licensed and in good
standing as a foreign corporation or other entity, and is authorized to do
business, in each jurisdiction in which the ownership or leasing of its
respective Properties or the character of its respective operations makes such
qualification necessary, except where the failure to obtain such qualification,
license, authorization or good standing would not be reasonably likely to have
a MarkWest Material Adverse Effect.

Section 3.02           Capitalization and Valid Issuance
of Purchased Units.

(a)           As of the date hereof, the issued and
outstanding limited partner interests of MarkWest consist of 31,206,514 Common
Units and 1,200,000 Subordinated Units. 
The only issued and outstanding general partner interests of MarkWest
are the interests of the General Partner described and as defined in the
Partnership Agreement.  All 

 7
 

outstanding Common Units
and Subordinated Units and the limited partner interests represented thereby
have been duly authorized and validly issued in accordance with the Partnership
Agreement and are fully paid (to the extent required under the Partnership
Agreement) and nonassessable (except as such nonassessability may be affected by
matters described under the caption “The Partnership Agreement-Limited
Liability” in MarkWest’s registration statement on Form S-1 (No. 333-81780)
which is incorporated by reference into the Partnership’s Registration
Statement on Form 8-A (File No. 001-31239) (the “Form 8-A”)).

(b)           Other than MarkWest’s Long-Term
Incentive Plan and MarkWest’s other equity compensation plans, as described in
MarkWest’s Annual Report on Form 10-K for the period ended December 31, 2006,
MarkWest has no equity compensation plans that contemplate the issuance of
Common Units (or securities convertible into or exchangeable for Common
Units).  No indebtedness having the right
to vote (or convertible into or exchangeable for securities having the right to
vote) on any matters on which MarkWest unitholders may vote is issued or
outstanding.  Except as set forth in the
first sentence of this Section 3.02(b) or as are contained in the Partnership
Agreement, there are no outstanding or authorized (i) options, warrants,
preemptive rights, subscriptions, calls, or other rights, convertible
securities, agreements, claims or commitments of any character obligating
MarkWest or any of its Subsidiaries to issue, transfer or sell any partnership
interests or other equity interest in, MarkWest or any of its Subsidiaries or
securities convertible into or exchangeable for such partnership interests or
equity interests, (ii) obligations of MarkWest or any of its Subsidiaries to
repurchase, redeem or otherwise acquire any partnership interests or equity
interests of MarkWest or any of its Subsidiaries or any such securities or
agreements listed in clause (i) of this sentence or (iii) voting trusts or
similar agreements to which MarkWest or any of its Subsidiaries is a party with
respect to the voting of the equity interests of MarkWest or any of its
Subsidiaries.  At the Closing, except as
described in this Section 3.02(b), there will not be any outstanding
subscriptions, options, warrants, calls, preemptive rights, subscriptions, or
other rights, convertible or exchangeable securities, agreements, claims or
commitments of any character by which MarkWest or any of its Subsidiaries will
be bound calling for the purchase or issuance of any partnership interests of
MarkWest or any equity interest of any of its Subsidiaries or securities
convertible into or exchangeable for such partnership or equity interests or
any other such securities or agreements. 
Neither the offering or sale of the Purchased Units nor registration of
the Purchased Units pursuant to the Registration Rights Agreement gives rise to
any rights for or relating to the registration of any Common Units or other
securities of MarkWest.

(c)           (i) All of the issued and outstanding
equity interests of each of MarkWest’s Subsidiaries are owned, directly or
indirectly, by MarkWest free and clear of any Liens (except for such
restrictions as may exist under applicable Law and except for such Liens as may
be imposed under MarkWest’s or MarkWest’s Subsidiaries’ credit facilities), and
all such ownership interests have been duly authorized, validly issued and are
fully paid (to the extent required in the organizational documents of MarkWest’s
Subsidiaries, as applicable) and non-assessable (except as nonassessability may
be affected by Section 6.07 of the Texas Revised Uniform Limited Partnership
Act,  Section 18-607 of the Delaware
Limited Liability Company Act, Section 17-607 of the 

 8
 

Delaware Revised Uniform
Limited Partnership Act, Section 450.4307 of the Michigan Limited Liability
Company Act, Section 2030 of the Oklahoma Limited Liability Company Act or the
organizational documents of MarkWest’s Subsidiaries, as applicable) and free of
preemptive rights, with no personal liability attaching to the ownership
thereof, and (ii) as of the date hereof, neither MarkWest nor any of its
Subsidiaries owns any shares of capital stock or other securities of, or
interest in, any other Person, or is obligated to make any capital contribution
to or other investment in any other Person. 
The material Subsidiaries of MarkWest are set forth on Schedule 3.02
hereto.

(d)           The Common Units being purchased by
the Purchasers hereunder and the limited partner interests represented thereby,
are duly authorized by the Partnership Agreement and, when issued and delivered
to the Purchasers against payment therefor in accordance with the terms of this
Agreement, will be validly issued, fully paid (to the extent required by the
Partnership Agreement) and nonassessable (except as such nonassessability may
be affected by matters described under the caption “The Partnership
Agreement—Limited Liability” in MarkWest’s registration statement on Form S-1
(No. 333-81780) which is incorporated by reference into the Form 8-A) and will
be free of any and all Liens and restrictions on transfer, other than
restrictions on transfer under the Partnership Agreement and under applicable
state and federal securities laws and other than such Liens as are created by
the Purchaser.

(e)           The Common Units are listed on the
American Stock Exchange.

(f)            Correct and complete copies of the
Partnership Agreement and MarkWest’s certificate of limited partnership are
attached hereto as Exhibit B.

Section 3.03           MarkWest SEC Documents.  MarkWest has filed with the Commission all
forms, registration statements, reports, schedules and statements required to
be filed by it under the Exchange Act or the Securities Act (all such
documents, collectively “MarkWest SEC Documents”) and since
October 11, 2005, all such reports and statements have been timely
filed.  The MarkWest SEC Documents,
including, without limitation, any audited or unaudited financial statements
and any notes thereto or schedules included therein (the “MarkWest Financial
Statements”), at the time filed (in the case of registration statements,
solely on the dates of effectiveness) (except to the extent corrected by a
subsequently filed MarkWest SEC Document filed prior to the date hereof) (a)
did not contain any untrue statement of a material fact or omit to state a
material fact required to be stated therein or necessary in order to make the
statements therein, in light of the circumstances under which they were made,
not misleading, (b) complied in all material respects with the applicable
requirements of the Exchange Act and the Securities Act, as the case may be,
(c) complied as to form in all material respects with applicable accounting
requirements and with the published rules and regulations of the Commission
with respect thereto, (d) were prepared in accordance with GAAP applied on a
consistent basis during the periods involved (except as may be indicated in the
notes thereto or, in the case of unaudited statements, as permitted by Form
10-Q of the Commission), and (e) fairly present (subject in the case of
unaudited statements to normal, recurring and year-end audit adjustments) in
all material respects the consolidated financial position and status of the
business of MarkWest as of the dates thereof and the consolidated results of
its operations and cash flows 

 9
 

for the periods then ended.  PricewaterhouseCoopers LLP, MarkWest’s former
public accounting firm, is an independent public accounting firm with respect
to MarkWest and did not resign and was not dismissed as independent public
accountants of MarkWest as a result of or in connection with any disagreement
with MarkWest on a matter of accounting principles or practices, financial
statement disclosure or auditing scope or procedure.  KPMG LLP, MarkWest’s former public accounting
firm, is an independent public accounting firm with respect to MarkWest and did
not resign and was not dismissed as independent public accountants of MarkWest
as a result of or in connection with any disagreement with MarkWest on a matter
of accounting principles or practices, financial statement disclosure or
auditing scope or procedure.  Deloitte
& Touche LLP, MarkWest’s current public accounting firm, is an independent
public accounting firm with respect to MarkWest and has not resigned or been
dismissed as independent public accountants of MarkWest as a result of or in
connection with any disagreement with MarkWest on a matter of accounting
principles or practices, financial statement disclosure or auditing scope or
procedure.  To MarkWest’s Knowledge, the
information (considering all information in the aggregate and excluding all
forecasts, projections and forward looking information), if any, provided by
MarkWest to any Purchaser regarding any potential transaction with MarkWest
Hydrocarbon, Inc. was true and correct in all material respects and did not
contain any untrue statement of a material fact or omit to state a material
fact required to be stated therein or necessary in order to make the statements
therein, in light of the circumstances under which they were made, not
misleading.

Section 3.04           No Material Adverse Change.  Except as set forth in or contemplated by the
MarkWest SEC Documents filed with the Commission on or prior to the date hereof
and all matters related to any potential transaction with MarkWest Hydrocarbon,
Inc. which have been discussed with each of the Purchasers, since December 31,
2006, MarkWest and its Subsidiaries have conducted their respective businesses
in the ordinary course, consistent with past practice, and there has been no
(a) change, event, occurrence, effect, fact, circumstance or condition that has
had or would be reasonably likely to have a MarkWest Material Adverse Effect,
other than those occurring as a result of general economic or financial
conditions or other developments that are not unique to MarkWest and its
Subsidiaries but also affect other Persons who participate or are engaged in
the lines of business of which MarkWest and its Subsidiaries participate or are
engaged, except, in each case, to the extent such change, event, occurrence,
effect, fact, circumstance or condition affects MarkWest to a significantly
greater extent than other similarly situated companies generally, (b)
acquisition or disposition of any material asset by MarkWest or any of its
Subsidiaries or any contract or arrangement therefor, otherwise than for fair
value in the ordinary course of business, or (c) material change in MarkWest’s
accounting principles, practices or methods. 
Except as set forth in or contemplated by the MarkWest SEC Documents
filed with the Commission on or prior to the date hereof and MarkWest has
neither issued Partnership Securities (other than under its Long-Term Incentive
Plan and its other equity compensation plans, each as described in the MarkWest
SEC Documents filed with the Commission on or prior to the date hereof) nor
incurred material indebtedness since December 31, 2006.

Section 3.05           Litigation.  Except as set forth in the MarkWest SEC
Documents filed with the Commission on or prior to the date hereof, there is no
Action pending or, to the knowledge of MarkWest, contemplated or threatened
against or affecting MarkWest, any of its Subsidiaries or any of their
respective officers, directors, properties or assets, which (individually 

 10
 

or in the aggregate) (a) questions the validity of any
of the Basic Documents or the right of MarkWest to enter into any of the Basic
Documents or to consummate the transactions contemplated hereby and thereby or
(b) would be reasonably likely to result in a MarkWest Material Adverse Effect.

Section 3.06           No Breach.  The execution, delivery and performance by
MarkWest of the Basic Documents and all other agreements and instruments to be
executed and delivered by MarkWest pursuant hereto or thereto or in connection
with the transactions contemplated by the Basic Documents or any such other
agreements and instruments, and compliance by MarkWest with the terms and
provisions hereof and thereof and the issuance and sale by MarkWest of the
Purchased Units, do not and will not (a) violate any provision of any Law or
Permit having applicability to MarkWest or any of its Subsidiaries or any of
their respective Properties, (b) conflict with or result in a violation of any
provision of the Certificate of Limited Partnership or other organizational
documents of MarkWest, or the Partnership Agreement, or any organizational
documents of any of MarkWest’s Subsidiaries, (c) require any consent, approval
or notice under or result in a violation or breach of or constitute (with or
without due notice or lapse of time or both) a default (or give rise to any
right of termination, cancellation or acceleration) under any contract,
agreement, instrument, obligation, note, bond, mortgage, license, loan or
credit agreement to which MarkWest or any of its Subsidiaries is a party or by
which MarkWest or any of its Subsidiaries or any of their respective Properties
may be bound, or (d) result in or require the creation or imposition of any
Lien upon or with respect to any of the Properties now owned or hereafter
acquired by MarkWest or any of its Subsidiaries; with the exception of the
conflicts stated in clause (b) of this Section 3.06, except where such
conflict, violation, default, breach, termination, cancellation, failure to
receive consent or approval, or acceleration with respect to the foregoing
provisions of this Section 3.06 would not be, individually or in the aggregate,
reasonably likely to have a MarkWest Material Adverse Effect.

Section 3.07           Authority.  MarkWest has all necessary power and
authority to execute, deliver and perform its obligations under the Basic
Documents and the execution, delivery and performance by MarkWest of the Basic
Documents; and the Basic Documents constitute the legal, valid and binding
obligations of MarkWest, enforceable in accordance with their terms, except as
such enforceability may be limited by bankruptcy, insolvency, fraudulent
transfer and similar laws affecting creditors’ rights generally or by general
principles of equity. No approval from the holders of the Common Units is
required in connection with MarkWest’s issuance and sale of the Purchased Units
to the Purchasers.

Section 3.08           Approvals.  Except for the approvals required by the
Commission in connection with MarkWest’s obligations under the Registration
Rights Agreement, no authorization, consent, approval, waiver, license, qualification
or written exemption from, nor any filing, declaration, qualification or
registration with, any Governmental Authority or any other Person is required
in connection with the execution, delivery or performance by MarkWest of any of
the Basic Documents, except those already obtained or where the failure to
receive such authorization, consent, approval, waiver, license, qualification
or written exemption from, or to make such filing, declaration, qualification
or registration would not, individually or in the aggregate, be reasonably
likely to have a MarkWest Material Adverse Effect.

 11
 

Section 3.09           MLP Status.  MarkWest has, for each taxable year beginning
after December 31, 2002, during which MarkWest was in existence, met the gross
income requirements of Section 7704(c)(2) of the Internal Revenue Code of 1986,
as amended.

Section 3.10           Offering.  Assuming the accuracy of the representations
and warranties of the Purchasers contained in this Agreement, the sale and
issuance of the Purchased Units to each of the Purchasers pursuant to this
Agreement is exempt from the registration requirements of the Securities Act,
and neither MarkWest nor any authorized agent acting on its behalf has taken or
will take any action hereafter that would cause the loss of such exemptions.

Section 3.11           Investment Company Status.  MarkWest is not an “investment company”
within the meaning of the Investment Company Act of 1940, as amended.

Section 3.12           Certain Fees.  Except for the expense reimbursement
contemplated by Section 6.11, no fees or commissions will be payable by
MarkWest to brokers, finders, or investment bankers with respect to the sale of
any of the Purchased Units or the consummation of the transaction contemplated
by this Agreement.  

Section 3.13           No Side Agreements.  There are no other agreements by, among or
between MarkWest or its Affiliates, on the one hand, and any of the Purchasers
or their Affiliates, on the other hand, with respect to the transactions
contemplated hereby nor promises or inducements for future transactions between
or among any of such parties.  

Section 3.14           Material Agreements.  MarkWest has provided the Purchasers (if
requested) with correct and complete copies of all material agreements (as
defined in Item 601(b)(10) of Regulation S-K promulgated by the
Commission), including amendments to or other modifications of pre-existing
material agreements, entered into by MarkWest since December 31, 2006.

Section 3.15           Form S-3 Eligibility and WKSI
Status.  MarkWest is eligible to
register the Purchased Units for resale by the Purchasers on a registration
statement on Form S-3 under the Securities Act. MarkWest qualifies as a “well-known
seasoned issuer” under the Exchange Act.

Section 3.16           Taxes.  MarkWest has filed all Tax Returns required
to be filed.  To the knowledge of
MarkWest, such Tax Returns are true, correct and complete in all material
respects.  MarkWest has paid in full all
Taxes shown to be due on such tax returns. 
MarkWest has not received any written notice of deficiency or assessment
from any taxing authority with respect to liabilities for material Taxes, which
have not been fully paid or finally settled, unless being contested in good
faith through appropriate proceedings and for which adequate reserves are
presented on the MarkWest Financial Statements.

Section 3.17           Confidential Information.  MarkWest has not provided any Purchaser
Confidential Information, including Confidential Information regarding the
Hydrocarbon Transaction, except for the existence of the proposed offering of
Purchased Units, unless requested by such Purchaser.

 12

ARTICLE IV

REPRESENTATIONS AND WARRANTIES OF EACH
PURCHASER

Each Purchaser, severally and not jointly, represents
and warrants to MarkWest with respect to itself:

Section 4.01           Investment.  The Purchased Units are being acquired for
its own account, not as a nominee or agent, and with no intention of
distributing the Purchased Units or any part thereof, and that such Purchaser
has no present intention of selling or granting any participation in or
otherwise distributing the same in any transaction in violation of the
securities laws of the United States of America or any State, without
prejudice, however, to such Purchaser’s right at all times to sell or otherwise
dispose of all or any part of the Purchased Units under a registration
statement under the Securities Act and applicable state securities laws or
under an exemption from such registration available thereunder (including,
without limitation, if available, Rule 144 promulgated thereunder). If such
Purchaser should in the future decide to dispose of any of the Purchased Units,
such Purchaser understands and agrees (a) that it may do so only (i) in
compliance with the Securities Act and applicable state securities law, as then
in effect, or (ii) in the manner contemplated by any registration statement pursuant
to which such securities are being offered, and (b) that stop-transfer
instructions to that effect will be in effect with respect to such
securities.  Notwithstanding the
foregoing, a Purchaser may enter into a derivative transaction or one or more total
return swaps with respect to its Purchased Units with a third party provided
that such transaction is exempt from registration under the Securities Act.

Section 4.02           Nature of Purchaser.  Such Purchaser represents and warrants to,
and covenants and agrees with, MarkWest that, (a) it is an “accredited investor”
within the meaning of Rule 501 of Regulation D promulgated by the Commission
pursuant to the Securities Act and (b) by reason of its business and financial
experience it has such knowledge, sophistication and experience in making
similar investments and in business and financial matters generally so as to be
capable of evaluating the merits and risks of the prospective investment in the
Purchased Units, is able to bear the economic risk of such investment and, at
the present time, would be able to afford a complete loss of such investment.

Section 4.03           Receipt of Information;
Authorization.  Such Purchaser
acknowledges that it has (a) had access to MarkWest’s periodic filings
with the Commission, including MarkWest’s Annual Report on Form 10-K, as filed
with the Commission on March 7, 2007, for the year ended December 31,
2006, MarkWest’s Amendment No. 1 to its Annual Report on Form 10-K/A, as filed
with the Commission on March 15, 2007, for the year ended December 31,
2006 and all Current Reports on Form 8-K filed with the Commission by MarkWest
since January 1, 2007, (b) been informed that the Board of Directors of
MarkWest has asked its Conflicts Committee to review and evaluate a possible acquisition
of, business combination with, or other potential restructuring transaction
with MarkWest Hydrocarbon, Inc. (the “Hydrocarbon Transaction”) and
understands the potential risks related to the Hydrocarbon Transaction and the
failure to consummate the Hydrocarbon Transaction, including without
limitation, (i) near or long-term dilution to existing unitholders, (ii)
decrease in distributions paid to unitholders, (iii) negative impact on the
trading price of the Common Units, and (iv) uncertainty as to timing, form and
ultimate consummation of the Hydrocarbon Transaction and (c) been provided a 

 13
 

reasonable opportunity to ask questions of and receive
answers from Representatives of MarkWest regarding such matters.

Section 4.04           Corporate Existence.  Such Purchaser, if an entity: (a) is duly
incorporated or formed, legally existing and in good standing under the laws of
its respective jurisdiction of incorporation or formation; and (b) has all
requisite power and authority, and has all governmental licenses, authorizations,
consents and approvals necessary, to own, lease, use and operate its Properties
and carry on its business as its business is now being conducted, except where
the failure to obtain such licenses, authorizations, consents and approvals
would not be reasonably likely to have a Purchaser Material Adverse Effect.
Each such Purchaser is not in default in the performance, observance or
fulfillment of any provision of its organizational documents, except where such
default would not have or would not be reasonably likely to have a Purchaser
Material Adverse Effect.

Section 4.05           No Breach.  The execution, delivery and performance by
such Purchaser of this Agreement, the Registration Rights Agreement and all
other agreements and instruments to be executed and delivered by such Purchaser
pursuant hereto or thereto or in connection with the transactions contemplated
by this Agreement, the Registration Rights Agreement or any such other
agreements and instruments, and compliance by such Purchaser with the terms and
provisions hereof and thereof, and the purchase of such Purchaser’s Purchased
Units by such Purchaser do not and will not (a) violate any provision of any
Law or permit having applicability to such Purchaser or any of its Properties,
(b) conflict with or result in a violation of any provision of the
organizational documents of such Purchaser, (c) require any consent or approval
under or result in a violation or breach of or constitute (with or without due
notice or lapse of time or both) a default (or give rise to any right of
termination, cancellation or acceleration) under any contract, agreement,
instrument, obligation, note, bond, mortgage, license, loan or credit agreement
to which such Purchaser is a party or by which such Purchaser or any of its
Properties may be bound, or (d) result in or require the creation or imposition
of any Lien upon or with respect to any of the Properties now owned or
hereafter acquired by such Purchaser; with the exception of the conflicts
stated in clause (b) of this Section 4.05, except where such conflict,
violation, default, breach, termination, cancellation, failure to receive
consent or approval, or acceleration with respect to the foregoing provisions
of this Section 4.05 would not, individually or in the aggregate, be reasonably
likely to have a Purchaser Material Adverse Effect.

Section 4.06           Restricted Securities.  Such Purchaser understands that the Purchased
Units it is purchasing are characterized as “restricted securities” under the
federal securities laws inasmuch as they are being acquired from MarkWest in a
transaction not involving a public offering and that under such laws and
applicable regulations such securities may be resold without registration under
the Securities Act only in certain limited circumstances. In this connection,
Purchaser represents that it is knowledgeable with respect to Rule 144 of the
Commission promulgated under the Securities Act.

Section 4.07           Certain Fees.  No fees or commissions will be payable by
such Purchaser to brokers, finders, or investment bankers with respect to the
purchase of any of the Purchased Units or the consummation of the transaction
contemplated by this Agreement.

 14
 

Section 4.08           Legend.  It is understood that the certificates
evidencing the Purchased Units may bear the following legend:  “THIS
SECURITY HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED
(THE ‘SECURITIES ACT’), AND MAY NOT BE OFFERED OR SOLD, UNLESS IT HAS BEEN
REGISTERED UNDER THE SECURITIES ACT OR UNLESS AN EXEMPTION FROM REGISTRATION IS
AVAILABLE (AND, IN SUCH CASE, AN OPINION OF COUNSEL REASONABLY SATISFACTORY TO
THE PARTNERSHIP SHALL HAVE BEEN DELIVERED TO THE PARTNERSHIP TO THE EFFECT THAT
SUCH OFFIER OR SALE IS NOT REQUIRED TO BE REGISTERED UNDER THE SECURITIES ACT).”

Section 4.09           No Side Agreements.  There are no other agreements by, among or
between such Purchaser and any of its Affiliates, on the one hand, and any of
the other Purchasers or their Affiliates, on the other hand, with respect to
the transactions contemplated hereby nor promises or inducements for future
transactions between or among any of such parties.

ARTICLE V

COVENANTS

Section 5.01           Certain Special Allocations of
Book and Taxable Income.  To the
extent that the Unit Price is less than the trading price of the Common Units
on the American Stock Exchange as of the Closing Date, the General Partner
intends to specially allocate items of book and taxable income to the
Purchasers so that their capital accounts in their Units are consistent, on a
per-Unit basis, with the capital accounts of the other holders of Common Units
(and thus to assure fungibility of all Common Units).  Such special allocation will occur upon the
earlier to occur of any taxable period of MarkWest ending upon, or after, (i) a
book-up event or book-down event in accordance with Treasury Regulation Section
1.704-1(b)(2)(iv)(f) or a sale of all or substantially all of the assets of
MarkWest occurring after the date of the issuance of the Common Units or (ii)
the transfer of the Common Units to a Person that is not an Affiliate of the
holder.  A Purchaser holding a Common
Unit shall be required to provide notice to the General Partner of the transfer
of a Common Unit to a Person that is not an Affiliate of the Purchaser no later than the last Business
Day of the calendar year during which such transfer occurred, unless by virtue
of the application of clause (i) above, the General Partner has determined that
the Common Units are consistent, on a per-Unit basis, with the capital accounts
of the other holders of Common Units.

ARTICLE VI

MISCELLANEOUS

Section 6.01           Interpretation and Survival of
Provisions.  Article, Section,
Schedule, and Exhibit references are to this Agreement, unless otherwise
specified.  All references to
instruments, documents, contracts, and agreements are references to such
instruments, documents, contracts, and agreements as the same may be amended,
supplemented, and otherwise modified from time to time, unless otherwise
specified.  All references to a party in
this Agreement shall include such party’s successors and permitted
assigns.  The word “including” shall mean
“including but not limited to.”  The
terms “will” and “shall” shall be interpreted to have the same meaning.  Words in the singular form will be construed
to include 

 15
 

the plural and vice versa, unless the context
otherwise requires.  The section headings
contained in this Agreement are inserted for convenience only and will not
affect in any way the meaning or interpretation of this Agreement.  Whenever MarkWest has an obligation under the
Basic Documents, the expense of complying with that obligation shall be an
expense of MarkWest unless otherwise specified. Whenever any determination,
consent, or approval is to be made or given by a Purchaser, such action shall be
in such Purchaser’s sole discretion unless otherwise specified in this
Agreement.  If any provision in the Basic
Documents is held to be illegal, invalid, not binding, or unenforceable, such
provision shall be fully severable and the Basic Documents shall be construed
and enforced as if such illegal, invalid, not binding, or unenforceable
provision had never comprised a part of the Basic Documents, and the remaining
provisions shall remain in full force and effect.  The Basic Documents have been reviewed and
negotiated by sophisticated parties with access to legal counsel and shall not
be construed against the drafter.  The
representations and warranties set forth in Sections 3.01, 3.02, 3.06, 3.07,
3.08, 3.12, 3.13, 4.01, 4.02, 4.03, 4.04, 4.05, 4.06, 4.07 and 4.09 hereunder
shall survive the execution and delivery of this Agreement indefinitely, and
the other representations and warranties set forth herein shall survive for a
period of twelve (12) months following the Closing Date regardless of any investigation
made by or on behalf of MarkWest or each of the Purchasers.  The covenants made in this Agreement or any
other Basic Document shall survive the Closing of the transactions described
herein and remain operative and in full force and effect regardless of
acceptance of any of the Purchased Units and payment therefor and repayment or
repurchase thereof.  All indemnification
obligations of MarkWest and the provisions of Section 6.02 shall remain
operative and in full force and effect unless such obligations are expressly
terminated in a writing executed by all the parties to this Agreement
referencing that individual Section, regardless of any purported general
termination of this Agreement.

Section 6.02           Indemnification, Costs and
Expenses.

(a)           Indemnification by MarkWest.  MarkWest agrees to indemnify each Purchaser
and its officers, directors, employees and agents (collectively, the “Purchaser
Related Parties”) from, and hold each of them harmless against any and all
actions, suits, proceedings (including any investigations, litigation or
inquiries), demands, and causes of action, and, in connection therewith, and
promptly upon demand, pay or reimburse each of them for all reasonable costs,
losses, liabilities, damages, or expenses of any kind or nature whatsoever,
including, without limitation, the reasonable fees and disbursements of counsel
and all other reasonable expenses incurred in connection with investigating,
defending or preparing to defend any such matter that may be incurred by them
or asserted against or involve any of them as a result of, arising out of, or
in any way related to (i) any actual or proposed use by MarkWest of the
proceeds of any sale of the Purchased Units or (ii) the breach of any of the
representations, warranties or covenants of MarkWest contained herein, provided
such claim for indemnification relating to a breach of a representation or
warranty is made prior to the expiration of such representation or warranty.

(b)           Indemnification by Purchasers.  Each Purchaser agrees, severally and not
jointly, to indemnify MarkWest, MarkWest GP and their officers, directors,
employees and agents (collectively, the “MarkWest Related Parties”)
from, and hold each of them harmless against any and all actions, suits,
proceedings (including any investigations, 

 16
 

litigation, or
inquiries), demands, and causes of action, and, in connection therewith, and
promptly upon demand, pay or reimburse each of them for all reasonable costs,
losses, liabilities, damages, or expenses of any kind or nature whatsoever,
including, without limitation, the reasonable fees and disbursements of counsel
and all other reasonable expenses incurred in connection with investigating,
defending or preparing to defend any such matter that may be incurred by them
or asserted against or involve any of them as a result of, arising out of, or
in any way related to the breach of any of the representations, warranties or
covenants of such Purchaser contained herein, provided such claim for
indemnification relating to a breach of the representations and warranties is
made prior to the expiration of such representations and warranties.

(c)           Indemnification Procedure.  Promptly after any MarkWest Related Party or
Purchaser Related Party (hereinafter, the “Indemnified Party”) has
received notice of any indemnifiable claim hereunder, or the commencement of
any action or proceeding by a third person, which the Indemnified Party
believes in good faith is an indemnifiable claim under this Agreement, the
Indemnified Party shall give the indemnitor

 17

(d)           hereunder (the “Indemnifying Party”)
written notice of such claim or the commencement of such action or proceeding,
but failure to so notify the Indemnifying Party will not relieve the
Indemnifying Party from any liability it may have to such Indemnified Party
hereunder except to the extent that the Indemnifying Party is materially
prejudiced by such failure. Such notice shall state the nature and the basis of
such claim to the extent then known.  The
Indemnifying Party shall have the right to defend and settle, at its own
expense and by its own counsel, any such matter as long as the Indemnifying
Party pursues the same diligently and in good faith. If the Indemnifying Party
undertakes to defend or settle, it shall promptly notify the Indemnified Party
of its intention to do so, and the Indemnified Party shall cooperate with the
Indemnifying Party and its counsel in all commercially reasonable respects in
the defense thereof and the settlement thereof. Such cooperation shall include,
but shall not be limited to, furnishing the Indemnifying Party with any books,
records and other information reasonably requested by the Indemnifying Party
and in the Indemnified Party’s possession or control.  Such cooperation of the Indemnified Party
shall be at the cost of the Indemnifying Party. 
After the Indemnifying Party has notified the Indemnified Party of its
intention to undertake to defend or settle any such asserted liability, and for
so long as the Indemnifying Party diligently pursues such defense, the
Indemnifying Party shall not be liable for any additional legal expenses
incurred by the Indemnified Party in connection with any defense or settlement
of such asserted liability; provided, however, that the
Indemnified Party shall be entitled (i) at its expense, to participate in the
defense of such asserted liability and the negotiations of the settlement
thereof and (ii) if (A) the Indemnifying Party has failed to assume the defense
and employ counsel or (B) if the defendants in any such action include both the
Indemnified Party and the Indemnifying Party and counsel to the Indemnified
Party shall have concluded that there may be reasonable defenses available to
the Indemnified Party that are different from or in addition to those available
to the Indemnifying Party or if the interests of the Indemnified Party
reasonably may be deemed to conflict with the interests of the Indemnifying
Party, then the Indemnified Party shall have the right to select a separate
counsel and to assume such legal defense and otherwise to participate in the
defense of such action, with the expenses and fees of such separate counsel and
other expenses related to such participation to be reimbursed by the
Indemnifying Party as incurred. 
Notwithstanding any other provision of this Agreement, the Indemnifying
Party shall not settle any indemnified claim without the consent of the
Indemnified Party, unless the settlement thereof imposes no liability or
obligation on, and includes a complete release from liability of, and does not
include any admission of wrongdoing or illegal conduct by the Indemnified
Party.

Section
6.03           No Waiver; Modifications
in Writing.

(a)           Delay.  No failure or delay on the part of any party
in exercising any right, power, or remedy hereunder shall operate as a waiver
thereof, nor shall any single or partial exercise of any such right, power, or
remedy preclude any other or further exercise thereof or the exercise of any
right, power, or remedy. The remedies provided for herein are cumulative and
are not exclusive of any remedies that may be available to a party at law or in
equity or otherwise.

 18
 

(b)           Specific Waiver.  Except as otherwise provided herein, no
amendment, waiver, consent, modification, or termination of any provision of
this Agreement or any other Basic Document shall be effective unless signed by
each of the parties hereto or thereto affected by such amendment, waiver,
consent, modification, or termination. 
Any amendment, supplement or modification of or to any provision of this
Agreement or any other Basic Document, any waiver of any provision of this
Agreement or any other Basic Document, and any consent to any departure by
MarkWest from the terms of any provision of this Agreement or any other Basic
Document shall be effective only in the specific instance and for the specific
purpose for which made or given. Except where notice is specifically required
by this Agreement, no notice to or demand on MarkWest in any case shall entitle
MarkWest to any other or further notice or demand in similar or other circumstances.

Section 6.04           Binding Effect; Assignment.

(a)           Binding Effect.  This Agreement shall be binding upon
MarkWest, each Purchaser, and their respective successors and permitted
assigns. Except as expressly provided in this Agreement, this Agreement shall not
be construed so as to confer any right or benefit upon any Person other than
the parties to this Agreement, and their respective successors and permitted
assigns.

(b)           Assignment of Purchased Units.  All or any portion of a Purchaser’s Purchased
Units purchased pursuant to this Agreement may be sold, assigned or pledged by
such Purchaser, subject to compliance with applicable securities laws, Section
2.07(b) and the Registration Rights Agreement.

(c)           Assignment of Rights.  All or any portion of the rights and
obligations of each Purchaser under this Agreement may not be transferred by
such Purchaser without the written consent of MarkWest, unless such transfer is
to an Affiliate of the Purchaser or in connection with a total return swap or
similar transaction with respect to the Purchased Units, in which case written
consent shall not be unreasonably withheld.

Section 6.05           Confidentiality.  Notwithstanding anything herein to the
contrary, to the extent a Purchaser has executed a confidentiality agreement in
favor of MarkWest, such Purchaser shall continue to remain bound by such
confidentiality agreement.  Disclosure of
Confidential Information will not be deemed to be a breach of this Section 5.05
if such disclosure is made with the consent of MarkWest or pursuant to a
subpoena or order issued by a court of competent jurisdiction or by a judicial
or administrative or legislative body or committee; provided, however,
that upon receipt by a Purchaser of any subpoena or order covering Confidential
Information of MarkWest, such Purchaser will promptly notify MarkWest of such
subpoena or order.

Section 6.06           Communications.  All notices and demands provided for
hereunder shall be in writing and shall be given by registered or certified
mail, return receipt requested, telecopy, regular mail, air courier
guaranteeing overnight delivery, electronic mail or personal delivery to the
following addresses:

 19
 

(a)                                  If
to MarkWest:

                                                1515
Arapahoe Street

Tower 2, Suite 700

Denver, CO  80202

Attention:  Nancy K. Buese

Facsimile:  (303) 925-9309

Email: nbuese@markwest.com

with a copy (which shall not constitute notice) to:

Vinson & Elkins L.L.P.

2500 First City Tower

1001 Fannin Street

Houston, Texas 77002

Attention:  David P. Oelman, Esq.

Facsimile:  (713) 615-5861

Email: doelman@velaw.com

(b)                                 If
to GPS Income Fund LP, GPS High Yield Equities Fund LP, GPS New

Equity Fund LP, GPS MLP Fund LP or Agile Performance Fund LLC:

c/o GPS Partners

100 Wilshire Blvd., Suite 900

Santa Monica, CA 90401

Attention: Jeff Farron

Phone: (310) 496-5365

Facsimile: (310) 496-5399

(c)                                  If
to The Cushing MLP Opportunity Fund I, LP:

Swank Capital, LLC

3300 Oak Lawn Ave., Suite 650

Dallas, TX 75219

Attn:  Daniel L. Spears

Facsimile: (214) 219-2353

(d)                                 If
to Kayne Anderson MLP Investment Company:

Kayne Anderson MLP Investment Company

1100 Louisiana Street, Suite 4550

Houston, Texas 77002

Attention: Kevin S. McCarthy

Facsimile: (713) 655-7359

(e)                                  If
to Royal Bank of Canada:

 20
 

Royal Bank of Canada

c/o Daniel Weinstein

One Liberty Plaza

Second Floor

New York, NY 10006

Phone: (212) 858-7245

Facsimile: (212) 858-6004

daniel.weinstein@rbccm.com

(f)                                    If
to Structured Finance Americas, LLC:

Structured Finance Americas, LLC

c/o Deutsche Bank Securities Inc.

60 Wall Street, 4th Floor

Attention: Nicholas Bozzuto

New York, NY 10005

Phone: (212) 250-6340

nicholas.bozzuto@db.com

(g)                                 If
to Tortoise Energy Infrastructure Corporation:

Tortoise Energy Infrastructure Corporation

10801 Mastin Blvd., Suite 222

Overland Park, KS  66210

Attention: Zach Hamel

(h)                                 If
to Tortoise Energy Capital Corporation:

Tortoise Energy Capital Corporation

10801 Mastin Blvd., Suite 222

Overland Park, KS  66210

Attention: Zach Hamel

(i)                                     If
to ZLP Fund, L.P.:

Daniel M. Lynch

10 Harborside Financial Center, Suite 301

Jersey City, NJ 07311

Phone: (212) 440-0741

lynch@zimmerlucas.com

or to such other address as MarkWest or such Purchaser may designate in
writing. All notices and communications shall be deemed to have been duly given
at the time delivered by hand, if personally delivered; upon actual receipt if
sent by registered or certified mail, return receipt requested, or regular
mail, if mailed; when receipt acknowledged, if sent via facsimile or electronic
mail; and upon actual receipt when delivered by an air courier guaranteeing
overnight delivery.

 21
 

Section 6.07           Removal
of Legend.  Any Purchaser may request
MarkWest to remove the legend described in Section 4.08 from the certificates
evidencing the Purchased Units by submitting to MarkWest such certificates,
together with an opinion of counsel to the effect that such legend is no longer
required under the Securities Act or applicable state laws, as the case may be;
provided, however, that no such opinion shall be required in the event a
Purchaser is effecting a sale of such Purchased Units pursuant to Rule 144
under the Securities Act or an effective registration statement.

Section 6.08           Entire
Agreement.  This Agreement, the other
Basic Documents and the other agreements and documents referred to herein are
intended by the parties as a final expression of their agreement and intended
to be a complete and exclusive statement of the agreement and understanding of
the parties hereto in respect of the subject matter contained herein and
therein. There are no restrictions, promises, warranties or undertakings, other
than those set forth or referred to herein or therein with respect to the
rights granted by MarkWest or any of its Affiliates or each of the Purchasers
or any of their Affiliates set forth herein or therein.  This Agreement, the other Basic Documents and
the other agreements and documents referred to herein supersede all prior
agreements and understandings between the parties with respect to such subject
matter.

Section 6.09           Governing
Law.  This Agreement will be
construed in accordance with and governed by the laws of the State of Delaware
without regard to principles of conflicts of laws.

Section 6.10           Execution
in Counterparts.  This Agreement may
be executed in any number of counterparts and by different parties hereto in
separate counterparts, each of which counterparts, when so executed and
delivered, shall be deemed to be an original and all of which counterparts,
taken together, shall constitute but one and the same Agreement.

Section 6.11           Expenses.  MarkWest hereby covenants and agrees to
reimburse the Purchasers for reasonable and documented legal expenses of Baker
Botts L.L.P. incurred in connection with the negotiation, execution, delivery
and performance of the Basic Documents and the transactions contemplated hereby
and thereby, up to $20,000.00.  Any
request for such reimbursement by Purchasers shall be accompanied by a detailed
invoice for such amount.  Any amount in
excess of $20,000.00, in the aggregate, shall be paid by Purchasers, pro rata,
based on their Purchase Price.  If any
action at law or equity is necessary to enforce or interpret the terms of the
Basic Documents, the prevailing party shall be entitled to reasonable attorney’s
fees, costs and necessary disbursements in addition to any other relief to
which such party may be entitled.

Section 6.12           Waiver
of Preemptive Right.  Other than the
obligation of MarkWest GP to make contributions to MarkWest as required by
Section 5.2 of the Partnership Agreement, MarkWest GP hereby waives (for
itself and on behalf of its Affiliates) its preemptive rights provided under
Section 5.9 of the Partnership Agreement with respect to the issuances of
Partnership Securities pursuant to this Agreement.

[The remainder of this page is intentionally left
blank.]

 22

IN WITNESS WHEREOF, the parties hereto execute this
Agreement, effective as of the date first above written.

	
   

  	
  MARKWEST ENERGY PARTNERS, L.P.

  
	
   

  	
   

  
	
   

  	
  By:

  	
  MarkWest Energy GP, L.L.C.,

  
	
   

  	
   

  	
  its general
  partner

  
	
   

  	
   

  
	
   

  	
   

  	
  By: 

  	
  /S/ NANCY K. BUESE

  	
   

  
	
   

  	
   

  	
   

  	
  Nancy K. Buese

  	
   

  
	
   

  	
   

  	
   

  	
  Chief Financial Officer

  	
   

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
  MARKWEST ENERGY GP, L.L.C.

  
	
   

  	
  (solely for the
  purpose of Section  6.12)

  
	
   

  	
   

  
	
   

  	
   

  	
  By: 

  	
  /S/ NANCY K. BUESE

  	
   

  
	
   

  	
   

  	
   

  	
  Nancy K. Buese

  	
   

  
	
   

  	
   

  	
   

  	
  Chief Financial Officer

  	
   

  

 

 

	
  

  	
  ZLP FUND, L.P.

  
	
   

  	
   

  
	
   

  	
  By:

  	
  Zimmer Lucas Partners, LLC,

  
	
   

  	
   

  	
  its General
  Partner

  
	
   

  	
   

  	
   

  
	
   

  	
   

  
	
   

  	
   

  	
  By:

  	
  /S/ DEVIN GEOGHEGAN

  	
   

  
	
   

  	
   

  	
   

  	
  Devin Geoghegan, Partner

  	
   

  

 

 

	
  

  	
  STRUCTURED FINANCE AMERICAS, LLC

  
	
   

  	
   

  
	
   

  	
   

  	
  By:

  	
  /S/ SUNIL HARIANI

  	
   

  
	
   

  	
   

  	
   

  	
  Sunil Hariani

  	
   

  
	
   

  	
   

  	
   

  	
  V.P.

  	
   

  
	
   

  	
   

  
	
   

  	
   

  	
  By:

  	
  /S/ ANDREA LEUNG

  	
   

  
	
   

  	
   

  	
   

  	
  Andrea Leung

  	
   

  
	
   

  	
   

  	
   

  	
  V.P.

  	
   

  

 

 

	
  

  	
  ROYAL BANK OF CANADA

  
	
   

  	
  by its agent

  
	
   

  	
   

  
	
   

  	
  RBC CAPITAL MARKETS
  CORPORATION

  
	
   

  	
   

  
	
   

  	
   

  	
  By: 

  	
  /S/ JOSEF MUSKATEL

  	
   

  
	
   

  	
   

  	
   

  	
  Josef Muskatel

  	
   

  
	
   

  	
   

  	
   

  	
  Director and Senior
  Counsel

  	
   

  
	
   

  	
   

  	
   

  	
   

  	
   

  
	
   

  	
   

  	
  By: 

  	
  /S/ STEVEN MILKE

  	
   

  
	
   

  	
   

  	
   

  	
  Steven Milke

  	
   

  
	
   

  	
   

  	
   

  	
  Managing Director

  	
   

  

 

 

	
  

  	
  THE CUSHING MLP
  OPPORTUNITY FUND I, LP

  
	
   

  	
   

  
	
   

  	
   

  	
  By: 

  	
  /S/ JERRY V. SWANK

  	
   

  
	
   

  	
   

  	
   

  	
  Jerry V. Swank

  	
   

  
	
   

  	
   

  	
   

  	
  Managing Partner

  	
   

  

 

 

	
  

  	
  GPS INCOME FUND LP

  
	
   

  	
   

  
	
   

  	
   

  	
  By: 

  	
  GPS Partners, LLC,
  its General Partner

  	
   

  
	
   

  	
   

  	
   

  	
   

  	
   

  
	
   

  	
   

  	
  By: 

  	
  /S/ STEVEN SUGARMAN

  	
   

  
	
   

  	
   

  	
   

  	
  Steven Sugarman,
  Partner

  	
   

  
	
   

  	
   

  	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  	
   

  	
   

  
	
   

  	
  GPS HIGH YIELD EQUITIES
  FUND LP

  
	
   

  	
   

  
	
   

  	
   

  	
  By: 

  	
  GPS Partners, LLC,
  its General Partner 

  
	
   

  	
   

  
	
   

  	
   

  	
  By: 

  	
  /S/ STEVEN SUGARMAN

  	
   

  
	
   

  	
   

  	
   

  	
  Steven Sugarman,
  Partner

  	
   

  
	
   

  	
   

  	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  	
   

  	
   

  
	
   

  	
  GPS NEW EQUITY FUND LP

  
	
   

  	
   

  	
   

  	
   

  	
   

  
	
   

  	
   

  	
  By:

  	
  GPS Partners, LLC,
  its General Partner 

  	
   

  
	
   

  	
   

  	
   

  	
   

  	
   

  
	
   

  	
   

  	
  By: 

  	
  /S/ STEVEN SUGARMAN

  	
   

  
	
   

  	
   

  	
   

  	
  Steven Sugarman,
  Partner

  	
   

  
	
   

  	
   

  	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  	
   

  	
   

  
	
   

  	
  GPS MLP FUND LP

  
	
   

  	
   

  	
   

  	
   

  	
   

  
	
   

  	
   

  	
  By: 

  	
  GPS Partners, LLC,
  its General Partner 

  	
   

  
	
   

  	
   

  	
   

  	
   

  	
   

  
	
   

  	
   

  	
  By: 

  	
  /S/ STEVEN SUGARMAN

  	
   

  
	
   

  	
   

  	
   

  	
  Steven Sugarman,
  Partner

  	
   

  
	
   

  	
   

  	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  	
   

  	
   

  
	
   

  	
  AGILE PERFORMANCE
  FUND LLC

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
  By: 

  	
  /S/ STEVEN SUGARMAN

  	
   

  
	
   

  	
   

  	
   

  	
  Steven Sugarman,
  Partner

  	
   

  

 

 

	
   

  	
  KAYNE ANDERSON MLP INVESTMENT  COMPANY 

  
	
   

  	
   

  
	
   

  	
   

  	
  By:

  	
  /S/ JAMES BAKER

  	
   

  
	
   

  	
   

  	
   

  	
  James Baker

  	
   

  
	
   

  	
   

  	
   

  	
  Vice President

  	
   

  

 

 

	
  

  	
  TORTOISE ENERGY
  INFRASTRUCTURE CORPORATION

  
	
   

  	
   

  
	
   

  	
   

  	
  By: 

  	
  /S/ TERRY MATLACK

  	
   

  
	
   

  	
   

  	
   

  	
  Terry Matlack,
  Managing Director

  	
   

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
  TORTOISE ENERGY CAPITAL
  CORPORATION

  
	
   

  	
   

  
	
   

  	
   

  	
  By: 

  	
  /S/ TERRY MATLACK

  	
   

  
	
   

  	
   

  	
   

  	
  Terry Matlack,
  Managing Director

  	
   

  

 

Exhibit A — Form
of Registration Rights Agreement

See Attached

Exhibit B —
Partnership Agreement and Certificate of Limited Partnership

See Attached

Exhibit C — Form
of Opinion of MarkWest Counsel

See Attached

Schedule 1.01

Cory Bromley

Nancy K. Buese

Randy S. Nickerson

Andrew L. Schroeder

Frank M. Semple

Schedule 2.02

	
  Purchaser

  	
   

  	
  Units Purchased

  	
   

  	
  Total Purchase Price

  	
   

  
	
   

  	
   

  	
   

  	
   

  	
   

  	
   

  
	
  Kayne Anderson MLP
  Investment Company

  	
   

  	
  303,215

  	
   

  	
  $

  	
  10,000,030.70

  	
   

  
	
  GPS Income Fund LP

  	
   

  	
  148,239

  	
   

  	
  $

  	
  4,888,922.22

  	
   

  
	
  GPS High Yield Equities
  Fund LP

  	
   

  	
  36,027

  	
   

  	
  $

  	
  1,188,170.46

  	
   

  
	
  GPS New Equity Fund LP

  	
   

  	
  268,027

  	
   

  	
  $

  	
  8,839,530.46

  	
   

  
	
  GPS MLP Fund LP

  	
   

  	
  22,739

  	
   

  	
  $

  	
  749,932.22

  	
   

  
	
  Agile Performance Fund
  LLC

  	
   

  	
  30,321

  	
   

  	
  $

  	
  999,986.58

  	
   

  
	
  Tortoise Energy
  Infrastructure Corporation

  	
   

  	
  121,286

  	
   

  	
  $

  	
  4,000,012.28

  	
   

  
	
  Tortoise Energy Capital
  Corporation

  	
   

  	
  181,929

  	
   

  	
  $

  	
  6,000,018.42

  	
   

  
	
  Royal Bank of Canada

  	
   

  	
  1,313,933

  	
   

  	
  $

  	
  43,333,510.34

  	
   

  
	
  Structured Finance
  Americas, LLC

  	
   

  	
  272,893

  	
   

  	
  $

  	
  9,000,011.14

  	
   

  
	
  The Cushing MLP
  Opportunity Fund I, LP

  	
   

  	
  1,212,857

  	
   

  	
  $

  	
  40,000,023.86

  	
   

  
	
  ZLP Fund, L.P.

  	
   

  	
  181,929

  	
   

  	
  $

  	
  6,000,018.42

  	
   

  
	
   

  	
   

  	
   

  	
   

  	
   

  	
   

  
	
  Total

  	
   

  	
  4,093,395

  	
   

  	
  $

  	
  135,000,167.10

  	
   

  

 

Schedule 3.02

MarkWest Energy Appalachia, L.L.C.

MarkWest Energy East Texas Gas Company, L.P.

MarkWest Energy Finance Corporation

MarkWest Energy Operating Company, L.L.C.

MarkWest Javelina Company

MarkWest Pinnacle L.P.

MarkWest Texas GP, L.L.C.

MW Texas Limited, L.L.C.

MarkWest Western Oklahoma Gas Company, L.L.C.Exhibit 10.2

REGISTRATION RIGHTS
AGREEMENT

by and among

MARKWEST ENERGY PARTNERS,
L.P.

AND

THE PURCHASERS PARTY
HERETO

REGISTRATION
RIGHTS AGREEMENT

THIS REGISTRATION RIGHTS AGREEMENT (this “Agreement”)
is made and entered into as of April 9, 2007, by and among MARKWEST ENERGY
PARTNERS, L.P. (“MarkWest”) and each of the purchasers set forth on
Schedule A hereto (each a “Purchaser” and collectively, the “Purchasers”).  Capitalized terms used herein without
definition shall have the meanings given to them in the Purchase Agreement.

This Agreement is made in connection with the Closing
of the issuance and sale of the Purchased Units pursuant to the Unit Purchase
Agreement, dated as of April 9, 2007, by and among MarkWest, MarkWest Energy
GP, L.L.C. and the Purchasers (the “Purchase Agreement”).  MarkWest has agreed to provide the
registration and other rights set forth in this Agreement for the benefit of
the Purchasers pursuant to Section 2.04(a)(iv) of the Purchase Agreement. In
consideration of the mutual covenants and agreements set forth herein and in
the Purchase Agreement and for good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged by each party hereto, the parties
hereby agree as follows:

ARTICLE I

DEFINITIONS

Section 1.01           Definitions.  The terms set forth below are used herein as
so defined:

“Affiliate” means, with respect to a specified
Person, any other Person, directly or indirectly controlling, controlled by or
under direct or indirect common control with such specified Person.  For purposes of this definition, “control”
(including, with correlative meanings, “controlling,” “controlled by,” and “under
common control with”) means the power to direct or cause the direction of the
management and policies of such Person, directly or indirectly, whether through
the ownership of voting securities, by contract or otherwise.

“Agreement” has the meaning specified therefor
in the introductory paragraph hereof.

“Business Day” means any day other than a
Saturday, Sunday, or a legal holiday for commercial banks in New York, New
York.

 “Commission”
means the United States Securities and Exchange Commission.

“Common Units” means the common units of
MarkWest.

“Effectiveness Period” has the meaning
specified therefor in Section 2.01(a) of this Agreement.

“Exchange Act” shall mean the Securities
Exchange Act of 1934, as amended from time to time, and the rules and
regulations of the Commission promulgated thereunder.

“Holder” means the record holder of any
Registrable Securities.

“Included Registrable Securities” has the
meaning specified therefor in Section 2.02(a) of this Agreement.

 1
 

“Liquidated Damages Amount” means an amount
equal to 0.25% of the product of $32.98 times the number of Registrable
Securities held by such Holder per 30-day period for the first sixty (60) days,
with such payment amount increasing by an additional 0.25% of the product of
$32.98 times the number of Registrable Securities held by such Holder per
30-day period for each subsequent sixty (60) days, up to a maximum of 1.00% of
the product of $32.98 times the number of Registrable Securities held by such
Holder per 30-day period.  The Liquidated
Damages Amount for any period of less than 30 days shall be prorated by
multiplying the Liquidated Damages Amount to be paid in a full 30-day period by
a fraction, the numerator of which is the number of days for which such
liquidated damages are owed, and the denominator of which is 30.

“Losses” has the meaning specified therefor in
Section 2.08(a) of this Agreement.

“Managing Underwriter” means, with respect to
any Underwritten Offering, the book running lead manager of  such Underwritten Offering.

“MarkWest” has the meaning specified therefor
in the introductory paragraph of this Agreement.

“MarkWest Hydrocarbon” means MarkWest
Hydrocarbon, Inc., a Delaware corporation.

“Opt Out Notice”  has the meaning specified therefor in Section
2.02(a).

“Person” means any individual, corporation,
company, voluntary association, partnership, joint venture, trust, limited
liability company, unincorporated organization, government or any agency,
instrumentality or political subdivision thereof, or any other form of entity.

“Piggyback Registration” has the meaning
specified therefor in Section 2.02(a) of this Agreement.

“Prior Holders” means each investor party to
the Registration Rights Agreement dated November 9, 2005, by and among MarkWest
and each party listed on Schedule A thereto and each investor party to the
Registration Rights Agreement dated December 23, 2005 by and among MarkWest and
each party listed on Schedule A thereto.

“Purchase Agreement” has the meaning specified
therefor in the introductory paragraph of this Agreement.

“Purchased Units”  shall have the meaning set forth in the
Purchase Agreement.

“Purchaser” and “Purchasers” each has
the meaning specified therefor in the introductory paragraph of this Agreement.

“Registrable Securities” means the Common Units
comprising the Purchased Units until such time as such securities cease to be
Registrable Securities pursuant to Section 1.02 hereof.

“Registration Expenses” has the meaning
specified therefor in Section 2.07(a) of this Agreement.

 2
 

“Securities Act” means the Securities Act of
1933, as amended from time to time, and the rules and regulations of the
Commission promulgated thereunder.

“Selling Expenses” has the meaning specified
therefor in Section 2.07(a) of this Agreement.

“Selling Holder” means a Holder who is selling
Registrable Securities pursuant to a registration statement.

“Selling Holder Indemnified Person” has the
meaning specified in Section 2.08(a) of this Agreement.

“Shelf Registration” has the meaning specified
therefor in Section 2.01(a) of this Agreement.

“Shelf Registration Statement” has the meaning
specified therefor in Section 2.01(a) of this Agreement.

“Underwritten Offering” means an offering
(including an offering pursuant to a Shelf Registration Statement) in which
Common Units are sold to an underwriter on a firm commitment basis for
reoffering to the public or an offering that is a “bought deal” with one or
more investment banks.

Section 1.02           Registrable Securities.  Any Registrable Security will cease to be a
Registrable Security when (a) a registration statement covering such
Registrable Security becomes or is declared effective by the Commission and
such Registrable Security has been sold or disposed of pursuant to such
effective registration statement; (b) such Registrable Security has been
disposed of pursuant to any section of Rule 144 (or any similar provision then
in force) under the Securities Act; (c) such Registrable Security is held by
MarkWest or one of its subsidiaries; or (d) such Registrable Security has been
sold in a private transaction in which the transferor’s rights under this
Agreement are not assigned to the transferee of such securities pursuant to
Section 2.10 hereof.

Section 1.03           Rights and Obligations.  Except for the rights and obligations under
Section 2.08 herein, all rights and obligations of each Purchaser under this
Agreement, and all rights and obligations of MarkWest under this Agreement with
respect to such Purchaser, shall terminate when such Purchaser is no longer a
Holder.

ARTICLE II

REGISTRATION RIGHTS

Section 2.01           Shelf Registration.

(a)           Shelf Registration.  As soon as practicable following the Closing
of the purchase of the Purchased Units pursuant to the terms of the Purchase
Agreement, but in any event within 30 days of the Closing, MarkWest shall
prepare and file a registration statement under the Securities Act to permit
the public resale of the Registrable Securities from time to time as permitted
by Rule 415 under the Securities Act (the “Shelf Registration Statement”).  MarkWest

 3
 

shall use its
commercially reasonable efforts to cause the Shelf Registration Statement to
become effective no later than 120 days after the Closing Date (the “Shelf
Registration”).  A Shelf Registration
Statement filed pursuant to this Section 2.01(a) shall be on such appropriate
registration form of the Commission as shall be selected by MarkWest; provided,
however, that if a prospectus supplement will be used in connection with
the marketing of an Underwritten Offering from the Shelf Registration Statement
and the Managing Underwriter at any time shall notify MarkWest in writing that,
in the sole judgment of such Managing Underwriter, inclusion of detailed
information to be used in such prospectus supplement is of material importance
to the success of the Underwritten Offering of such Registrable Securities,
MarkWest shall use its commercially reasonable efforts to include such
information in the prospectus.  MarkWest
will cause the Shelf Registration Statement filed pursuant to this Section
2.01(a) to be continuously effective, supplemented and amended to the extent
necessary to assure that it is available for resale of all Registrable
Securities by the Holders and that it conforms in all material respects with
the requirements of the Securities Act during the entire period beginning on
the date the Shelf Registration Statement first is declared effective under the
Securities Act and ending on the earlier to occur of (i) the date all
Registrable Securities covered by the Shelf Registration Statement have been
distributed in the manner set forth and as contemplated in the Shelf
Registration Statement and (ii) the date on which the Registrable Securities
cease to be Registrable Securities hereunder in accordance with Section 1.02
(the “Effectiveness Period”).  The
Shelf Registration Statement when declared effective (including the documents
incorporated therein by reference) will comply as to form with all applicable
requirements of the Securities Act and the Exchange Act and will not contain an
untrue statement of a material fact or omit to state a material fact required
to be stated therein or necessary to make the statements therein not
misleading.  As soon as practicable
following the date that the Shelf Registration Statement becomes effective, but
in any event, within five Business Days of such date, MarkWest shall provide
the Purchasers with written notice of the effectiveness of the Shelf
Registration Statement.

(b)           Delay Rights.  Notwithstanding anything to the contrary
contained herein, MarkWest may, upon written notice to any Selling Holder whose
Registrable Securities are included in the Shelf Registration Statement,
suspend such Selling Holder’s use of any prospectus which is a part of the
Shelf Registration Statement (in which event the Selling Holder shall
discontinue sales of the Registrable Securities pursuant to the Shelf
Registration Statement), for a period not to exceed an aggregate of 60 days in
any 180-day period and not to exceed an aggregate of 90 days in any 365-day
period, if (i) MarkWest is pursuing a material acquisition, merger,
reorganization, disposition or other similar transaction and MarkWest
determines in good faith that MarkWest’s ability to pursue or consummate such a
transaction would be materially adversely affected by any required disclosure
of such transaction in the Shelf Registration Statement or (ii) MarkWest has
experienced some other material non-public event the disclosure of which at
such time, in the good faith judgment of MarkWest, would materially adversely
affect MarkWest.  Upon disclosure of such
information or the termination of the condition described above, MarkWest shall
provide prompt written notice to the Selling Holders whose Registrable
Securities are included in the Shelf Registration Statement, and shall promptly
terminate any suspension of sales it has put into effect and shall take such
other actions to permit registered sales of Registrable Securities as
contemplated in this Agreement.

 4
 

(c)           Delay in Effectiveness of Shelf
Registration Statement; Certain Suspensions.

(i)            If the Shelf Registration Statement
does not become or is not declared effective within 120 days after Closing,
then, until such time as the Shelf Registration Statement is declared effective
or there are no longer any Registrable Securities outstanding, MarkWest shall
pay each Holder with respect to any such failure, following the 120th day after the Closing, an amount equal to the
Liquidated Damages Amount, as liquidated damages and not as a penalty.  

(ii)           If (A) the Holders shall be prohibited from selling their Registrable
Securities under the Shelf Registration Statement as a result of a suspension
pursuant to Section 2.01(b) in excess of the periods permitted therein,
MarkWest shall pay the Holders an amount equal to the Liquidated Damages
Amount, commencing 10 days from the date on which the suspension period
exceeded the permitted period; or (B) the Shelf Registration Statement is filed
and declared effective but, during the Effectiveness Period, shall thereafter
cease to be effective or fail to be usable for its intended purpose, then until
the suspension is lifted or a post-effective amendment, supplement or report is
declared effective with the Commission, but not including any day on which a
suspension is lifted or such amendment, supplement or report is declared
effective, MarkWest shall pay the Holders an amount equal to the Liquidated
Damages Amount, commencing 10 days from the date on which the Shelf
Registration Statement ceased to be effective or failed to be useable for its
intended purposes, as liquidated damages and not as a penalty.  For purposes of this Section 2.01(c), a
suspension shall be deemed lifted on the date that notice that the suspension
has been lifted is delivered to the Holders pursuant to Section 3.01 of this
Agreement.

(iii)          The Liquidated Damages Amount shall be
paid to each Holder in cash within ten Business Days of the end of each such
30-day period.  Any payments made
pursuant to this Section 2.01(c) shall constitute the Holders’ exclusive remedy
for such events.  The Liquidated Damages
Amount imposed hereunder shall be made to the Holders in immediately available
funds.

(iv)          The Holders’ rights under this Section
2.01(c) shall terminate when such Registrable Securities become eligible for
resale under Rule 144(k) (or any similar provision then in force) under the
Securities Act.

Section 2.02           Piggyback
Registration.

(a)           Participation.  If MarkWest, MarkWest Hydrocarbon or any
subsidiary of MarkWest Hydrocarbon at any time proposes to (i) file a prospectus
supplement to an effective shelf registration statement with respect to an
Underwritten Offering of Common Units, (ii) register any Common Units for
its own account for sale to the public in an Underwritten Offering other than,
in the case of this clause (ii), (a) a registration relating solely
to employee benefit plans, (b) a registration relating solely to a
Rule 145 transaction, or (c) a registration on any registration form
which does not permit secondary sales, or (iii) register any Common Units on
behalf of any other person for the sale of Common Units in an Underwritten
Offering, then, as soon as practicable following the engagement of counsel by
MarkWest to prepare the documents

 5
 

to be used in
connection with an Underwritten Offering, MarkWest shall give written notice of
such proposed Underwritten Offering to the Holders and such notice shall offer
the Holders the opportunity to include in such Underwritten Offering such
number of Registrable Securities as each such Holder may request in writing (a “Piggyback
Registration”); provided, however, that MarkWest shall not be required to
offer such opportunity to Holders to the extent MarkWest has been advised by
the Managing Underwriter that the inclusion of Registrable Securities for sale
for the benefit of the Holders will have a materially adverse effect on the
price, timing or distribution of the Common Units.  The notice required to be provided in this
Section 2.02(a) to Holders shall be provided on a Business Day pursuant to
Section 3.01 hereof and receipt of such notice shall be confirmed by the
Holder.  Subject to Section 2.02(b),
MarkWest shall include in such Underwritten Offering all such Registrable
Securities (“Included Registrable Securities”) with respect to which
MarkWest has received requests within one Business Day after MarkWest’s notice
has been delivered in accordance with Section 3.01.  If no request for inclusion from a Holder is
received within the specified time, such Holder shall have no further right to
participate in such Piggyback Registration. 
If, at any time after giving written notice of its intention to
undertake an Underwritten Offering and prior to the closing of such
Underwritten Offering, MarkWest shall determine for any reason not to undertake
or to delay such Underwritten Offering, MarkWest may, at its election, give
written notice of such determination to the Selling Holders and, (i) in
the case of a determination not to undertake such Underwritten Offering, shall
be relieved of its obligation to sell any Included Registrable Securities in
connection with such terminated Underwritten Offering, and (ii) in the
case of a determination to delay such Underwritten Offering, shall be permitted
to delay offering any Included Registrable Securities for the same period as
the delay in the Underwritten Offering. Any Selling Holder shall have the right
to withdraw such Selling Holder’s request for inclusion of such Selling Holder’s
Registrable Securities in such Underwritten Offering by giving written notice
to MarkWest of such withdrawal up to and including the time of pricing of such
Underwritten Offering.  No Holders shall
be entitled to participate in any such Underwritten Offering under this Section
2.02(a) unless such Holder (together with any Affiliate that owns Registrable
Securities and is a Selling Holder) holds at least $5 million of Registrable
Securities in such offering (determined by multiplying the number of
Registrable Securities owned by the average of the closing price for Common
Units for the ten (10) trading days preceding the date of such notice).  Notwithstanding the foregoing, any Holder may
deliver written notice (an “Opt Out Notice”) to the Company requesting
that such Holder not receive notice from the Company of any proposed
Underwritten Offering; provided that any such Holder may later revoke any such
notice.

(b)           Priority of Piggyback Registration.  If the Managing Underwriter or Underwriters
of any proposed Underwritten Offering of Common Units included in a Piggyback
Registration advises MarkWest in writing that the total amount of Common Units
which the Selling Holders and any other Persons intend to include in such
Underwritten Offering exceeds the number which can be sold in such offering
without being likely to have a materially adverse effect on the price, timing
or distribution of the Common Units offered or the market for the Common Units,
then the Common Units to be included in such Underwritten Offering shall
include the number of Registrable Securities that such Managing Underwriter or Underwriters
advises MarkWest can be sold without having such materially adverse effect,
with such number to be allocated pro  rata among the Selling
Holders and Prior Holders who have requested participation in the Piggyback
Registration (based, for each such Selling Holder or Prior Holder, as
applicable, on

 6
 

the percentage derived by
dividing (A) the number of Registrable Securities, or other registrable
securities entitled to be included in a Piggyback Registration, proposed to be
sold by such Selling Holder or Prior Holder in such offering; by (B) the
aggregate number of Common Units proposed to be sold by, as the case may be,
the Selling Holders and Prior Holders participating in the Piggyback
Registration to be included in such offering).

(c)           Termination of Piggyback
Registration Rights.  The Piggyback
Registration rights granted pursuant to this Section 2.02 shall be unlimited in
number and shall terminate the later of (i) two years following the Closing
Date and (ii) the date on which all Registrable Securities cease to be
Registrable Securities hereunder in accordance with Section 1.02.

Section 2.03           Underwritten Offering.

(a)           Shelf Registration.  In the event that one or more Selling Holders
elect to dispose of Registrable Securities under the Shelf Registration
Statement pursuant to an Underwritten Offering and such Selling Holders
reasonably anticipate gross proceeds from such Underwritten Offering of at
least twenty million dollars ($20,000,000), in the aggregate (determined by
multiplying the number of Registrable Securities owned by the average of the
closing price for Common Units for the ten (10) trading days preceding the date
of such notice), MarkWest shall enter into an underwriting agreement in
customary form with the Managing Underwriter or Underwriters, which shall
include, among other provisions, indemnities to the effect and to the extent
provided in Section 2.08, and shall take all such other reasonable actions as
are requested by the Managing Underwriter in order to expedite or facilitate the
registration and disposition of the Registered Securities; provided, however,
that  MarkWest shall be required to cause
appropriate officers of MarkWest or its Affiliates to participate in a “road
show” or similar marketing effort being conducted by such underwriter with
respect to such Underwritten Offering only if the Selling Holders reasonably
anticipate gross proceeds from such Underwritten Offering of at least forty
million dollars ($40,000,000) (determined by multiplying the number of
Registrable Securities owned by the average of the closing price for Common
Units for the ten (10) trading days preceding the date of such notice).

(b)           General Procedures.  In connection with any Underwritten Offering
under this Agreement (except for Underwritten Offerings pursuant to Section
2.03(a)), MarkWest shall be entitled to select the Managing Underwriter or
Underwriters, each of which must be a nationally-recognized firm.  In the case of an Underwritten Offering
pursuant to Section 2.03(a) hereof, the Selling Holders in such Underwritten
Offering shall be entitled to select the Managing Underwriter or Underwriters,
each of which must be a nationally recognized firm.  In the event there is more than one Selling
Holder, each Selling Holder shall be entitled to vote for the selection of the
Managing Underwriter and shall be entitled to the number of votes equal to the
number of Registrable Securities being offered for sale pursuant to such
Underwritten Offering, with the majority vote of such Selling Holders determining
the Managing Underwriter.  In connection
with an Underwritten Offering under Section 2.01 or 2.02 hereof, each Selling
Holder and MarkWest shall be obligated to enter into an underwriting agreement
which contains such representations, covenants, indemnities and other rights
and obligations as are customary in underwriting agreements for firm commitment
offerings  of securities.  No Selling Holder may participate in such
Underwritten Offering unless such Selling Holder agrees to sell its Registrable
Securities on the basis provided in such underwriting agreement and completes
and

 7
 

executes all
questionnaires, powers of attorney, indemnities and other documents reasonably
required under the terms of such underwriting agreement.  Each Selling Holder may, at its option,
require that any or all of the representations and warranties by, and the other
agreements on the part of, MarkWest to and for the benefit of such underwriters
also be made to and for such Selling Holder’s benefit and that any or all of
the conditions precedent to the obligations of such underwriters under such
underwriting agreement also be conditions precedent to its obligations. No
Selling Holder shall be required to make any representations or warranties to
or agreements with MarkWest or the underwriters other than representations,
warranties or agreements regarding such Selling Holder and its ownership of the
securities being registered on its behalf and its intended method of
distribution and any other representation required by law.  If any Selling Holder disapproves of the
terms of an underwriting, such Selling Holder may elect to withdraw therefrom
by notice to MarkWest and the Managing Underwriter; provided, however,
that such withdrawal must be made prior to the time in the second to last
sentence of Section 2.02(a) hereof to be effective.  No such withdrawal or abandonment shall
affect MarkWest’s obligation to pay Registration Expenses.

Section 2.04           Registration Procedures.  In connection with its obligations contained
in Sections 2.01, 2.02 and 2.03, MarkWest will, as expeditiously as possible:

(a)           prepare and file with the Commission
such amendments and supplements to the Shelf Registration Statement and the
prospectus used in connection therewith as may be necessary to keep the Shelf
Registration Statement effective for the Effectiveness Period and as may be
necessary to comply with the provisions of the Securities Act with respect to
the disposition of all securities covered by the Shelf Registration Statement;

(b)           furnish to each Selling Holder (i) as
far in advance as reasonably practicable before filing the Shelf Registration
Statement or any other registration statement contemplated by this Agreement or
any supplement or amendment thereto, upon request, copies of reasonably complete
drafts of all such documents proposed to be filed (including exhibits and each
document incorporated by reference therein to the extent then required by the
rules and regulations of the Commission), and provide each such Selling Holder
the opportunity to object to any information pertaining to such Selling Holder
and its plan of distribution that is contained therein and make the corrections
reasonably requested by such Selling Holder with respect to such information
prior to filing the Shelf Registration Statement or such other registration
statement or supplement or amendment thereto, and (ii) such number of copies of
the Shelf Registration Statement or such other registration statement and the
prospectus included therein and any supplements and amendments thereto as such
Selling Holders may reasonably request in order to facilitate the public sale
or other disposition of the Registrable Securities covered by such Shelf
Registration Statement or other registration statement;

(c)           if applicable, use its commercially
reasonable efforts to register or qualify the Registrable Securities covered by
the Shelf Registration Statement or any other registration statement
contemplated by this Agreement under the securities or blue sky laws of such
jurisdictions as the Selling Holders or, in the case of an Underwritten
Offering, the Managing Underwriter, shall reasonably request, provided that
MarkWest will not be required to qualify generally to transact business in any
jurisdiction where it is not then required to so qualify or to

 8
 

take any action which
would subject it to general service of process in any such jurisdiction where
it is not then so subject;

(d)           promptly notify each Selling Holder
and each underwriter, at any time when a prospectus relating thereto is required
to be delivered under the Securities Act, of (i) the filing of the Shelf
Registration Statement or any other registration statement contemplated by this
Agreement or any prospectus or prospectus supplement to be used in connection
therewith, or any amendment or supplement thereto, and, with respect to such
Shelf Registration Statement or any other registration statement or any
post-effective amendment thereto, when the same has become effective; and (ii)
any written comments from the Commission with respect to any filing referred to
in clause (i) and any written request by the Commission for amendments or
supplements to the Shelf Registration Statement or any other registration
statement or any prospectus or prospectus supplement thereto;

(e)           immediately notify each Selling
Holder and each underwriter, at any time when a prospectus relating thereto is
required to be delivered under the Securities Act, of (i) the happening of any
event as a result of which the prospectus or prospectus supplement contained in
the Shelf Registration Statement or any other registration statement
contemplated by this Agreement, as then in effect, includes an untrue statement
of a material fact or omits to state any material fact required to be stated
therein or necessary to make the statements therein not misleading in the light
of the circumstances then existing; (ii) the issuance or threat of issuance by
the Commission of any stop order suspending the effectiveness of the Shelf
Registration Statement or any other registration statement contemplated by this
Agreement, or the initiation of any proceedings for that purpose; or (iii) the
receipt by MarkWest of any notification with respect to the suspension of the
qualification of any Registrable Securities for sale under the applicable
securities or blue sky laws of any jurisdiction.  Following the provision of such notice,
MarkWest agrees to as promptly as practicable amend or supplement the
prospectus or prospectus supplement or take other appropriate action so that
the prospectus or prospectus supplement does not include an untrue statement of
a material fact or omit to state a material fact required to be stated therein
or necessary to make the statements therein not misleading in the light of the
circumstances then existing and to take such other action as is necessary to
remove a stop order, suspension, threat thereof or proceedings related thereto;

(f)            furnish to each Selling Holder
copies of any and all transmittal letters or other correspondence with the
Commission or any other governmental agency or self-regulatory body or other
body having jurisdiction (including any domestic or foreign securities
exchange) relating to such offering of Registrable Securities;

(g)           in the case of an Underwritten
Offering, furnish upon request to a Selling Holder, (i) an opinion of counsel
for MarkWest, dated the effective date of the applicable registration statement
or the date of any amendment or supplement thereto, and a letter of like kind
dated the date of the closing under the underwriting agreement, and (ii) a “cold
comfort” letter, dated the effective date of the applicable registration
statement or the date of any amendment or supplement thereto and a letter of
like kind dated the date of the closing under the underwriting agreement, in
each case, signed by the independent public accountants who have certified
MarkWest’s financial statements included or incorporated by reference into the
applicable registration statement, and each of the opinion and the “cold
comfort” letter shall be in

 9
 

customary form and
covering substantially the same matters with respect to such registration
statement (and the prospectus and any prospectus supplement included therein)
and as are customarily covered in opinions of issuer’s counsel and in accountants’
letters delivered to the underwriters in Underwritten Offerings of securities,
such other matters as such underwriters may reasonably request;

(h)           otherwise use its commercially
reasonable efforts to comply with all applicable rules and regulations of the
Commission, and make available to its security holders, as soon as reasonably
practicable, an earnings statement covering the period of at least 12 months,
but not more than 18 months, beginning with the first full calendar month after
the effective date of such registration statement, which earnings statement
shall satisfy the provisions of Section 11(a) of the Securities Act and
Rule 158 promulgated thereunder;

(i)            make available to the appropriate
representatives of the Managing Underwriter and Selling Holders access to such
information and MarkWest personnel as is reasonable and customary to enable
such parties to establish a due diligence defense under the Securities Act;
provided that MarkWest need not disclose any information to any such representative
unless and until such representative has entered into a confidentiality
agreement with MarkWest;

(j)            cause all such Registrable
Securities registered pursuant to this Agreement to be listed on each
securities exchange or nationally recognized quotation system on which similar
securities issued by MarkWest are then listed;

(k)           use its commercially reasonable
efforts to cause the Registrable Securities to be registered with or approved
by such other governmental agencies or authorities as may be necessary by
virtue of the business and operations of MarkWest to enable the Selling Holders
to consummate the disposition of such Registrable Securities;

(l)            provide a transfer agent and
registrar for all Registrable Securities covered by such registration statement
not later than the effective date of such registration statement; and

(m)          enter into customary agreements and
take such other actions as are reasonably requested by the Selling Holders or
the underwriters, if any, in order to expedite or facilitate the disposition of
such Registrable Securities.

Each Selling Holder, upon
receipt of notice from MarkWest of the happening of any event of the kind
described in subsection (e) of this Section 2.04, shall forthwith discontinue
disposition of the Registrable Securities until such Selling Holder’s receipt
of the copies of the supplemented or amended prospectus contemplated by
subsection (e) of this Section 2.04 or until it is advised in writing by
MarkWest that the use of the prospectus may be resumed, and has received copies
of any additional or supplemental filings incorporated by reference in the
prospectus, and, if so directed by MarkWest, such Selling Holder will, or will
request the managing underwriter or underwriters, if any, to deliver to
MarkWest (at MarkWest’s expense) all copies in their possession or control,
other than permanent file copies then in such Selling Holder’s possession, of
the prospectus covering such Registrable Securities current at the time of
receipt of such notice.

 10

Section 2.05           Cooperation by Holders.  MarkWest shall have no obligation to include
Registrable Securities of a Holder in the Shelf Registration Statement or in a
Piggyback Registration who has failed to timely furnish such information which,
in the opinion of counsel to MarkWest, is reasonably required in order for the
registration statement or prospectus supplement, as applicable, to comply with
the Securities Act.

Section 2.06           Restrictions on Public Sale by
Holders of Registrable Securities. 
Each Holder of Registrable Securities who is included in the Shelf
Registration Statement agrees not to effect any public sale or distribution of
Registrable Securities during the 30 calendar day period beginning on the date
of a prospectus supplement or prospectus filed with the Commission with respect
to the pricing of an Underwritten Offering, provided that the duration of the
foregoing restrictions shall be no longer than the duration of the shortest
restriction generally imposed by the underwriters on the officers or directors
or any other unitholder of MarkWest on whom a restriction is imposed; and
provided further, that the restrictions under this Section 2.06 shall not apply
(i) to any Holder that is not otherwise eligible to participate in such
Underwritten Offering pursuant to Section 2.02(a), (ii) to the sale or
distribution of Registrable Securities in such Underwritten Offering pursuant
to Section 2.02(a) or (iii) has submitted an Opt Out Notice.

Section 2.07           Expenses.

(a)           Certain Definitions.  “Registration Expenses” means all
expenses incident to MarkWest’s performance under or compliance with this
Agreement to effect the registration of Registrable Securities in a Shelf
Registration or a Piggyback Registration, or otherwise pursuant to Section
2.03, and the disposition of such securities, including, without limitation,
all registration, filing, securities exchange listing and American Stock
Exchange or other securities exchange or listing fees, all registration,
filing, qualification and other fees and expenses of complying with securities
or blue sky laws, fees of the National Association of Securities Dealers, Inc.,
transfer taxes and fees of transfer agents and registrars, all word processing,
duplicating and printing expenses, the fees and disbursements of counsel and
independent public accountants for MarkWest, including the expenses of any
special audits or “cold comfort” letters required by or incident to such
performance and compliance.  Except as
otherwise provided in Section 2.08 hereof, MarkWest shall not be responsible
for legal fees incurred by Holders in connection with the exercise of such
Holders’ rights hereunder.  In addition,
MarkWest shall not be responsible for any “Selling Expenses,” which
means all underwriting fees, discounts and selling commissions allocable to the
sale of the Registrable Securities.

(b)           Expenses.  MarkWest will pay all Registration Expenses
in connection with the Shelf Registration Statement filed pursuant to Section
2.01(a) of this Agreement, and MarkWest will pay all Registration Expenses in
connection with a Piggyback Registration, whether or not the applicable
registration statement becomes effective or any sale is made pursuant to the
Shelf Registration Statement or Piggyback Registration. Each Selling Holder shall
pay all Selling Expenses in connection with any sale of its Registrable
Securities hereunder.

 11
 

Section 2.08           Indemnification.

(a)           By MarkWest.  In the event of a registration of any
Registrable Securities under the Securities Act pursuant to this Agreement,
MarkWest will indemnify and hold harmless each Selling Holder thereunder, its
Affiliates that own Registrable Securities and their respective directors and
officers, and each underwriter, pursuant to the applicable underwriting
agreement with such underwriter, of Registrable Securities thereunder and each
Person, if any, who controls such Selling Holder or underwriter within the
meaning of the Securities Act and the Exchange Act (collectively, the “Selling
Holder Indemnified Persons”), against any losses, claims, damages, expenses
or liabilities (including reasonable attorneys’ fees and expenses)
(collectively, “Losses”), joint or several, to which such Selling Holder
Indemnified Person may become subject under the Securities Act, the Exchange
Act or otherwise, insofar as such Losses (or actions or proceedings, whether
commenced or threatened, in respect thereof) arise out of or are based upon any
untrue statement or alleged untrue statement of any material fact contained in
the Shelf Registration Statement or any other registration statement
contemplated by this Agreement, any preliminary prospectus or final prospectus
contained therein, or any amendment or supplement thereof, or arise out of or
are based upon the omission or alleged omission to state therein a material
fact required to be stated therein or necessary to make the statements therein
(in the case of a prospectus, in light of the circumstances under which they
were made) not misleading, and will reimburse each such Selling Holder
Indemnified Person for any legal or other expenses reasonably incurred by them
in connection with investigating or defending any such Loss or actions or
proceedings as such expenses are incurred; provided, however,
that MarkWest will not be liable in any such case if and to the extent that any
such Loss arises out of or is based upon an untrue statement or alleged untrue
statement or omission or alleged omission so made in conformity with
information furnished by such Selling Holder Indemnified Person in writing
specifically for use in the Shelf Registration Statement or such other
registration statement, or prospectus supplement, as applicable. Such indemnity
shall remain in full force and effect regardless of any investigation made by
or on behalf of such Selling Holder Indemnified Person, and shall survive the
transfer of such securities by such Selling Holder.

(b)           By Each Selling Holder.  Each Selling Holder agrees severally and not
jointly to indemnify and hold harmless MarkWest, its Affiliates and their
respective directors and officers, and each Person, if any, who controls
MarkWest within the meaning of the Securities Act or of the Exchange Act to the
same extent as the foregoing indemnity from MarkWest to the Selling Holders,
but only with respect to information regarding such Selling Holder furnished in
writing by or on behalf of such Selling Holder expressly for inclusion in the
Shelf Registration Statement or prospectus supplement relating to the
Registrable Securities, or any amendment or supplement thereto; provided,
however, that the liability of each Selling Holder shall not be greater
in amount than the dollar amount of the proceeds (net of any Selling Expenses)
received by such Selling Holder from the sale of the Registrable Securities
giving rise to such indemnification.

(c)           Notice.  Promptly after receipt by an indemnified
party hereunder of notice of the commencement of any action, such indemnified
party shall, if a claim in respect thereof is to be made against the
indemnifying party hereunder, notify the indemnifying party in writing thereof,
but the omission so to notify the indemnifying party shall not relieve it from
any liability which it may have to any indemnified party other than under this
Section 2.08.  In any action brought
against any indemnified party, it shall notify the indemnifying party of the
commencement thereof.  The indemnifying
party shall be entitled to participate in and, to the extent it shall wish, to
assume and undertake the defense thereof with counsel reasonably satisfactory
to such 

 12
 

indemnified party and,
after notice from the indemnifying party to such indemnified party of its
election so to assume and undertake the defense thereof, the indemnifying party
shall not be liable to such indemnified party under this Section 2.08 for any
legal expenses subsequently incurred by such indemnified party in connection
with the defense thereof other than reasonable costs of investigation and of
liaison with counsel so selected; provided, however, that, (i) if
the indemnifying party has failed to assume the defense and employ counsel or
(ii) if the defendants in any such action include both the indemnified party
and the indemnifying party and counsel to the indemnified party shall have
concluded that there may be reasonable defenses available to the indemnified
party that are different from or additional to those available to the
indemnifying party, or if the interests of the indemnified party reasonably may
be deemed to conflict with the interests of the indemnifying party, then the
indemnified party shall have the right to select a separate counsel and to
assume such legal defense and otherwise to participate in the defense of such
action, with the reasonable expenses and fees of such separate counsel and
other reasonable expenses related to such participation to be reimbursed by the
indemnifying party as incurred. 
Notwithstanding any other provision of this Agreement, no indemnifying
party, without the consent of the indemnified party, shall settle any action in
respect for which indemnification may be sought hereunder, unless the
settlement thereof imposes no liability or obligation on, and includes a
complete and unconditional release from all liability of, the indemnified
party.

(d)           Contribution.  If the indemnification provided for in this
Section 2.08 is held by a court or government agency of competent jurisdiction
to be unavailable to MarkWest or any Selling Holder or is insufficient to hold
them harmless in respect of any Losses, then each such indemnifying party, in
lieu of indemnifying such indemnified party, shall contribute to the amount
paid or payable by such indemnified party as a result of such Losses as between
MarkWest on the one hand and such Selling Holder on the other, in such
proportion as is appropriate to reflect the relative fault of MarkWest on the
one hand and of such Selling Holder (or other indemnified party) on the other
in connection with the statements or omissions which resulted in such Losses,
as well as any other relevant equitable considerations; provided, however,
that in no event shall such Selling Holder be required to contribute an
aggregate amount in excess of the dollar amount of proceeds (net of Selling
Expenses) received by such Selling Holder from the sale of Registrable
Securities giving rise to such indemnification. 
The relative fault of MarkWest on the one hand and each Selling Holder
on the other shall be determined by reference to, among other things, whether
the untrue or alleged untrue statement of a material fact or the omission or
alleged omission to state a material fact has been made by, or relates to,
information supplied by such party, and the parties’ relative intent,
knowledge, access to information and opportunity to correct or prevent such
statement or omission.  The parties
hereto agree that it would not be just and equitable if contributions pursuant
to this paragraph were to be determined by pro rata allocation or by any other
method of allocation which does not take account of the equitable
considerations referred to in the first sentence of this paragraph.  The amount paid by an indemnified party as a
result of the Losses referred to in the first sentence of this paragraph shall
be deemed to include any legal and other expenses reasonably incurred by such
indemnified party in connection with investigating or defending any Loss which
is the subject of this paragraph. No person guilty of fraudulent
misrepresentation (within the meaning of Section 11(f) of the Securities Act)
shall be entitled to contribution from any Person who is not guilty of such
fraudulent misrepresentation.

 13
 

(e)           Other Indemnification.  The provisions of this Section 2.08 shall be
in addition to any other rights to indemnification or contribution which an
indemnified party may have pursuant to law, equity, contract or otherwise.

Section 2.09           Rule 144 Reporting.  With a view to making available the benefits
of certain rules and regulations of the Commission that may permit the sale of
the Registrable Securities to the public without registration, MarkWest agrees
to use its commercially reasonable efforts to:

(a)           Make and keep public information
regarding MarkWest available, as those terms are understood and defined in Rule
144 under the Securities Act, at all times from and after the date hereof;

(b)           File with the Commission in a timely
manner all reports and other documents required of MarkWest under the
Securities Act and the Exchange Act at all times from and after the date
hereof; and

(c)           So long as a Holder owns any
Registrable Securities, furnish to such Holder forthwith upon request a copy of
the most recent annual or quarterly report of MarkWest, and such other reports
and documents so filed as such Holder may reasonably request in availing itself
of any rule or regulation of the Commission allowing such Holder to sell any
such securities without registration.

Section 2.10           Transfer or Assignment of
Registration Rights.  The rights to
cause MarkWest to register Registrable Securities granted to the Holders by
MarkWest under this Article II may be transferred or assigned by one or more
Holders to one or more transferee(s) or assignee(s) of such Registrable
Securities, provided that (a) unless such transferee is a Holder or an
Affiliate of the transferring Holder,
or the transfer is to a swap counterparty, following such transfer or
assignment, each such transferee or assignee owns Registrable Securities
representing at least ten million dollars ($10,000,000) of Registrable
Securities (determined by multiplying the number of Registrable Securities
owned by the average of the closing price for Common Units for the ten (10)
trading days preceding the date of such transfer or assignment) or MarkWest
otherwise consents to such transfer or assignment, (b) MarkWest is given
written notice prior to any said transfer or assignment, stating the name and
address of each such transferee and identifying the securities with respect to
which such registration rights are being transferred or assigned, and (c) each
such transferee assumes in writing responsibility for its portion of the obligations
of such Holder under this Agreement (unless it is already a party to this
Agreement).

ARTICLE III

MISCELLANEOUS

Section 3.01           Communications.  All notices and other communications provided
for or permitted hereunder shall be made in writing by facsimile, internet
electronic mail, courier service or personal delivery:

 14
 

(a)           if to the Purchasers, at the most
current addresses given by the Purchasers to MarkWest in accordance with the
provisions of this Section 3.01, which addresses initially are, with respect to
the Purchasers, the addresses set forth in the Purchase Agreement,

(b)           if to a transferee of the Purchaser,
to such Holder at the address provided pursuant to Section 2.10 above, and

(c)           if to MarkWest, at 1515 Arapahoe,
Tower 2, Suite 700, Denver, Colorado 80102, notice of which is given in
accordance with the provisions of this Section 3.01.

All such notices and
communications shall be deemed to have been received at the time delivered by
hand, if personally delivered; when receipt acknowledged, if sent via facsimile
or sent via Internet electronic mail; and when actually received, if sent by
courier service or any other means.

Section 3.02           Successor and Assigns.  This Agreement shall inure to the benefit of
and be binding upon the successors and assigns of each of the parties,
including subsequent Holders of Registrable Securities to the extent permitted
herein.

Section 3.03           Assignment of Rights.  All or any portion of the rights and
obligations of the Purchasers under this Agreement may be transferred or
assigned by the Purchasers in accordance with Section 2.10 hereof.

Section 3.04           Recapitalization, Exchanges, etc.
Affecting the Common Units.  The
provisions of this Agreement shall apply to the full extent set forth herein
with respect to any and all units of MarkWest or any successor or assign of
MarkWest (whether by merger, consolidation, sale of assets or otherwise) which
may be issued in respect of, in exchange for or in substitution of, the
Registrable Securities, and shall be appropriately adjusted for combinations,
recapitalizations and the like occurring after the date of this Agreement.

Section 3.05           Specific Performance.  Damages in the event of breach of this
Agreement by a party hereto may be difficult, if not impossible, to ascertain,
and it is therefore agreed that each such Person, in addition to and without
limiting any other remedy or right it may have, will have the right to an
injunction or other equitable relief in any court of competent jurisdiction,
enjoining any such breach, and enforcing specifically the terms and provisions
hereof, and each of the parties hereto hereby waives any and all defenses it
may have on the ground of lack of jurisdiction or competence of the court to
grant such an injunction or other equitable relief.  The existence of this right will not preclude
any such Person from pursuing any other rights and remedies at law or in equity
which such Person may have.

Section 3.06           Counterparts.  This Agreement may be executed in any number
of counterparts and by different parties hereto in separate counterparts, each
of which counterparts, when so executed and delivered, shall be deemed to be an
original and all of which counterparts, taken together, shall constitute but
one and the same Agreement.

Section 3.07           Headings.  The headings in this Agreement are for
convenience of reference only and shall not limit or otherwise affect the
meaning hereof.

 15
 

Section 3.08           Governing Law.  The laws of the State of Delaware shall
govern this Agreement without regard to principles of conflict of laws.

Section 3.09           Severability of Provisions.  Any provision of this Agreement which is
prohibited or unenforceable in any jurisdiction shall, as to such jurisdiction,
be ineffective to the extent of such prohibition or unenforceability without
invalidating the remaining provisions hereof or affecting or impairing the
validity or enforceability of such provision in any other jurisdiction.

Section 3.10           Entire Agreement.  This Agreement is intended by the parties as
a final expression of their agreement and intended to be a complete and
exclusive statement of the agreement and understanding of the parties hereto in
respect of the subject matter contained herein. 
There are no restrictions, promises, warranties or undertakings, other
than those set forth or referred to herein with respect to the rights granted
by MarkWest set forth herein.  This
Agreement supersedes all prior agreements and understandings between the
parties with respect to such subject matter.

Section 3.11           Amendment.  This Agreement may be amended only by means
of a written amendment signed by MarkWest and the Holders of a majority of the
then outstanding Registrable Securities; provided,  however, that
no such amendment shall materially and adversely affect the rights of any Holder
hereunder without the consent of such Holder.

Section 3.12           No Presumption.  In
the event any claim is made by a party relating to any conflict, omission, or
ambiguity in this Agreement, no presumption or burden of proof or persuasion
shall be implied by virtue of the fact that this Agreement was prepared by or
at the request of a particular party or its counsel.

Section 3.13           Aggregation of Registrable
Securities.  All Registrable
Securities held or acquired by any Persons who are Affiliates of one another
shall be aggregated together for the purpose of determining the availability of
any rights under this Agreement.

[The remainder of this page  is intentionally
left blank.]

 16

IN WITNESS WHEREOF, the
parties have executed this Agreement as of the date first written above.

	
  

  	
  MARKWEST ENERGY
  PARTNERS, L.P.

  	 

	
   

  	
   

  	 

	
   

  	
  By:

  	
  MarkWest Energy GP,
  L.L.C.,

  its general partner

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
  By:

  	
  /S/ NANCY K. BUESE

  	
   

  
	
   

  	
   

  	
   

  	
  Nancy K. Buese

  
	
   

  	
   

  	
   

  	
  Chief Financial Officer

  
						

 

 

	
  

  	
  ZLP FUND, L.P.

  
	
   

  	
   

  
	
   

  	
  By:

  	
  Zimmer Lucas
  Partners, LLC,

  its General Partner

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
  By:

  	
  /S/ DEVIN GEOGHEGAN

  	
   

  
	
   

  	
   

  	
  Devin Geoghegan,
  Partner

  

 

 

	
  

  	
  STRUCTURED FINANCE AMERICAS,
  LLC

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
  By:

  	
  /S/ SUNIL HARIANI

  
	
   

  	
   

  	
  Sunil Hariani

  
	
   

  	
   

  	
  V.P.

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
  By:

  	
  /S/ ANDREA LEUNG

  
	
   

  	
   

  	
  Andrea Leung

  
	
   

  	
   

  	
  V.P.

  

 

 

	
  

  	
  ROYAL BANK OF CANADA

  
	
   

  	
  by its agent

  
	
   

  	
   

  
	
   

  	
  RBC CAPITAL MARKETS CORPORATION

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
  By:

  	
  /S/ JOSEF MUSKATEL

  	
   

  
	
   

  	
   

  	
  Josef Muskatel

  
	
   

  	
   

  	
  Director and Senior
  Counsel

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
  By:

  	
  /S/ STEVEN MILKE

  	
   

  
	
   

  	
   

  	
  Steven Milke

  
	
   

  	
   

  	
  Managing Director

  
					

 

 

	
  

  	
  THE CUSHING MLP
  OPPORTUNITY FUND I, LP

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
  By:

  	
  /S/ JERRY V. SWANK

  	
   

  
	
   

  	
   

  	
  Jerry V. Swank

  
	
   

  	
   

  	
  Managing Partner

  

 

 

	
  

  	
  GPS
  INCOME FUND LP

  
	
   

  	
   

  
	
   

  	
  By:

  	
  GPS Partners, LLC,
  its General Partner

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
  By:

  	
  /S/ STEVEN SUGARMAN

  	
   

  
	
   

  	
   

  	
  Steven Sugarman,
  Partner

  

 

	
  

  	
  GPS
  HIGH YIELD EQUITIES FUND LP

  
	
   

  	
   

  
	
   

  	
  By:

  	
  GPS Partners, LLC,
  its General Partner

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
  By:

  	
  /S/ STEVEN SUGARMAN

  	
   

  
	
   

  	
   

  	
  Steven Sugarman,
  Partner

  

 

	
  

  	
  GPS
  NEW EQUITY FUND LP

  
	
   

  	
   

  
	
   

  	
  By:

  	
  GPS Partners, LLC,
  its General Partner

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
  By:

  	
  /S/ STEVEN SUGARMAN

  	
   

  
	
   

  	
   

  	
  Steven Sugarman,
  Partner

  

 

	
  

  	
  GPS
  MLP FUND LP

  
	
   

  	
   

  
	
   

  	
  By:

  	
  GPS Partners, LLC,
  its General Partner

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
  By:

  	
  /S/ STEVEN SUGARMAN

  	
   

  
	
   

  	
   

  	
  Steven Sugarman,
  Partner

  

 

	
  

  	
  AGILE
  PERFORMANCE FUND LLC

  
	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
  By:

  	
  /S/ STEVEN SUGARMAN

  	
   

  
	
   

  	
   

  	
  Steven Sugarman,
  Partner

  

 

 

	
  

  	
  KAYNE
  ANDERSON MLP INVESTMENT COMPANY

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
  By:

  	
  /S/ JAMES BAKER

  
	
   

  	
   

  	
  James Baker

  
	
   

  	
   

  	
  Vice President

  

 

 

	
  

  	
  TORTOISE
  ENERGY INFRASTRUCTURE CORPORATION

  
	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
  By:

  	
  /S/ TERRY MATLACK

  	
   

  
	
   

  	
   

  	
  Terry Matlack,
  Managing Director

  

 

	
  

  	
  TORTOISE
  ENERGY CAPITAL CORPORATION

  
	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
   

  	
   

  
	
   

  	
  By:

  	
  /S/ TERRY MATLACK

  	
   

  
	
   

  	
   

  	
  Terry Matlack,
  Managing Director

  

 

Schedule A

	
  Purchaser

  	
   

  	
  Units Purchased

  	
   

  	
  Total Purchase Price

  	
   

  
	
   

  	
   

  	
   

  	
   

  	
   

  	
   

  
	
  Kayne Anderson MLP Investment Company

  	
   

  	
  303,215

  	
   

  	
  $

  	
  10,000,030.70

  	
   

  
	
  GPS Income Fund LP

  	
   

  	
  148,239

  	
   

  	
  $

  	
  4,888,922.22

  	
   

  
	
  GPS High Yield Equities Fund LP

  	
   

  	
  36,027

  	
   

  	
  $

  	
  1,188,170.46

  	
   

  
	
  GPS New Equity Fund LP

  	
   

  	
  268,027

  	
   

  	
  $

  	
  8,839,530.46

  	
   

  
	
  GPS MLP Fund LP

  	
   

  	
  22,739

  	
   

  	
  $

  	
  749,932.22

  	
   

  
	
  Agile Performance Fund LLC

  	
   

  	
  30,321

  	
   

  	
  $

  	
  999,986.58

  	
   

  
	
  Tortoise Energy Infrastructure Corporation

  	
   

  	
  121,286

  	
   

  	
  $

  	
  4,000,012.28

  	
   

  
	
  Tortoise Energy Capital Corporation

  	
   

  	
  181,929

  	
   

  	
  $

  	
  6,000,018.42

  	
   

  
	
  Royal Bank of Canada

  	
   

  	
  1,313,933

  	
   

  	
  $

  	
  43,333,510.34

  	
   

  
	
  Structured Finance Americas, LLC

  	
   

  	
  272,893

  	
   

  	
  $

  	
  9,000,011.14

  	
   

  
	
  The Cushing MLP Opportunity Fund I, LP

  	
   

  	
  1,212,857

  	
   

  	
  $

  	
  40,000,023.86

  	
   

  
	
  ZLP Fund, L.P.

  	
   

  	
  181,929

  	
   

  	
  $

  	
  6,000,018.42

  	
   

  
	
   

  	
   

  	
   

  	
   

  	
   

  	
   

  
	
  Total

  	
   

  	
  4,093,395

  	
   

  	
  $

  	
  135,000,167.10

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00121-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00121-of-00352.parquet"}]]