<Page>

                                                           HAYNES AND BOONE, LLP
                                                                  EXECUTION COPY

                                                                   EXHIBIT 10.1.

                                CREDIT AGREEMENT

                                      among

                   MARKWEST ENERGY OPERATING COMPANY, L.L.C.,
                                as the Borrower,

                         MARKWEST ENERGY PARTNERS, L.P.,
                                 as a Guarantor

                             BANK OF AMERICA, N.A.,
                             as Administrative Agent

                                       and

                            The Lenders Party Hereto

                                   $60,000,000

                             SENIOR CREDIT FACILITY


                         BANC OF AMERICA SECURITIES LLC
                     AS SOLE LEAD ARRANGER AND BOOK MANAGER


                            DATED AS OF MAY 20, 2002

<Page>

                                TABLE OF CONTENTS

<Table>
<Caption>
                                                                                                           Page
                                                                                                           ----
<S>                                                                                                         <C>
ARTICLE I.      DEFINITIONS AND ACCOUNTING TERMS..............................................................1
      1.01        Defined Terms...............................................................................1
      1.02        Other Interpretive Provisions..............................................................23
      1.03        Accounting Terms...........................................................................23
      1.04        Rounding...................................................................................24
      1.05        References to Agreements and Laws..........................................................24

ARTICLE II.     THE COMMITMENTS AND BORROWINGS...............................................................24
      2.01        Revolver Loans.............................................................................24
      2.02        Term Loan Facility.........................................................................24
      2.03        Borrowings, Conversions and Continuations of Loans.........................................25
      2.04        Prepayments................................................................................26
      2.05        Reduction or Termination of Commitments....................................................28
      2.06        Repayment of Loans.........................................................................28
      2.07        Interest...................................................................................28
      2.08        Fees.......................................................................................29
      2.09        Computation of Interest and Fees...........................................................29
      2.10        Evidence of Debt...........................................................................29
      2.11        Payments Generally.........................................................................30
      2.12        Sharing of Payments........................................................................32
      2.13        Priority of Hedging Obligations............................................................32
      2.14        Letters of Credit..........................................................................32

ARTICLE III.    TAXES, YIELD PROTECTION AND ILLEGALITY.......................................................38
      3.01        Taxes......................................................................................38
      3.02        Illegality.................................................................................39
      3.03        Inability to Determine Rates...............................................................39
      3.04        Increased Cost and Reduced Return; Capital Adequacy; Reserves on Eurodollar Rate Loans.....40
      3.05        Funding Losses.............................................................................40
      3.06        Matters Applicable to all Requests for Compensation........................................41
      3.07        Survival...................................................................................41

ARTICLE IV.     CONDITIONS PRECEDENT TO BORROWINGS...........................................................41
      4.01        Conditions to Initial Credit Extension.....................................................41
      4.02        Deadline for Conditions Effective Date.....................................................44
      4.03        Conditions to all Loans and L/C Credit Extension...........................................44

ARTICLE V.      REPRESENTATIONS AND WARRANTIES...............................................................44
      5.01        Existence; Qualification and Power; Compliance with Laws...................................44
      5.02        Authorization; No Contravention............................................................45
      5.03        Governmental Authorization.................................................................45
      5.04        Binding Effect.............................................................................45
      5.05        Financial Statements; No Material Adverse Effect...........................................45
      5.06        Litigation.................................................................................45
      5.07        No Default.................................................................................46

                                        i
<Page>

      5.08        Ownership of Property; Liens...............................................................46
      5.09        Environmental Compliance...................................................................46
      5.10        Insurance..................................................................................46
      5.11        Taxes......................................................................................46
      5.12        ERISA Compliance...........................................................................46
      5.13        Subsidiaries and other Investments.........................................................47
      5.14        Margin Regulations; Investment Company Act; Public Utility Holding
                  Company Act; Use of Proceeds...............................................................47
      5.15        Disclosure.................................................................................47
      5.16        Labor Matters..............................................................................48
      5.17        Compliance with Laws.......................................................................48
      5.18        Third Party Approvals......................................................................48
      5.19        Solvency...................................................................................48
      5.20        Collateral.................................................................................48

ARTICLE VI.     AFFIRMATIVE COVENANTS........................................................................48
      6.01        Financial Statements.......................................................................49
      6.02        Certificates; Other Information............................................................49
      6.03        Notices....................................................................................50
      6.04        Payment of Obligations.....................................................................50
      6.05        Preservation of Existence, Etc.............................................................50
      6.06        Maintenance of Assets and Business.........................................................51
      6.07        Maintenance of Insurance...................................................................51
      6.08        Compliance with Laws and Contractual Obligations...........................................52
      6.09        Books and Records..........................................................................52
      6.10        Inspection Rights..........................................................................52
      6.11        Compliance with ERISA......................................................................52
      6.12        Use of Proceeds............................................................................52
      6.13        Material Agreements........................................................................53
      6.14        Clean Down Period..........................................................................53
      6.15        Guaranties.................................................................................53
      6.16        Further Assurances; Additional Collateral..................................................53

ARTICLE VII.    NEGATIVE COVENANTS...........................................................................54
      7.01        Liens......................................................................................54
      7.02        Investments................................................................................55
      7.03        Hedging Agreements.........................................................................56
      7.04        Indebtedness...............................................................................56
      7.05        Lease Obligations..........................................................................56
      7.06        Fundamental Changes........................................................................57
      7.07        Dispositions...............................................................................57
      7.08        Restricted Payments; Distributions and Redemptions.........................................57
      7.09        ERISA......................................................................................58
      7.10        Nature of Business; Capital Expenditures...................................................58
      7.11        Transactions with Affiliates...............................................................58
      7.12        Burdensome Agreements......................................................................58
      7.13        Use of Proceeds............................................................................58
      7.14        Material Agreements........................................................................58
      7.15        Financial Covenants........................................................................59
      7.16        Subordinated Indebtedness (Refinancing Indebtedness).......................................59

                                       ii
<Page>

ARTICLE VIII.   EVENTS OF DEFAULT AND REMEDIES................................... ...........................59
      8.01        Events of Default..........................................................................59
      8.02        Remedies Upon Event of Default.............................................................62

ARTICLE IX.     ADMINISTRATIVE AGENT.........................................................................62
      9.01        Appointment and Authorization of Administrative Agent; Lender Hedging Agreements...........63
      9.02        Delegation of Duties.......................................................................63
      9.03        Default; Collateral; Agreement Regarding Collateral........................................63
      9.04        Liability of Administrative Agent..........................................................65
      9.05        Reliance by Administrative Agent...........................................................65
      9.06        Notice of Default..........................................................................66
      9.07        Credit Decision; Disclosure of Information by Administrative Agent.........................66
      9.08        Indemnification of Administrative Agent....................................................66
      9.09        Administrative Agent in its Individual Capacity............................................67
      9.10        Successor Administrative Agent.............................................................67
      9.11        Other Agents; Lead Managers................................................................67

ARTICLE X.      MISCELLANEOUS................................................................................68
      10.01       Amendments, Release of Collateral, Etc.....................................................68
      10.02       Notices and Other Communications; Facsimile Copies.........................................70
      10.03       No Waiver; Cumulative Remedies.............................................................70
      10.04       Attorney Costs; Expenses and Taxes.........................................................71
      10.05       Indemnification............................................................................71
      10.06       Payments Set Aside.........................................................................72
      10.07       Successors and Assigns.....................................................................72
      10.08       Confidentiality............................................................................75
      10.09       Set-off....................................................................................75
      10.10       Interest Rate Limitation...................................................................75
      10.11       Counterparts...............................................................................76
      10.12       Integration................................................................................76
      10.13       Survival of Representations and Warranties.................................................76
      10.14       Severability...............................................................................76
      10.15       Foreign Lenders............................................................................76
      10.16       Governing Law..............................................................................77
      10.17       Waiver of Right to Trial by Jury, Etc......................................................78
      10.18       Agreement Regarding Collateral.............................................................78
      10.19       No General Partner's Liability.............................................................78
      10.20       ENTIRE AGREEMENT...........................................................................78

      SIGNATURES............................................................................................S-1

SCHEDULES

      2.01      Commitments
      5.13      Subsidiaries and other Equity Investments
      7.01      Existing Liens
      7.12      Agreements Restricting Liens on Leasehold Interests
      10.02     Addresses for Notices to Borrower, Guarantors and Administrative Agent
</Table>

                                       iii
<Page>

EXHIBITS

<Table>
<Caption>
     Exhibit:   Form Of:
     --------   --------
     <S>        <C>
     A-1        Borrowing Notice
     A-2        Conversion/Continuation Notice
     B-1        Revolver Note
     B-2        Term Note
     C          Compliance Certificate pursuant to SECTION 6.02(a)
     D          Assignment and Assumption
     E-1        Subsidiary Guaranty
     E-2        Guaranty (MLP)
     E-3        Limited Guaranty (MarkWest Parent)
     F-1        Legal Opinion of Davis, Graham & Stubbs LLP
     F-2        Legal Opinion of Barry Spector
     F-3        Legal Opinion of Baker Botts LLP
     G-1        Borrower Pledge and Security Agreement
     G-2        Subsidiary Pledge and Security Agreement
     G-3        MLP Pledge and Security Agreement
     H          Agreement Regarding Collateral
</Table>

                                       iv
<Page>

                                CREDIT AGREEMENT

     This CREDIT AGREEMENT ("AGREEMENT") is entered into as of May 20, 2002,
among MARKWEST ENERGY OPERATING COMPANY, L.L.C., a Delaware limited liability
company (the "BORROWER"), MARKWEST ENERGY PARTNERS, L.P., a Delaware limited
partnership (the "MLP"), each lender from time to time party hereto
(collectively, the "LENDERS" and individually, a "LENDER"), and BANK OF AMERICA,
N.A., as Administrative Agent.

     The Borrower has requested that the Lenders provide a secured term loan
facility and a secured revolving credit facility, and the Lenders are willing to
do so on the terms and conditions set forth herein.

     In consideration of the mutual covenants and agreements herein contained,
the parties hereto covenant and agree as follows:

                                   ARTICLE I.
                        DEFINITIONS AND ACCOUNTING TERMS

     1.01  DEFINED TERMS.

     As used in this Agreement, the following terms shall have the meanings set
forth below:

     ACQUISITION means any transaction or series of related transactions for the
purpose of, or resulting in, directly or indirectly, (a) the acquisition by a
Company of all or substantially all of the assets located in the United States
or Canada of a Person or of any business or division of a Person; (b) the
acquisition by a Company of more than 50% of any class of Voting Stock (or
similar ownership interests) of any Domestic Person; or (c) a merger,
consolidation, amalgamation, or other combination by a Company with another
Person if a Company is the surviving entity, PROVIDED THAT, (i) in any merger
involving the Borrower, the Borrower must be the surviving entity; and (ii) in
any merger involving a Wholly-Owned Subsidiary and another Subsidiary, a
Wholly-Owned Subsidiary shall be the survivor.

     ACQUISITION SUBFACILITY has the meaning specified in SECTION 2.01(b).

     ACQUISITION SUBFACILITY COMMITMENT means an amount (subject to reduction or
cancellation as herein provided) equal to $28,600,000.

     ADMINISTRATIVE AGENT means Bank of America in its capacity as
administrative agent under any of the Loan Documents, or any successor
administrative agent.

     ADMINISTRATIVE AGENT'S OFFICE means the Administrative Agent's address and,
as appropriate, account as set forth on SCHEDULE 10.02, or such other address or
account as the Administrative Agent may from time to time notify to the Borrower
and the Lenders.

     ADMINISTRATIVE DETAILS FORM means the Administrative Details Reply Form
furnished by a Lender to the Administrative Agent in connection with this
Agreement.

     AFFILIATE means, as to any Person, any other Person directly or indirectly
controlling, controlled by, or under direct or indirect common control with,
such Person. A Person shall be deemed to be controlled by any other Person if
such other Person possesses, directly or indirectly, power (a) to vote 10% or
more of the securities (on a fully diluted basis) having ordinary voting power
for the election of

                                        1
<Page>

directors, managing members, or managing general partners; or (b) to direct or
cause the direction of the management and policies of such Person whether by
contract or otherwise.

     AGENT/ARRANGER FEE LETTER has the meaning specified in SECTION 2.08(b).

     AGENT-RELATED PERSONS means the Administrative Agent (including any
successor administrative agent), together with its Affiliates (including, in the
case of Bank of America in its capacity as the Administrative Agent, Banc of
America Securities LLC), and the officers, directors, employees, agents and
attorneys-in-fact of such Persons and Affiliates.

     AGGREGATE COMMITMENTS has the meaning set forth in the definition of
"COMMITMENT."

     AGGREGATE COMMITTED SUM means, on any date of determination, the sum of all
Committed Sums then in effect for all Lenders in respect of the Revolver
Facility and the Term Loan Facility (as the same may have been reduced or
canceled as provided in the Loan Documents).

     AGREEMENT means this Credit Agreement.

     AGREEMENT REGARDING COLLATERAL means that certain Agreement Regarding
Collateral dated as of even date herewith, by and among the MLP, the Borrower,
MarkWest Parent, the Administrative Agent, and Bank of America, N.A., as agent
under the Parent Credit Agreement substantially in the form of EXHIBIT H hereto.

     APPLICABLE RATE means the following percentages per annum set forth in the
table below, on any date of determination, with respect to the Type of Credit
Extension or commitment fee that corresponds to the Leverage Ratio at such date
of determination, as calculated based on the quarterly Compliance Certificate
most recently delivered pursuant to SECTION 6.02(a):

<Table>
<Caption>
        --------------------------------------------------------------------------------
                                         APPLICABLE RATE
        --------------------------------------------------------------------------------
                                                                       Letter of
         Pricing          Leverage Ratio         Commitment   Credit and     Base Rate +
          Level                                   fee (bps)   Eurodollar        (bps)
                                                             Rate + (bps)
        --------------------------------------------------------------------------------
           <S>       <C>                              <C>         <C>           <C>
           1           Less than or equal to          25.0        175.0          37.5
                             1.00:1.00
        --------------------------------------------------------------------------------
           2           Greater than 1.00:1.00         30.0        200.0          62.5
                     but less than or equal to
                             2.00:1.00
        --------------------------------------------------------------------------------
           3           Greater than 2.00:1.00         37.5        225.0          87.5
                     but less than or equal to
                             2.50:1.00
        --------------------------------------------------------------------------------
           4           Greater than 2.50:1.00         50.0        250.0         112.5
                     but less than or equal to
                            2.75:1.00
        --------------------------------------------------------------------------------
           5           Greater than 2.75:1.00         50.0        275.0         137.5
        --------------------------------------------------------------------------------
</Table>

     Any increase or decrease in the Applicable Rate resulting from a change in
the Leverage Ratio shall become effective as of the first day of the fiscal
quarter of the Borrower immediately following the date of a Compliance
Certificate delivered pursuant to SECTION 6.02; provided, however, that if no
Compliance Certificate is delivered during a fiscal quarter when due in
accordance with such Section, the

                                        2
<Page>

Pricing Level 4 shall apply as of the first day of such following fiscal
quarter. The Applicable Rate in effect from the Closing Date through September
30, 2002, shall be determined based upon Pricing Level 3, UNLESS the
Overallotment is purchased, in which case the Applicable Rate in effect from the
Closing Date through September 30, 2002, shall be determined based upon Pricing
Level 2. The Applicable Rate in effect beginning October 1, 2002 shall be based
upon the Leverage Ratio certified in the Compliance Certificate delivered for
the fiscal quarter ending June 30, 2002.

     APPROVED FUND means any Fund that is administered or managed by a Lender,
an Affiliate of a Lender, or an entity or an Affiliate of an entity that
administers or manages a Lender.

     ARRANGER means Banc of America Securities LLC, in its capacity as sole lead
arranger and book manager.

     ASSIGNMENT AND ASSUMPTION means an Assignment and Assumption substantially
in the form of EXHIBIT D.

     ATTORNEY COSTS means and includes the fees and disbursements of any law
firm or other external counsel and the allocated cost of internal legal services
and all disbursements of internal counsel.

     ATTRIBUTABLE INDEBTEDNESS means, on any date, (a) in respect of any Capital
Lease of any Person, the capitalized amount thereof that would appear on a
balance sheet of such Person prepared as of such date in accordance with GAAP,
and (b) in respect of any Synthetic Lease Obligation, the capitalized amount of
the remaining lease payments under the relevant lease that would appear on a
balance sheet of such Person prepared as of such date in accordance with GAAP if
such lease were accounted for as a capital lease.

     AUTHORIZATIONS means all filings, recordings, and registrations with, and
all validations or exemptions, approvals, orders, authorizations, consents,
franchises, licenses, certificates, and permits from, any Governmental
Authority.

     BANK GUARANTIES means guaranties or other agreements or instruments serving
a similar function issued by a bank or other financial institution.

     BANK OF AMERICA means Bank of America, N.A.

     BASE RATE means for any day a fluctuating rate per annum equal to the
higher of (a) the Federal Funds Rate plus 1/2 of 1% and (b) the rate of interest
in effect for such day as publicly announced from time to time by Bank of
America as its "PRIME RATE." Such rate is a rate set by Bank of America based
upon various factors including Bank of America's costs and desired return,
general economic conditions and other factors, and is used as a reference point
for pricing some loans, which may be priced at, above, or below such announced
rate. Any change in such rate announced by Bank of America shall take effect at
the opening of business on the day specified in the public announcement of such
change.

     BASE RATE LOAN means a Loan that bears interest based on the Base Rate.

     BOARD means the Board of Governors of the Federal Reserve System of the
United States of America.

     BORROWER has the meaning set forth in the introductory paragraph hereto.

                                        3
<Page>

     BORROWER AFFILIATE means the Borrower, the General Partner, the MLP, and
each of their respective Subsidiaries.

     BORROWER OPERATING AGREEMENTS means the Organization Documents of each of
the General Partner, the MLP, the Borrower and each of their respective
Subsidiaries.

     BORROWING means a borrowing consisting of simultaneous Loans of the same
Type and having the same Interest Period made by each of the Lenders pursuant to
SECTION 2.01 or 2.02.

     BORROWING NOTICE means a notice of (a) a Borrowing, (b) a conversion of
Loans from one Type to the other, or (c) a continuation of Loans as the same
Type, pursuant to SECTION 2.03(a), which, if in writing, shall be substantially
in the form of EXHIBIT A-1 or A-2, as applicable.

     BUSINESS DAY means any day other than a Saturday, Sunday, or other day on
which commercial banks are authorized to close under the Laws of, or are in fact
closed in, the state where the Administrative Agent's Office is located and, if
such day relates to any Eurodollar Rate Loan, means any such day on which
dealings in Dollar deposits are conducted by and between banks in the applicable
offshore Dollar interbank market.

     CANADIAN CREDIT AGREEMENT means the Amended and Restated Credit Agreement
among MarkWest Resources Canada Corp., Bank of America, N.A., acting through its
Canadian branch, as Canadian administrative agent, and the lenders parties
thereto, dated as of the Conditions Effective Date, as may be amended from time
to time.

     CAPITAL EXPENDITURE by a Person means an expenditure (determined in
accordance with GAAP) for any fixed asset owned by such Person for use in the
operations of such Person having a useful life of more than one year, or any
improvements or additions thereto.

     CAPITAL LEASE means any capital lease or sublease which should be
capitalized on a balance sheet in accordance with GAAP.

     CASH COLLATERALIZE means to pledge and deposit with or deliver to the
Administrative Agent, for the benefit of the L/C Issuer and the Lenders, as
collateral for the L/C Obligations, cash and deposit account balances pursuant
to documentation in form and substance satisfactory to the Administrative Agent
and the L/C Issuer (which documents hereby are consented to by the Lenders).

     CASH EQUIVALENTS means:

           (a) United States Dollars;

           (b) direct general obligations, or obligations of, or obligations
     fully and unconditionally guaranteed as to the timely payment of principal
     and interest by, the United States or any agency or instrumentality thereof
     having remaining maturities of not more than thirteen (13) months, but
     excluding any such securities whose terms do not provide for payment of a
     fixed dollar amount upon maturity or call for redemptions;

           (c) certificates of deposit and eurodollar time deposits with
     maturities of thirteen (13) months or less, bankers acceptances with
     maturities not exceeding one hundred eighty (180) days, overnight bank
     deposits and other similar short term instruments, in each case with any

                                        4
<Page>

     domestic commercial bank having capital and surplus in excess of
     $250,000,000 and having a rating of at least "A2" by Moody's and at least
     "A" by S&P;

           (d) repurchase obligations with a term of not more than thirteen (13)
     months for underlying securities of the types described in (b) and (c)
     above entered into with any financial institution meeting the
     qualifications in (c) above;

           (e) commercial paper (having original maturities of not more than two
     hundred seventy (270) days) of any Person rated "P-1" or better by Moody's
     or "A-1" or the equivalent by S&P; and

           (f) money market mutual or similar funds having assets in excess of
     $100,000,000, at least 95% of the assets of which are comprised of assets
     specified in clause (a) through (e) above.

     CHANGE OF CONTROL means (a) MarkWest Parent shall fail to own, directly or
indirectly, at least 51% of the general partnership interests and at least 33
1/3% of the limited partnership interests in the MLP, (b) any Person, entity or
group (other than MarkWest Parent) acquires beneficial ownership (within the
meaning of Rule 13d-3 of the Securities and Exchange Commission under the
Securities Exchange Act of 1934) of 33 1/3% or more of the equity interests in
the MLP, (c) any two Persons, entities or groups (other than MarkWest Parent)
acquires beneficial ownership (within the meaning of Rule 13d-3 of the
Securities and Exchange Commission under the Securities Exchange Act of 1934) of
51% or more of the equity interests in the MLP, (d) the MLP shall fail to own,
directly or indirectly, 100% of the equity interests in the Borrower, (e)
MarkWest Parent fails for any reason to control the management of the MLP or
fails to control the management of the Borrower, or (f) a Parent Change of
Control shall occur.

     CHANGE IN LAW means (a) the adoption of any law, rule or regulation after
the date of this Agreement, (b) any change in any law, rule or regulation or in
the interpretation or application thereof by any Governmental Authority after
the date of this Agreement or (c) compliance by any Lender or the Issuing Bank
(or, for purposes of SECTION 3.04(b), by any lending office of such Lender or by
such Lender's or the Issuing Bank's holding company, if any) with any request,
guideline or directive (whether or not having the force of law) of any
Governmental Authority made or issued after the date of this Agreement.

     CLEAN DOWN PERIOD has the meaning set forth in SECTION 6.14.

     CLOSING DATE means the date upon which this Agreement has been executed by
the Borrower, the MLP, the Lenders and the Administrative Agent.

     CODE means the Internal Revenue Code of 1986.

     COLLATERAL means all property and interests in property and proceeds
thereof now owned or hereafter acquired by the MLP, the Borrower, and their
respective Subsidiaries in or upon which a Lien now or hereafter exists in favor
of the Lenders, or the Administrative Agent on behalf of the Lenders, including,
but not limited to substantially all of the assets (including stock and other
equity interests) of the MLP, the Borrower, and their respective Subsidiaries,
whether under this Agreement, the Collateral Documents, or under any other
document executed by any Borrower Affiliate and delivered to the Administrative
Agent or the Lenders.

                                        5
<Page>

     COLLATERAL DOCUMENTS means (a) each guaranty, pledge agreement, security
agreement, mortgage, assignment, and all other security agreements, deeds of
trust, mortgages, chattel mortgages, assignments, pledges, guaranties, financing
statements, continuation statements, extension agreements and other similar
agreements or instruments executed by the Borrower, the MLP, any Guarantor, or
any of their respective Subsidiaries for the benefit of the Lenders now or
hereafter delivered to the Lenders or the Administrative Agent pursuant to or in
connection with the transactions contemplated hereby, and all financing
statements (or comparable documents now or hereafter filed in accordance with
the Uniform Commercial Code or comparable law) against the Borrower, the MLP,
any Guarantor, or any of their respective Subsidiaries as debtor in favor of the
Lenders or the Administrative Agent for the benefit of the Lenders as secured
party to secure or guarantee the payment of any part of the Obligations or the
performance of any other duties and obligations of Borrower under the Loan
Documents, whenever made or delivered, and (b) any amendments, supplements,
modifications, renewals, replacements, consolidations, substitutions,
restatements, and extensions of any of the foregoing.

     COMMITMENT means, as to each Lender, its obligation to make (i) Loans to
the Borrower pursuant to SECTION 2.01, in an amount at any one time outstanding
not to exceed its Committed Sum, (ii) make Loans to the Borrower on the
Conditions Effective Date pursuant to SECTION 2.02, in an amount not to exceed
its Committed Sum, and (iii) to purchase participations in L/C Obligations
pursuant to SECTION 2.14, in an aggregate principal amount at any one time
outstanding not to exceed, when aggregated with the Loans made pursuant to
SECTION 2.01, its Committed Sum, in each case as such amount may be reduced or
adjusted from time to time in accordance with this Agreement (collectively, the
"AGGREGATE COMMITMENTS"), in each case as such amount may be reduced or adjusted
from time to time in accordance with this Agreement (collectively, the
"AGGREGATE COMMITMENTS").

     COMMITTED SUM means for any Lender (a) with respect to the Acquisition
Subfacility, at any date of determination occurring prior to the Maturity Date,
the amount stated beside such Lender's name under the heading for the
Acquisition Subfacility on the most-recently amended SCHEDULE 2.01 to this
Agreement (which amount is subject to increase, reduction, or cancellation in
accordance with the Loan Documents), (b) with respect to the Working
Capital/Distribution Subfacility, at any date of determination occurring prior
to the Maturity Date, the amount stated beside such Lender's name under the
heading for the Working Capital/Distribution Subfacility on the most recently
amended SCHEDULE 2.01 to this Agreement (which amount is subject to increase,
reduction, or cancellation in accordance with the Loan Documents), and (c) with
respect to the Term Loan Facility, at any date of determination occurring prior
to the Maturity Date, the amount stated beside such Lender's name under the
heading for the Term Loan Facility on the most-recently amended SCHEDULE 2.01 to
this Agreement (which amount is subject to increase, reduction, or cancellation
in accordance with the Loan Documents).

     COMPANY and COMPANIES means, on any date of determination thereof, the MLP,
the Borrower and each of their respective Subsidiaries.

     COMPENSATION PERIOD has the meaning set forth in SECTION 2.11(e)(ii).

     COMPLIANCE CERTIFICATE means a certificate substantially in the form of
EXHIBIT C.

     CONDITIONS EFFECTIVE DATE means the first date all the conditions precedent
in SECTION 4.01 are satisfied or waived in accordance with SECTION 4.01 (or, in
the case of SECTIONS 4.01(b) and (c), waived by the Person entitled to receive
the applicable payment).

     CONSOLIDATED EBITDA means, for any period, for the MLP and its Subsidiaries
on a consolidated basis, an amount equal to the sum of (a) Consolidated Net
Income, (b) Consolidated Interest Charges, (c)

                                        6
<Page>

the amount of taxes, based on or measured by income, used or included in the
determination of such Consolidated Net Income, (d) the amount of depreciation,
depletion, and amortization expense deducted in determining such Consolidated
Net Income, and (e) other non-cash charges and expenses, including, without
limitation, non-cash charges and expenses relating to Swap Contracts or
resulting from accounting convention changes, of the MLP and its Subsidiaries on
a consolidated basis, all determined in accordance with GAAP.

     For purposes of calculating compliance with SECTION 7.15, (A) Consolidated
EBITDA for any fiscal quarter ending on or prior to March 31, 2002 shall be the
pro forma results of the MLP set forth in financial statements provided by the
Borrower to the Administrative Agent and to each Lender, which financial
information shall be prepared using a methodology substantially similar to the
methodology used in preparing the pro forma results of the MLP as set forth in
the MLP Registration Statement, and (B) Consolidated EBITDA for any fiscal
quarter ending on or after June 30, 2002 shall be the actual results of the MLP
as set forth in financial statements filed with the Securities and Exchange
Commission in the Form 10-Q for the quarter ended June 30, 2002, adjusted on a
pro forma basis as necessary for the period prior to the MLP Offering Closing,
in each case with respect to which financial statements the Borrower shall have
provided a certificate containing the representations and warranties set forth
in SECTION 5.05(a).

     CONSOLIDATED FUNDED DEBT means, as of any date of determination, for the
MLP and its Subsidiaries on a consolidated basis, the sum of (a) the outstanding
principal amount of all obligations and liabilities, whether current or
long-term, for borrowed money (including Obligations hereunder), (b) Capital
Leases, (c) Synthetic Lease Obligations, and (d) without duplication, all
Guaranty Obligations with respect to Indebtedness of the type specified in
subsections (a) through (c) above.

     CONSOLIDATED INTEREST CHARGES means, for any period, for the MLP and its
Subsidiaries on a consolidated basis, the sum of (a) all interest, premium
payments, fees, charges and related expenses of the MLP and its Subsidiaries in
connection with Indebtedness (including capitalized interest), in each case to
the extent treated as interest in accordance with GAAP, and (b) the portion of
rent expense of the MLP and its Subsidiaries with respect to such period under
Capital Leases that is treated as interest in accordance with GAAP.

     CONSOLIDATED NET INCOME means, for any period, for the MLP and its
Subsidiaries on a consolidated basis, the net income or net loss of the MLP and
its Subsidiaries from continuing operations, provided that there shall be
excluded from such net income (to the extent otherwise included therein): (a)
the income (or loss) of any entity other than a Subsidiary in which the MLP or
any Subsidiary has an ownership interest, except to the extent that any such
income has been actually received by the MLP or such Subsidiary in the form of
cash dividends or similar cash distributions; (b) net extraordinary gains and
losses (other than, in the case of losses, losses resulting from charges against
net income to establish or increase reserves for potential environmental
liabilities and reserves for exposure under rate cases), (c) any gains or losses
attributable to non-cash write-ups or write-downs of assets, (d) proceeds of any
insurance on property, plant or equipment other than business interruption
insurance, (e) any gain or loss, net of taxes, on the sale, retirement or other
disposition of assets (including the capital stock or other equity ownership of
any other person, but excluding the sale of inventories in the ordinary course
of business), and (f) the cumulative effect of a change in accounting
principles.

     CONTRACTUAL OBLIGATION means, as to any Person, any provision of any
security issued by such Person or of any agreement, instrument or other
undertaking to which such Person is a party or by which it or any of its
property is bound.

                                        7
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     CONTRIBUTION AGREEMENT means the Contribution, Conveyance and Assumption
Agreement dated as of the date of MLP Offering Closing among the MLP, the
Borrower, MarkWest Parent, and certain Affiliates of MarkWest Parent.

     CREDIT EXTENSION means each of the following: (a) a Borrowing and (b) an
L/C Credit Extension.

     DEBTOR RELIEF LAWS means the Bankruptcy Code of the United States of
America, and all other liquidation, conservatorship, bankruptcy, assignment for
the benefit of creditors, moratorium, rearrangement, receivership, insolvency,
reorganization, or similar debtor relief Laws of the United States of America or
other applicable jurisdictions from time to time in effect and affecting the
rights of creditors generally.

     DEFAULT means any event that, with the giving of any notice, the passage of
time, or both, would be an Event of Default.

     DEFAULT RATE means an interest rate equal to (a) the Base Rate PLUS (b) the
Applicable Rate, if any, applicable to Base Rate Loans PLUS (c) 2% per annum;
PROVIDED, HOWEVER, that with respect to a Eurodollar Rate Loan, the Default Rate
shall be an interest rate equal to the interest rate (including any Applicable
Rate) otherwise applicable to such Loan plus 2% per annum, in each case to the
fullest extent permitted by applicable Laws.

     DISPOSITION or DISPOSE means the sale, transfer, license or other
disposition (including any sale and leaseback transaction) of any property
(including stock, partnership and other equity interests) by any Person of
property owned by such Person, including any sale, assignment, transfer or other
disposal, with or without recourse, of any notes or accounts receivable or any
rights and claims associated therewith.

     DISTRIBUTION LOAN means a Loan which is made in whole or in part for the
purpose of paying a Quarterly Distribution or for the purpose of reimbursing the
General Partner for the purchase price of partnership units purchased under the
MLP's long-term incentive plan.

     DOLLAR and $ means lawful money of the United States of America.

     DOMESTIC PERSON means any corporation, general partnership, limited
partnership, or limited liability company that is organized under the laws of
the United States of America or any state thereof or the District of Columbia.

     ELIGIBLE ASSIGNEE means (a) a Lender; (b) an Affiliate of a Lender; (c) an
Approved Fund and (d) any other Person (other than a natural Person) approved by
the Administrative Agent and, unless an Event of Default has occurred and is
continuing, the Borrower (each such approval not to be unreasonably withheld or
delayed); PROVIDED that notwithstanding the foregoing, "Eligible Assignee" shall
not include the Borrower, the MLP, any MarkWest Party, or any of their
respective Affiliates or Subsidiaries.

     ENVIRONMENTAL LAW means any applicable Law that relates to (a) the
condition or protection of air, groundwater, surface water, soil, or other
environmental media, (b) the environment, including natural resources or any
activity which affects the environment, (c) the regulation of any pollutants,
contaminants, wastes, substances, and Hazardous Substances, including, without
limitation, the Comprehensive Environmental Response, Compensation, and
Liability Act (42 U.S.C. Section 9601 et seq.) ("CERCLA"), the Clean Air Act (42
U.S.C. Section 7401 et seq.), the Federal Water Pollution Control Act, as
amended by the Clean Water Act (33 U.S.C. Section 1251 et seq.), the Federal
Insecticide, Fungicide, and Rodenticide Act (7 U.S.C. Section 136 et seq.), the
Emergency Planning and Community Right to Know Act of

                                        8
<Page>

1986 (42 U.S.C. Section 11001 et seq.), the Hazardous Materials Transportation
Act (49 U.S.C. Section 1801 et seq.), the National Environmental Policy Act of
1969 (42 U.S.C. Section 4321 et seq.), the Oil Pollution Act (33 U.S.C. Section
2701 et seq.), the Resource Conservation and Recovery Act (42 U.S.C. Section
6901 et seq.), the Rivers and Harbors Act (33 U.S.C. Section 401 et seq.), the
Safe Drinking Water Act (42 U.S.C. Section 201 and Section 300f et seq.), the
Solid Waste Disposal Act, as amended by the Resource Conservation and Recovery
Act of 1976 and the Hazardous and Solid Waste Amendments of 1984 (42 U.S.C.
Section 6901 et seq.), the Toxic Substances Control Act (15 U.S.C. Section 2601
et seq.), and analogous state and local Laws, as any of the foregoing may have
been and may be amended or supplemented from time to time, and any analogous
enacted or adopted Law, or (d) the Release or threatened Release of Hazardous
Substances.

     EQUITABLE LEASES means the Lease Agreement executed by Equitable Production
Company as lessor and MarkWest Energy Appalachia, L.L.C. as lessee, and the
Equipment Lease Agreement and Pipeline Lease Agreement for Maytown to Institute
Pipeline dated May 28, 1999, executed by Equitable Production Company as lessor
and MarkWest Energy Appalachia, L.L.C. as lessee.

     ERISA means the Employee Retirement Income Security Act of 1974 and any
regulations issued pursuant thereto.

     ERISA AFFILIATE means any trade or business (whether or not incorporated)
under common control with the Borrower within the meaning of SECTION 414(b) or
(c) of the Code (and SECTIONS 414(m) and (o) of the Code for purposes of
provisions of this Agreement relating to obligations imposed under SECTION 412
of the Code).

     ERISA EVENT means (a) a Reportable Event with respect to a Pension Plan;
(b) a withdrawal by the Borrower or any ERISA Affiliate from a Pension Plan
subject to SECTION 4063 of ERISA during a plan year in which it was a
substantial employer (as defined in SECTION 4001(a)(2) of ERISA) or a cessation
of operations that is treated as such a withdrawal under SECTION 4062(e) of
ERISA; (c) a complete or partial withdrawal by the Borrower or any ERISA
Affiliate from a Multiemployer Plan or notification that a Multiemployer Plan is
in reorganization; (d) the filing of a notice of intent to terminate, the
treatment of a Plan amendment as a termination under SECTIONS 4041 or 4041A of
ERISA, or the commencement of proceedings by the PBGC to terminate a Pension
Plan or Multiemployer Plan; (e) an event or condition which might reasonably be
expected to constitute grounds under SECTION 4042 of ERISA for the termination
of, or the appointment of a trustee to administer, any Pension Plan or
Multiemployer Plan; or (f) the imposition of any liability under TITLE IV of
ERISA, other than PBGC premiums due but not delinquent under SECTION 4007 of
ERISA, upon the Borrower or any ERISA Affiliate.

     EURODOLLAR RATE means for any Interest Period with respect to any
Eurodollar Rate Loan:

           (a) the rate per annum equal to the rate determined by the
     Administrative Agent to be the offered rate that appears on the page (such
     page currently being page 3750) of the Telerate screen (or any successor
     thereto) that displays an average British Bankers Association Interest
     Settlement Rate for deposits in Dollars (for delivery on the first day of
     such Interest Period) with a term equivalent to such Interest Period,
     determined as of approximately 11:00 a.m. (London time) two Business Days
     prior to the first day of such Interest Period, or

           (b) if the rate referenced in the preceding subsection (a) does not
     appear on such page or service or such page or service shall cease to be
     available, the rate per annum equal to the rate determined by the
     Administrative Agent to be the offered rate on such other page or other
     service that displays an average British Bankers Association Interest
     Settlement Rate for deposits in Dollars (for delivery on the first day of
     such Interest Period) with a term equivalent to such

                                        9
<Page>

     Interest Period, determined as of approximately 11:00 a.m. (London time)
     two Business Days prior to the first day of such Interest Period, or

           (c) if the rates referenced in the preceding subsections (a) and (b)
     are not available, the rate per annum determined by the Administrative
     Agent as the rate of interest (rounded upward to the next 1/100th of 1%) at
     which deposits in Dollars for delivery on the first day of such Interest
     Period in same day funds in the approximate amount of the Eurodollar Rate
     Loan being made, continued or converted by Bank of America and with a term
     equivalent to such Interest Period would be offered by Bank of America's
     London Branch to major banks in the offshore Dollar market at their request
     at approximately 11:00 a.m. (London time) two Business Days prior to the
     first day of such Interest Period.

     EURODOLLAR RATE LOAN means a Loan that bears interest at a rate based on
the Eurodollar Rate.

     EVENT OF DEFAULT means any of the events or circumstances specified in
ARTICLE VIII.

     EVERGREEN LETTER OF CREDIT has the meaning specified in SECTION
2.14(b)(iii).

     FEDERAL FUNDS RATE means, for any day, the rate per annum (rounded upwards
to the nearest 1/100 of 1%) equal to the weighted average of the rates on
overnight Federal funds transactions with members of the Federal Reserve System
arranged by Federal funds brokers on such day, as published by the Federal
Reserve Bank on the Business Day next succeeding such day; PROVIDED that (a) if
such day is not a Business Day, the Federal Funds Rate for such day shall be
such rate on such transactions on the next preceding Business Day as so
published on the next succeeding Business Day, and (b) if no such rate is so
published on such next succeeding Business Day, the Federal Funds Rate for such
day shall be the average rate charged to Bank of America on such day on such
transactions as determined by the Administrative Agent.

     FOREIGN LENDER has the meaning specified in SECTION 10.15.

     FRACTIONATION, STORAGE AND LOADING AGREEMENT (SILOAM) means the
Fractionation, Storage and Loading Agreement (Siloam) agreement between MarkWest
Energy Appalachia, L.L.C. and MarkWest Parent dated as of the Conditions
Effective Date.

     FUND means any Person (other than a natural person) that is (or will be)
engaged in making, purchasing, holding or otherwise investing in commercial
loans and similar extensions of credit in the ordinary course of its business.

     GAAP means generally accepted accounting principles set forth in the
opinions and pronouncements of the Accounting Principles Board and the American
Institute of Certified Public Accountants and statements and pronouncements of
the Financial Accounting Standards Board or such other principles as may be
approved by a significant segment of the accounting profession, that are
applicable to the circumstances as of the date of determination, consistently
applied. If at any time any change in GAAP would affect the computation of any
financial ratio or requirement set forth in any Loan Document, and either the
Borrower or the Required Lenders shall so request, the Administrative Agent, the
Lenders and the Borrower shall negotiate in good faith to amend such ratio or
requirement to preserve the original intent thereof in light of such change in
GAAP (subject to the approval of the Required Lenders); PROVIDED THAT, until so
amended, (a) such ratio or requirement shall continue to be computed in
accordance with GAAP prior to such change therein and (b) the Borrower shall
provide to the Administrative Agent and the Lenders financial statements and
other documents required under this

                                       10
<Page>

Agreement or as reasonably requested hereunder setting forth a reconciliation
between calculations of such ratio or requirement made before and after giving
effect to such change in GAAP.

     GAS PROCESSING AGREEMENT (KENOVA, BOLDMAN AND COBB PLANTS) means the Gas
Processing Agreement (Kenova, Boldman and Cobb Plants) between MarkWest Energy
Appalachia, L.L.C. and MarkWest Parent dated as of the Conditions Effective
Date.

     GENERAL PARTNER means MarkWest Energy GP, L.L.C., the general partner of
the MLP.

     GOVERNMENTAL AUTHORITY means any nation or government, any state or other
political subdivision thereof, any agency, authority, instrumentality,
regulatory body, court, administrative tribunal, central bank or other legal
entity exercising executive, legislative, judicial, taxing, regulatory or
administrative powers or functions of or pertaining to government.

     GUARANTORS means any Person, including the MLP and every present and future
Subsidiary of Borrower and the MLP, which undertakes to be liable for all or any
part of the Obligations by execution of a Guaranty, or otherwise.

     GUARANTY means a Guaranty now or hereafter made by any Guarantor in favor
of the Administrative Agent on behalf of the Lenders, substantially in the form
of EXHIBIT E-1, EXHIBIT E-2, or EXHIBIT E-3, as may be amended from time to
time.

     GUARANTY OBLIGATION means, as to any Person, (a) any obligation, contingent
or otherwise, of such Person guaranteeing or having the economic effect of
guaranteeing any Indebtedness or other payment obligation of another Person (the
"PRIMARY OBLIGOR") in any manner, whether directly or indirectly, and including
any obligation of such Person, direct or indirect, (i) to purchase or pay (or
advance or supply funds for the purchase or payment of) such Indebtedness or
other payment obligation, (ii) to purchase or lease property, securities or
services for the purpose of assuring the obligee in respect of such Indebtedness
or other payment obligation of the payment of such Indebtedness or other payment
obligation, (iii) to maintain working capital, equity capital or any other
financial statement condition or liquidity of the primary obligor so as to
enable the primary obligor to pay such Indebtedness or other payment obligation,
or (iv) entered into for the purpose of assuring in any other manner the
obligees in respect of such Indebtedness or other payment obligation of the
payment thereof or to protect such obligees against loss in respect thereof (in
whole or in part), or (b) any Lien on any assets of such Person securing any
Indebtedness or other payment obligation of any other Person, whether or not
such Indebtedness or other payment obligation is assumed by such Person;
PROVIDED, HOWEVER, that the term "GUARANTY OBLIGATION" shall not include
endorsements of instruments for deposit or collection in the ordinary course of
business. The amount of any Guaranty Obligation shall be deemed to be the lesser
of (a) an amount equal to the stated or determinable outstanding amount of the
related primary obligation and (b) the maximum amount for which such guarantying
Person may be liable pursuant to the terms of the instrument embodying such
Guaranty Obligation, unless the outstanding amount of such primary obligation
and the maximum amount for which such guarantying Person may be liable are not
stated or determinable, in which case the amount of such Guaranty Obligation
shall be the maximum reasonably anticipated liability in respect thereof as
determined by the guarantying Person in good faith.

     HAZARDOUS SUBSTANCE means any substance that poses a threat to, or is
regulated to protect, human health, safety, public welfare, or the environment,
including without limitation: (a) any "hazardous substance," "pollutant" or
"contaminant," and any "petroleum" or "natural gas liquids" as those terms are
defined or used under Section 101 of the Comprehensive Environmental Response,
Compensation and Liability Act of 1980, as amended ( 42 U.S.C. Sections 9601 et
seq.) ("CERCLA"), (b)

                                       11
<Page>

"solid waste" as defined by the federal Solid Waste Disposal Act (42 U.S.C.
Sections 6901 et seq.), (c) asbestos or a material containing asbestos, (d) any
material that contains lead or lead-based paint, (e) any item or equipment that
contains or is contaminated by polychlorinated biphenyls, (f) any radioactive
material, (g) urea formaldehyde, (h) putrescible materials, (i) infectious
materials, (j) toxic microorganisms, including mold, or (k) any substance the
presence or Release of which requires reporting, investigation or remediation
under any Environmental Law.

     HONOR DATE has the meaning set forth in SECTION 2.14(c)(i).

     INDEBTEDNESS means, as to any Person at a particular time, all of the
following:

           (a) all obligations of such Person for borrowed money and all
     obligations of such Person evidenced by bonds, debentures, notes, loan
     agreements or other similar instruments;

           (b) the face amount of all letters of credit (including standby and
     commercial), banker's acceptances, Bank Guaranties, surety bonds, and
     similar instruments issued for the account of such Person, and, without
     duplication, all drafts drawn and unpaid thereunder;

           (c) net obligations under any Swap Contract in an amount equal to (i)
     if such Swap Contract has been closed out, the termination value thereof,
     or (ii) if such Swap Contract has not been closed out, the mark-to-market
     value thereof determined on the basis of readily available quotations
     provided by any recognized dealer in such Swap Contract;

           (d) whether or not so included as liabilities in accordance with
     GAAP, all obligations of such Person to pay the deferred purchase price of
     property or services, other than trade accounts payable in the ordinary
     course of business not overdue by more than 60 days, and indebtedness
     (excluding prepaid interest thereon) secured by a Lien on property owned or
     being purchased by such Person (including indebtedness arising under
     conditional sales or other title retention agreements), whether or not such
     indebtedness shall have been assumed by such Person or is limited in
     recourse;

           (e)  Capital Leases and Synthetic Lease Obligations; and

           (f)  all Guaranty Obligations of such Person in respect of any of the
     foregoing.

     For all purposes hereof, the Indebtedness of any Person shall include the
Indebtedness of any partnership or joint venture in which such Person is a
general partner, unless such Indebtedness is expressly made non-recourse to such
Person except for customary exceptions acceptable to the Required Lenders. The
amount of any Capital Lease or Synthetic Lease as of any date shall be deemed to
be the amount of Attributable Indebtedness in respect thereof as of such date.

     INDEMNIFIED LIABILITIES has the meaning set forth in SECTION 10.05.

     INDEMNITEES has the meaning set forth in SECTION 10.05.

     INITIAL FINANCIAL STATEMENTS means the financial statements delivered
pursuant to clauses (A) and (B) of SECTION 4.01(a)(vii).

     INTEREST COVERAGE RATIO means, as of any date of determination, the ratio
of (a) Consolidated EBITDA for the period of the four prior fiscal quarters
ending on such date to (b) the sum of

                                       12
<Page>

(i) Consolidated Interest Charges during such period and (ii) imputed interest
charges on Synthetic Leases, of the MLP and its Subsidiaries during such period.
Consolidated Interest Charges and imputed interest charges on Synthetic Leases
for the fiscal quarters ending June 30, 2002, September 30, 2002, December 31,
2002, and March 31, 2003, shall be computed on an annualized pro forma basis
based upon Consolidated Interest Charges and imputed interest charges on
Synthetic Leases for the period from the MLP Offering Closing through the date
of determination.

     INTEREST PAYMENT DATE means, (a) as to any Loan other than a Base Rate
Loan, the last day of each Interest Period applicable to such Loan; PROVIDED,
HOWEVER, that if any Interest Period for a Eurodollar Rate Loan exceeds three
months, the respective dates that fall every three months after the beginning of
such Interest Period shall also be Interest Payment Dates; and (b) as to any
Base Rate Loan, the last Business Day of each March, June, September and
December and the Maturity Date.

     INTEREST PERIOD means, as to each Eurodollar Rate Loan, the period
commencing on the date such Eurodollar Rate Loan is disbursed or converted to or
continued as a Eurodollar Rate Loan and ending on the date one, two, three or
six months thereafter, as selected by the Borrower in its Borrowing Notice;
PROVIDED that:

           (i) any Interest Period that would otherwise end on a day that is not
     a Business Day shall be extended to the next succeeding Business Day
     unless, in the case of a Eurodollar Rate Loan, such Business Day falls in
     another calendar month, in which case such Interest Period shall end on the
     next preceding Business Day;

           (ii) any Interest Period pertaining to a Eurodollar Rate Loan that
     begins on the last Business Day of a calendar month (or on a day for which
     there is no numerically corresponding day in the calendar month at the end
     of such Interest Period) shall end on the last Business Day of the calendar
     month at the end of such Interest Period; and

           (iii) no Interest Period shall extend beyond the scheduled Maturity
     Date.

     INVESTMENT means, as to any Person, any acquisition or investment by such
Person, whether by means of (a) the purchase or other acquisition of capital
stock or other securities of another Person, (b) a loan, advance or capital
contribution to, guaranty of debt of, or purchase or other acquisition of any
other debt or equity participation or interest in, another Person, including any
partnership or joint venture interest in such other Person, or (c) the purchase
or other acquisition (in one transaction or a series of transactions) of assets
of another Person that constitute a business unit. For purposes of covenant
compliance, the amount of any Investment shall be the amount actually invested,
without adjustment for subsequent increases or decreases in the value of such
Investment, less all returns of principal or equity thereon, and shall, if made
by the transfer or exchange of property other than cash be deemed to have been
made in an amount equal to the fair market value of such property.

     IRS means the United States Internal Revenue Service.

     LAWS means, collectively, all applicable international, foreign, federal,
state and local statutes, treaties, rules, regulations, ordinances, codes and
administrative or judicial precedents or authorities, including the
interpretation or administration thereof by any Governmental Authority charged
with the enforcement, interpretation or administration thereof, and all
applicable administrative orders, licenses, authorizations and permits of, any
Governmental Authority.

                                       13
<Page>

     L/C ADVANCE means, with respect to each Lender, such Lender's participation
in any L/C Borrowing in accordance with its Pro Rata Share.

     L/C BORROWING means an extension of credit resulting from a drawing under
any Letter of Credit which has not been reimbursed on the date when made or
refinanced as a Borrowing.

     L/C CREDIT EXTENSION means, with respect to any Letter of Credit, the
issuance thereof or extension of the expiry date thereof, or the renewal or
increase of the amount thereof.

     L/C ISSUER means Bank of America in its capacity as issuer of Letters of
Credit hereunder, or any successor issuer of Letters of Credit hereunder.

     L/C OBLIGATIONS means, as at any date of determination, the aggregate
undrawn face amount of all outstanding Letters of Credit PLUS the aggregate of
all Unreimbursed Amounts, including all L/C Borrowings.

     LENDER has the meaning specified in the introductory paragraph hereto and,
as the context requires, includes the L/C Issuer.

     LENDER HEDGING AGREEMENT means a Swap Contract between a Company and a
Lender or an Affiliate of a Lender.

     LENDING OFFICE means, as to any Lender, the office or offices of such
Lender set forth on its Administrative Details Form, or such other office or
offices as a Lender may from time to time notify the Borrower and the
Administrative Agent.

     LETTER OF CREDIT means any standby letter of credit issued hereunder.

     LETTER OF CREDIT APPLICATION means an application and agreement for the
issuance or amendment of a letter of credit in the form from time to time in use
by the L/C Issuer.

     LETTER OF CREDIT EXPIRATION DATE means the day that is seven days prior to
the Maturity Date (or, if such day is not a Business Day, the next preceding
Business Day).

     LETTER OF CREDIT SUBLIMIT means an amount equal to the lesser of the
Aggregate Commitments and $3,000,000. The Letter of Credit Sublimit is part of,
and not in addition to, the Aggregate Commitments.

     LEVERAGE RATIO means, for the MLP and its Subsidiaries on a consolidated
basis, the ratio of (a) Consolidated Funded Debt as of the determination date to
(b) Consolidated EBITDA for the period of the four fiscal quarters ending on
such date, or if such date is not the last day of a fiscal quarter, ending on
the last day of the fiscal quarter most recently ended.

     LIEN means any mortgage, pledge, hypothecation, assignment, deposit
arrangement, encumbrance, lien (statutory or other), charge, or preference,
priority or other security interest or preferential arrangement of any kind or
nature whatsoever to secure or provide for payment of any obligation of any
Person, (including any conditional sale or other title retention agreement, any
financing lease having substantially the same economic effect as any of the
foregoing, and the filing of any financing statement under the Uniform
Commercial Code or comparable Laws of any jurisdiction), including the interest
of a purchaser of accounts receivable.

                                       14
<Page>

     LIMITED LIABILITY COMPANY AGREEMENT (BORROWER) means (a) prior to the MLP
Offering Closing, the Limited Liability Company Agreement of the Borrower, dated
January 26, 2002, and (b) after the MLP Offering Closing, the Amended and
Restated Limited Liability Company Agreement of the Borrower, substantially in
the form attached as Exhibit 3.4 to the MLP Registration Statement.

     LOAN means an extension of credit by a Lender to the Borrower pursuant to
SECTION 2.01 or SECTION 2.02.

     LOAN DOCUMENTS means this Agreement, each Note, each of the Collateral
Documents, the Agent/Arranger Fee Letter, each Borrowing Notice, each Compliance
Certificate, the Guaranties, any Subordination Agreement, the Agreement
Regarding Collateral, each Letter of Credit Application, and each other
agreement, document or instrument delivered by the Borrower or any of its
Subsidiaries from time to time in connection with this Agreement and the Notes.

     LOAN PARTY means each of the Borrower, each Guarantor, and each other
entity that is an Affiliate of the Borrower that executes one or more Loan
Documents.

     MARKWEST PARENT means MarkWest Hydrocarbon, Inc., a Delaware corporation.

     MARKWEST PARTY means MarkWest Parent or any Subsidiary of MarkWest Parent,
other than the General Partner, the MLP, the Borrower and its Subsidiaries.

     MATERIAL ADVERSE EFFECT means (a) a material adverse change in, or a
material adverse effect upon, the operations, business, properties or condition
(financial or otherwise) or prospects of the Borrower and its Subsidiaries taken
as a whole or the MLP and its Subsidiaries taken as a whole; (b) a material
impairment of the ability of the Borrower, or any other Loan Party to perform
their obligations under the Loan Documents to which it is a party; or (c) a
material adverse effect upon the legality, validity, binding effect or
enforceability against the Borrower or any other Loan Party of any Loan
Documents.

     MATERIAL AGREEMENTS means the following, which shall be satisfactory to the
Administrative Agent and the Required Lenders: (a) the Omnibus Agreement, (b)
the Contribution Agreement, (c) the Gas Processing Agreement (Kenova, Boldman
and Cobb Plants), the Pipeline Liquids Transportation Agreement, the
Fractionation, Storage and Loading Agreement (Siloam), and the Natural Gas
Liquids Purchase Agreement (Maytown), (d) Gas Processing Agreement (Maytown)
dated May 28, 1989 between Equitable Production Company and Borrower as assignee
of MarkWest Parent, and (e) any other contract material to the business of the
MLP or the Borrower to which the Borrower or any Borrower Affiliate is a party.
"MATERIAL AGREEMENT" means each of such Material Agreements.

     MATURITY DATE means (a) the Stated Maturity Date, or (b) such earlier
effective date of any other termination, cancellation, or acceleration of all
Commitments under this Agreement.

     MAXIMUM AMOUNT and MAXIMUM RATE respectively mean, for each Lender, the
maximum non-usurious amount and the maximum non-usurious rate of interest which,
under applicable Law, such Lender is permitted to contract for, charge, take,
reserve, or receive on the Obligations.

     MIDSTREAM BUSINESSES means gathering and processing of natural gas and the
transportation, fractionation, marketing, and storage of natural gas liquids,
and businesses closely related thereto.

                                       15
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     MLP means MarkWest Energy Partners, L.P., a Delaware limited partnership.

     MLP OFFERING means the initial sale to the public of common units in the
MLP pursuant to the MLP Registration Statement.

     MLP OFFERING CLOSING means the consummation of the sale of common units to
the public pursuant to the MLP Registration Statement.

     MLP REGISTRATION STATEMENT means the Registration Statement on Form S-1
filed on January 31, 2002 with the Securities and Exchange Commission in
connection with the sale of common units in the MLP, as amended on March 22,
2002, and as may be further amended from time to time.

     MORTGAGES means the mortgages, deeds of trust, or similar instruments
executed by any of the Loan Parties in favor of Administrative Agent, for the
benefit of the Lenders, and all supplements, assignments, amendments, and
restatements thereto (or any agreement in substitution therefore, and "MORTGAGE"
means each of such Mortgages).

     MULTIEMPLOYER PLAN means any employee benefit plan of the type described in
SECTION 4001(a)(3) of ERISA, to which the Borrower or any ERISA Affiliate makes
or is obligated to make contributions, or during the preceding three calendar
years, has made or been obligated to make contributions.

     NATURAL GAS LIQUIDS PURCHASE AGREEMENT (MAYTOWN) means the Natural Gas
Liquids Purchase Agreement (Maytown) between MarkWest Energy Appalachia, L.L.C.
and MarkWest Parent dated as of the Conditions Effective Date.

     NET CASH PROCEEDS means (a) with respect to any Disposition, cash
(including any cash received by way of deferred payment as and when received)
received by the Borrower or any of its Subsidiaries in connection with and as
consideration therefor, on or after the date of consummation of such
transaction, AFTER (i) deduction of Taxes payable in connection with or as a
result of such transaction, and (ii) payment of all usual and customary
brokerage commissions and all other reasonable fees and expenses related to such
transaction (including, without limitation, reasonable attorneys' fees and
closing costs incurred in connection with such transaction), and (b) with
respect to any Refinancing Indebtedness, proceeds of such Indebtedness after
payment of all reasonable closing costs.

     NONRENEWAL NOTICE DATE has the meaning specified in SECTION 2.14(b)(iii).

     NOTES means the Revolver Notes and the Term Notes of the Borrower,
substantially in the form of EXHIBIT B-1 and B-2, respectively, hereto,
evidencing the obligation of Borrower to repay the Loans, and "NOTE" means any
one of such promissory notes issued hereunder.

     OBLIGATIONS means all advances to, and debts, liabilities, obligations,
covenants and duties of, any Loan Party arising under any Loan Document, whether
direct or indirect (including those acquired by assumption), absolute or
contingent, due or to become due, now existing or hereafter arising and
including interest that accrues after the commencement by or against any Loan
Party of any proceeding under any Debtor Relief Laws naming such Person as the
debtor in such proceeding. In addition, all references to the "OBLIGATIONS" in
the Collateral Documents and in SECTIONS 2.13 and 10.09 of this Agreement shall,
in addition to the foregoing, also include all present and future indebtedness,
liabilities, and obligations (and all renewals and extensions thereof or any
part thereof) now or hereafter owed to any Lender or any Affiliate of a Lender
arising pursuant to any Lender Hedging Agreement.

                                       16
<Page>

     OBLIGOR means the Borrower or any other Person (other than the
Administrative Agent or any Lender) obligated under any Loan Document.

     OMNIBUS AGREEMENT means the Omnibus Agreement dated as of the date of the
MLP Offering Closing, among the MLP, the Borrower, and MarkWest Parent.

     ORGANIZATION DOCUMENTS means, (a) with respect to any corporation, the
certificate or articles of incorporation and the bylaws; (b) with respect to any
limited liability company, the certificate of formation and operating agreement;
and (c) with respect to any partnership, joint venture, trust or other form of
business entity, the partnership, joint venture or other applicable agreement of
formation and any agreement, instrument, filing or notice with respect thereto
filed in connection with its formation with the secretary of state or other
department in the state of its formation, in each case as amended from time to
time.

     OTHER TAXES has the meaning specified in SECTION 3.01(b).

     OUTSTANDING AMOUNT on any date (i) with respect to Loans, means the
aggregate principal amount thereof after giving effect to any Borrowings and
prepayments or repayments occurring on such date, (ii) with respect to any L/C
Obligations, the amount of such L/C Obligations on such date after giving effect
to any L/C Credit Extension occurring on such date and any other changes in the
aggregate amount of the L/C Obligations as of such date, including as a result
of any reimbursements of outstanding unpaid drawings under any Letters of Credit
or any reductions in the maximum amount available for drawing under Letters of
Credit taking effect on such date, and (iii) for purposes of SECTION 2.11(d)
with respect to Obligations under a Lender Hedging Agreement, means the amount
then due and payable under such Lender Hedging Agreement.

     OVERALLOTMENT means an option for 300,000 common units of the MLP,
exercised by the underwriters, such that an aggregate of 2,300,000 common units
of the MLP are purchased in the MLP Offering.

     PARENT CHANGE OF CONTROL means (a) the acquisition by any person or entity,
or two or more persons or entities acting in concert (other than John Fox and
members of his family), of beneficial ownership (within the meaning of Rule
13d-3 of the Securities and Exchange Commission under the Securities Exchange
Act of 1934) of 30% or more of the outstanding shares of voting stock of
MarkWest Parent or (b) the failure of John Fox and members of his family to own,
free and clear of all Liens or other encumbrances, at least 25% of the
outstanding shares of voting stock of MarkWest Parent on a fully diluted basis.

     PARENT CREDIT AGREEMENT means the Fifth Amended and Restated Credit
Agreement dated as of the Conditions Effective Date executed by the MarkWest
Parent, Bank of America, N.A., as Administrative Agent and as a Lender, and the
other Lenders parties thereto, as the same may from time to time be amended and
restated.

     PARENT MATERIAL AGREEMENTS means (a) the Kenova Operating Agreement dated
as of October 16, 1999 between Columbia Gas Transmission Corporation and
MarkWest Parent, (b) the Agreement dated as of October 15, 1999 between Columbia
Gas Transmission Corporation, Columbia Natural Resources, Inc. and MarkWest
Parent, (c) Letter Agreement dated October 16, 1999 between Columbia Gas
Transmission Corporation and MarkWest Parent, (d) Gas Processing Agreement dated
May 20, 1997 between Columbia Natural Resources, Inc. and MarkWest Parent, as
amended by Amendment No. 1 to

                                       17
<Page>

Processing Agreement dated October 15, 1999, and (e) each other material
contract or other agreement to which a MarkWest Party is a party and (1) which
involves the processing of natural gas using facilities owned by a Company or
(2) otherwise relates to the business of a Company.

     PARTICIPANT has the meaning specified in SECTION 10.07(d).

     PARTNERSHIP AGREEMENT (MLP) means (a) prior to the MLP Offering Closing,
the Partnership Agreement of the MLP dated January 25, 2002, and (b) after the
MLP Offering Closing, the First Amended and Restated Agreement of Limited
Partnership of the MLP, substantially in the form attached as Appendix A to the
MLP Registration Statement.

     PBGC means the Pension Benefit Guaranty Corporation.

     PENSION PLAN means any "EMPLOYEE PENSION BENEFIT PLAN" (as such term is
defined in SECTION 3(2)(A) of ERISA), other than a Multiemployer Plan, that is
subject to TITLE IV of ERISA and is sponsored or maintained by the Borrower or
any ERISA Affiliate or to which the Borrower or any ERISA Affiliate contributes
or has an obligation to contribute, or in the case of a multiple employer plan
(as described in SECTION 4064(a) of ERISA) has made contributions at any time
during the immediately preceding five plan years.

     PERMITTED ACQUISITION means an Acquisition by the Borrower or a Subsidiary
of the Borrower resulting in ownership of assets inside the United States or
Canada, or of equity interests in a Domestic Person, so long as the following
requirements have been satisfied:

           (i) If such Acquisition results in the Borrower's ownership of a
     Subsidiary, the Borrower shall have complied with the requirements of
     SECTIONS 6.15 and 6.16 as of the date of such Acquisition;

           (ii) If the Purchase Price for such Acquisition, when added to the
     purchase price for all Acquisitions made during the most recent twelve (12)
     calendar months (including the calendar month in which such Acquisition is
     closed), equals or exceeds $10,000,000, then not less than fourteen (14)
     days prior to the closing of such Acquisition, the Borrower shall deliver
     to the Administrative Agent a certificate of a Responsible Officer of the
     Borrower demonstrating pro forma compliance with SECTIONS 7.01, 7.04 and
     7.15, as of the closing of such Acquisition after giving effect thereto and
     after giving effect to any Indebtedness (including Obligations) incurred in
     connection therewith;

           (iii) With respect to Acquisitions involving acquisitions of an
     equity interest, such Acquisition shall have been approved or consented to
     by the board of directors or similar governing entity of the Person being
     acquired; and

           (iv) As of the closing of such Acquisition no Default or Event of
     Default shall exist or occur as a result of, and after giving effect to,
     such Acquisition.

     PERMITTED LIENS means Liens permitted under SECTION 7.01 as described in
such Section.

     PERSON means any individual, trustee, corporation, general partnership,
limited partnership, limited liability company, joint stock company, trust,
unincorporated organization, bank, business association, firm, joint venture or
Governmental Authority.

                                       18
<Page>

     PIPELINE LIQUIDS TRANSPORTATION AGREEMENT means the Pipeline Liquids
Transportation Agreement between MarkWest Energy Appalachia, L.L.C. and MarkWest
Parent dated as of the Conditions Effective Date.

     PLAN means any "EMPLOYEE BENEFIT PLAN" (as such term is defined in SECTION
3(3) of ERISA) established by the Borrower or any ERISA Affiliate.

     PRINCIPAL PAYMENT means a payment of principal (or, in the case of a
Capitalized Lease or a Synthetic Lease, Attributable Indebtedness), whether
pursuant to an amortization schedule, at maturity, or otherwise.

     PRO RATA SHARE means, at any date of determination, for any Lender, the
percentage (carried out to the ninth decimal place) that its Committed Sum bears
to the Aggregate Committed Sum.

     PROCEEDS ACCOUNT has the meaning set forth in SECTION 2.04(b)(iii).

     PURCHASE PRICE means, with respect to any Acquisition, all direct,
indirect, and deferred cash and non-cash payments made to or for the benefit of
the Person being acquired (or whose assets are being acquired), its
shareholders, officers, directors, employees, or Affiliates in connection with
such Acquisition, including, without limitation, the amount of any Indebtedness
being assumed in connection with such Acquisition and (subject to the
limitations on Indebtedness hereunder) seller financing, payments under
non-competition or consulting agreements entered into in connection with such
Acquisition and similar agreements, all non-cash consideration and the value of
any stock, options, or warrants or other rights to acquire stock issued as part
of the consideration in such transaction.

     PURCHASED ASSETS means the assets purchased from MarkWest Parent and its
subsidiaries and transferred to the MLP, the Borrower, and their respective
subsidiaries pursuant to the Contribution Agreement.

     QUARTERLY DISTRIBUTIONS means with respect to the Borrower, the
distributions by the Borrower of Available Cash (as defined in the Limited
Liability Company Agreement (Borrower)) or with respect to MLP, the
distributions by the MLP of Available Cash (as defined in the Partnership
Agreement (MLP)).

     REDUCTION AMOUNT has the meaning set forth in the definition of TRIGGERING
SALE.

     REFINANCING INDEBTEDNESS has the meaning set forth in SECTION 7.04(b).

     REGISTER has the meaning set forth in SECTION 10.07(c).

     REINVESTED means used for capital expenditures or Acquisitions in
connection with the Midstream Business of a Company.

     RELATED PARTIES means, with respect to any specified Person, such Person's
Affiliates and the respective directors, officers, employees, agents and
advisors of such Person and such Person's Affiliate.

     RELEASE means any spilling, leaking, pumping, pouring, emitting, emptying,
discharging, injecting, escaping, leaching, dumping, disposal, deposit,
dispersal, migrating, or other movement into the air, ground, or surface water,
or soil.

                                       19
<Page>

     REPORTABLE EVENT means any of the events set forth in SECTION 4043(c) OF
ERISA, other than events for which the 30 day notice period has been waived.

     REQUEST FOR CREDIT EXTENSION means (a) with respect to a Borrowing,
conversion or continuation of Loans, a Borrowing Notice, and (b) with respect to
an L/C Extension, a Letter of Credit Application.

     REQUIRED LENDERS means (a) on any date of determination on and after the
Closing Date and prior to the date of the initial Borrowing, those Lenders
holding more than 66 2/3% of the Revolver Commitment, (b) on any date of
determination on and after the date of the initial Borrowing and prior to the
Maturity Date, those Lenders holding more than 66 2/3% of the SUM of (i) the
Revolver Commitment PLUS (ii) the Term Loan Principal Debt; and (c) on any date
of determination on or after the Maturity Date, those Lenders holding more than
66 2/3% of the Outstanding Amount of Loans.

     REQUIRED REVOLVER LENDERS means (a) on any date of determination on and
after the Closing Date and prior to the date of the initial Borrowing, those
Lenders holding more than 66 2/3% of the (i) Acquisition Subfacility Commitment
and (ii) Working Capital/Distribution Subfacility Committed Sum (b) on any date
of determination on and after the date of the initial Borrowing and prior to the
Maturity Date, those Lenders holding more than 66 2/3% of the Revolver
Commitment; and (c) on any date of determination on or after the Maturity Date,
those Lenders holding more than 66 2/3% of the Revolver Principal Debt.

     REQUIRED TERM LENDERS means (a) on any date of determination on and after
the Closing Date and prior to the date of the initial Borrowing, those Lenders
holding more than 66 2/3% of the Term Loan Facility Committed Sum (b) on any
date of determination on and after the date of the initial Borrowing and prior
to the Maturity Date, those Lenders holding more than 66 2/3% of the Term Loan
Commitment; and (c) on any date of determination on or after the Maturity Date,
those Lenders holding more than 66 2/3% of the Term Loan Principal Debt.

     RESPONSIBLE OFFICER means the president, chief executive officer, vice
president, chief financial officer, controller, treasurer or assistant treasurer
of a Person. Any document delivered hereunder that is signed by a Responsible
Officer of a Loan Party shall be conclusively presumed to have been authorized
by all necessary corporate, partnership, limited liability company, and/or other
action on the part of such Loan Party and such Responsible Officer shall be
conclusively presumed to have acted on behalf of such Loan Party.

     RESTRICTED PAYMENT by a Person means any dividend or other distribution
(whether in cash, securities or other property) with respect to any equity
interest in such Person, or any payment (whether in cash, securities or other
property), including any sinking fund or similar deposit on account of the
purchase, redemption, retirement, acquisition, cancellation or termination of
any such equity interest or of any option, warrant or other right to acquire any
such equity interest.

     REVOLVER COMMITMENT means an amount (subject to reduction or cancellation
as herein provided) equal to the sum of (i) the Working Capital/Distribution
Subfacility Commitment, plus (ii) the Acquisition Subfacility Commitment, or as
the context may require, means the Lenders' commitments to make Loans under the
Revolver Facility pursuant to SECTION 2.01.

     REVOLVER FACILITY means the credit facility as described in and subject to
the limitations set forth in SECTION 2.01.

                                       20
<Page>

     REVOLVER NOTE means a promissory note in substantially the form of EXHIBIT
B-1, and all renewals and extensions of all or any part thereof.

     REVOLVER PRINCIPAL DEBT means, on any date of determination, the aggregate
unpaid principal balance of all Loans under the Revolver Facility.

     RIGHTS means rights, remedies, powers, privileges, and benefits.

     SECURITY AGREEMENTS means, collectively, the security agreements, or
similar instruments, executed by any of the Loan Parties in favor of the
Administrative Agent for the benefit of the Lenders, and all supplements,
assignments, amendments, and restatements thereto (or any agreement in
substitution therefore), and "SECURITY AGREEMENT" means each of such Security
Agreements.

     STATED MATURITY DATE means May 19, 2005.

     SUBSIDIARY of a Person means a corporation, partnership, joint venture,
limited liability company or other business entity of which a majority of the
shares of securities or other interests having ordinary voting power for the
election of directors or other governing body (other than securities or
interests having such power only by reason of the happening of a contingency)
are at the time beneficially owned, or the management of which is otherwise
controlled, directly, or indirectly through one or more intermediaries, or both,
by such Person. Unless otherwise specified, all references herein to a
"SUBSIDIARY" or to "SUBSIDIARIES" shall refer to a Subsidiary or Subsidiaries of
the Borrower.

     SUBORDINATION AGREEMENT has the meaning set forth in SECTION 7.04(b).

     SWAP CONTRACT means (a) any and all rate swap transactions, basis swaps,
credit derivative transactions, forward rate transactions, commodity swaps,
commodity options, forward commodity contracts, equity or equity index swaps or
options, bond or bond price or bond index swaps or options or forward bond or
forward bond price or forward bond index transactions, interest rate options,
forward foreign exchange transactions, cap transactions, floor transactions,
collar transactions, currency swap transactions, cross-currency rate swap
transactions, currency options, spot contracts, or any other similar
transactions or any combination of any of the foregoing (including any options
to enter into any of the foregoing), whether or not any such transaction is
governed by or subject to any master agreement, and (b) any and all transactions
of any kind, and the related confirmations, which are subject to the terms and
conditions of, or governed by, any form of master agreement published by the
International Swaps and Derivatives Association, Inc., any International Foreign
Exchange Master Agreement, or any other master agreement (any such master
agreement, together with any related schedules, a "MASTER AGREEMENT"), including
any such obligations or liabilities under any Master Agreement.

     SWAP TERMINATION VALUE means, in respect of any one or more Swap Contracts,
after taking into account the effect of any legally enforceable netting
agreement relating to such Swap Contracts, (a) for any date on or after the date
such Swap Contracts have been closed out and termination value(s) determined in
accordance therewith, such termination value(s), and (b) for any date prior to
the date referenced in clause (a) the amount(s) determined as the mark-to-market
value(s) for such Swap Contracts, as determined based upon one or more
mid-market or other readily available quotations provided by any recognized
dealer in such Swap Contracts (which may include any Lender).

     SYNTHETIC LEASE OBLIGATION means the monetary obligation of a Person under
(a) a so-called synthetic or tax retention lease, or (b) an agreement for the
use or possession of property creating obligations that do not appear on the
balance sheet of such Person but which are depreciated for tax

                                       21
<Page>

purposes by such Person. The amount of any Synthetic Lease Obligation as of any
date shall be deemed to be the amount of Attributable Indebtedness in respect
thereof as of such date.

     TAXES has the meaning set forth in SECTION 3.01.

     TERM LOAN COMMITMENT means an amount (subject to reduction or cancellation
as herein provided) equal to $21,400,000.

     TERM LOAN FACILITY means the credit facility as described in and subject to
the limitations set forth in SECTION 2.02.

     TERM NOTE means a promissory note substantially in the form of EXHIBIT B-2,
and all renewals and extensions of all or any part thereof.

     TERM LOAN PRINCIPAL DEBT means, on any date of determination, the aggregate
unpaid principal balance of all Loans under the Term Loan Facility.

     THRESHOLD AMOUNT at any time means an amount equal to 5% of the MLP's
consolidated assets measured as of the close of the then most recent fiscal
quarter end.

     TRIGGERING SALE means any Disposition (including sales of stock of
Subsidiaries) (other than a Disposition permitted by SECTION 7.07(a) or (b)) by
the Borrower or any Subsidiary of the Borrower to any other Person (other than
to the Borrower or to a Wholly-Owned Subsidiary of the Borrower) with respect to
which the Net Cash Proceeds realized by any Company for such Disposition, when
aggregated with the Net Cash Proceeds from all such other Dispositions by all
Companies occurring since the Closing Date, equals or exceeds the Threshold
Amount. The portion of the Net Cash Proceeds in excess of the Threshold Amount
is herein called the "REDUCTION AMOUNT."

     TYPE means, with respect to a Loan, its character as a Base Rate Loan or a
Eurodollar Rate Loan.

     UNAUTHORIZED ASSIGNMENT means (a) an assignment by a MarkWest Party to any
Person other than another MarkWest Party of any of its rights or obligations
under a Material Agreement or under a Parent Material Agreement other than the
granting of Liens to secure the Parent Credit Facility if such assignment could
reasonably be expected to have a Material Adverse Effect, or (b) a holder of
Liens shall foreclose or there shall occur a transfer in lieu of foreclosure or
other involuntary transfer of any interests of a MarkWest Party in a Material
Agreement or in a Parent Material Agreement if such foreclosure could reasonably
be expected to have (i) a material adverse effect on the ability of such
MarkWest Party (or its successor) to perform its obligations under such
contract, or (ii) a Material Adverse Effect, or (c) the occurrence of any event
or condition that permits the holder of any Indebtedness of a MarkWest Party to
foreclose its Liens on any interests of a MarkWest Party in any Material
Agreement or any Parent Material Agreement if such foreclosure could reasonably
be expected to have (i) a material adverse effect on the ability of such
MarkWest Party (or its successor) to perform its obligations under such
contract, or (ii) a Material Adverse Effect.

     UNFUNDED PENSION LIABILITY means the excess of a Pension Plan's benefit
liabilities under SECTION 4001(a)(16) of ERISA, over the current value of that
Pension Plan's assets, determined in accordance with the assumptions used for
funding the Pension Plan pursuant to SECTION 412 of the Code for the applicable
plan year.

     UNREIMBURSED AMOUNT has the meaning set forth in SECTION 2.14(c)(i).

                                       22
<Page>

     U.S. CREDIT AGREEMENT means the Fifth Amended and Restated Credit Agreement
among, MarkWest Parent, Bank of America, as administrative agent, and the
lenders thereto, dated as of even date herewith as may be amended from time to
time.

     VOTING STOCK means the capital stock (or equivalent thereof) of any class
or kind, of a Person, the holders of which are entitled to vote for the election
of directors, managers, or other voting members of the governing body of such
Person.

     WHOLLY-OWNED when used in connection with a Person means any Subsidiary of
such Person of which all of the issued and outstanding equity interests (EXCEPT
shares required as directors' qualifying shares) shall be owned by such Person
or one or more of its Wholly-Owned Subsidiaries.

     WORKING CAPITAL/DISTRIBUTION SUBFACILITY has the meaning specified in
SECTION 2.01(c).

     WORKING CAPITAL/DISTRIBUTION SUBFACILITY COMMITMENT means an amount
(subject to reduction or cancellation as herein provided) equal to $10,000,000.

     1.02  OTHER INTERPRETIVE PROVISIONS.

     (a) The meanings of defined terms are equally applicable to the singular
and plural forms of the defined terms.

     (b) (i) The words "HEREIN" and "HEREUNDER" and words of similar import when
used in any Loan Document shall refer to such Loan Document as a whole and not
to any particular provision thereof.

           (ii) Unless otherwise specified herein, Article, Section, Exhibit and
     Schedule references are to this Agreement.

           (iii) The term "INCLUDING" is by way of example and not limitation.

           (iv) The term "DOCUMENTS" includes any and all instruments,
     documents, agreements, certificates, notices, reports, financial statements
     and other writings, however evidenced.

     (c) In the computation of periods of time from a specified date to a later
specified date, the word "FROM" means "FROM AND INCLUDING;" the words "TO" and
"UNTIL" each mean "TO BUT EXCLUDING;" and the word "THROUGH" means "TO AND
INCLUDING."

     (d) Section headings herein and the other Loan Documents are included for
convenience of reference only and shall not affect the interpretation of this
Agreement or any other Loan Document.

     1.03  ACCOUNTING TERMS.

     All accounting terms not specifically or completely defined herein shall be
construed in conformity with, and all financial data required to be submitted
pursuant to this Agreement shall be prepared in conformity with, GAAP applied on
a consistent basis, as in effect from time to time, applied in a manner
consistent with that used in preparing the audited financial statements, EXCEPT
as otherwise specifically prescribed herein.

                                       23
<Page>

     1.04 ROUNDING. Any financial ratios required to be maintained by the
Borrower pursuant to this Agreement shall be calculated by dividing the
appropriate component by the other component, carrying the result to one place
more than the number of places by which such ratio is expressed herein and
rounding the result up or down to the nearest number (with a rounding-up if
there is no nearest number).

     1.05 REFERENCES TO AGREEMENTS AND LAWS. Unless otherwise expressly provided
herein, (a) references to agreements (including the Loan Documents) and other
contractual instruments shall be deemed to include all subsequent amendments,
restatements, extensions, supplements and other modifications thereto, but only
to the extent that such amendments, restatements, extensions, supplements and
other modifications are not prohibited by any Loan Document; and (b) references
to any Law shall include all statutory and regulatory provisions consolidating,
amending, replacing, supplementing or interpreting such Law.

                                   ARTICLE II.
                         THE COMMITMENTS AND BORROWINGS

     2.01 REVOLVER LOANS. (a) Subject to and in reliance upon the terms,
conditions, representations, and warranties in the Loan Documents, each Lender
severally, but not jointly, agrees to make loans (each such Loan a "LOAN") to
Borrower from time to time on any Business Day during the period from the
Conditions Effective Date to the Maturity Date, in an aggregate amount not to
exceed at any time outstanding the amount of such Lender's Pro Rata Share of one
or more Borrowings under (i) the Acquisition Subfacility (further described in
SECTION 2.01(b) below) not to exceed such Lender's Committed Sum under the
Acquisition Subfacility, and (ii) the Working Capital/Distribution Subfacility
(further described in SECTION 2.01(c) below) not to exceed, when aggregated with
the Outstanding Amount of the L/C Obligations, such Lender's Committed Sum under
the Working Capital/Distribution Subfacility. Such Borrowings may be repaid and
reborrowed from time to time in accordance with the terms and provisions of the
Loan Documents; PROVIDED THAT, each such Borrowing must occur on a Business Day
and no later than the Business Day immediately preceding the Maturity Date.

     (b) Loans under the Acquisition Subfacility shall be available to Borrower
for the purposes set forth in SECTION 6.12(b). After giving effect to any
Borrowing under the Acquisition Subfacility, the aggregate Outstanding Amount of
all Loans under the Acquisition Subfacility shall not exceed the Acquisition
Subfacility Commitment then in effect.

     (c) Loans under the Working Capital/Distribution Subfacility shall be
available to Borrower for the purposes set forth in SECTION 6.12(c); PROVIDED,
HOWEVER, Borrowings under the Working Capital/Distribution Subfacility will be
available to fund not more than $2,250,000 in Distribution Loans in any four (4)
consecutive fiscal quarters. After giving effect to any Borrowing under the
Working Capital/Distribution Subfacility, the aggregate Outstanding Amount of
all Loans and L/C Obligations under the Working Capital/Distribution Subfacility
shall not exceed the Working Capital/Distribution Subfacility Commitment then in
effect.

     2.02 TERM LOAN FACILITY. Subject to and in reliance upon the terms,
conditions, representations, and warranties in the Loan Documents, each Lender
severally, but not jointly, agrees to make Loans to Borrower in a single
disbursement on the Conditions Effective Date in aggregate amount not to exceed
at any time outstanding the amount of such Lender's Pro Rata Share of the Term
Loan Commitment. If all or a portion of the Term Loan Principal Debt is paid or
prepaid, then the amount so paid or prepaid may not be reborrowed. Any portion
of the Term Loan Commitment that remains

                                       24
<Page>

undisbursed after the initial disbursement under the Term Loan Facility shall be
reduced to zero and cancelled on the date of such initial disbursement.

     2.03  BORROWINGS, CONVERSIONS AND CONTINUATIONS OF LOANS.

     (a) Each Borrowing, each conversion of Loans from one Type to the other,
and each continuation of Loans as the same Type shall be made upon the
Borrower's irrevocable notice to the Administrative Agent, which may be given by
telephone. Each such notice must be received by the Administrative Agent not
later than 10:00 a.m., Dallas, Texas time, (i) three Business Days prior to the
requested date of any Borrowing of, conversion to or continuation of Eurodollar
Rate Loans, and (ii) one Business Day prior to the conversion of Eurodollar Rate
Loans to Base Rate Loans, or the requested date of any Borrowing of Base Rate
Loans. Each such telephonic notice must be confirmed promptly by delivery to the
Administrative Agent of a written Borrowing Notice, appropriately completed and
signed by an authorized officer of the Borrower. Each Borrowing of, conversion
to or continuation of Eurodollar Rate Loans shall be in a principal amount of
$500,000 or a whole multiple of $500,000 in excess thereof. Each Borrowing of or
conversion to Base Rate Loans shall be in a principal amount of $500,000 or a
whole multiple of $100,000 in excess thereof. Each Borrowing Notice (whether
telephonic or written) shall specify (i) whether the Borrowing, conversion or
continuation (as applicable) is under the Term Loan Facility, the Acquisition
Subfacility or the Working Capital/Distribution Subfacility, (ii) whether the
Borrower is requesting a Borrowing, a conversion of Loans from one Type to the
other, or a continuation of Loans as the same Type, (iii) the requested date of
the Borrowing, conversion or continuation, as the case may be (which shall be a
Business Day), (iv) the principal amount of Loans to be borrowed, converted or
continued, (v) the Type of Loans to be borrowed or to which existing Loans are
to be converted, and (vi) if applicable, the duration of the Interest Period
with respect thereto. If the Borrower fails to specify a Type of Loan in a
Borrowing Notice or if the Borrower fails to give a timely notice requesting a
conversion or continuation, then the applicable Loans shall be made or continued
as, or converted to, Base Rate Loans. Any such automatic conversion to Base Rate
Loans shall be effective as of the last day of the Interest Period then in
effect with respect to the applicable Eurodollar Rate Loans. If the Borrower
requests a Borrowing of, conversion to, or continuation of Eurodollar Rate Loans
in any such Borrowing Notice, but fails to specify an Interest Period, it will
be deemed to have specified an Interest Period of one month.

     (b) Following receipt of a Borrowing Notice, the Administrative Agent shall
promptly notify each Lender of its Pro Rata Share of the applicable Loans, and
if no timely notice of a conversion or continuation is provided by the Borrower,
the Administrative Agent shall notify each Lender of the details of any
automatic conversion to Base Rate Loans described in the preceding subsection.
In the case of a Borrowing, each Lender shall make the amount of its Loan
available to the Administrative Agent in immediately available funds at the
Administrative Agent's Office not later than 12:00 Noon, Dallas, Texas time, on
the Business Day specified in the applicable Borrowing Notice. Upon satisfaction
of the applicable conditions set forth in SECTION 4.03 (and, if such Borrowing
is the initial Borrowing, SECTION 4.01), the Administrative Agent shall make all
funds so received available to the Borrower in like funds as received by the
Administrative Agent either by (i) crediting the account of the Borrower on the
books of Bank of America with the amount of such funds or (ii) wire transfer of
such funds, in each case in accordance with instructions provided to the
Administrative Agent by the Borrower; PROVIDED, HOWEVER, that if, on the date of
the Borrowing there are L/C Borrowings outstanding, then the proceeds of such
Borrowing shall be applied, FIRST, to the payment in full of any such L/C
Borrowings, and SECOND, to the Borrower as provided above.

     (c)   Except as otherwise provided herein, a Eurodollar Rate Loan may be
continued or converted only on the last day of the Interest Period for such
Eurodollar Rate Loan. During the existence

                                       25
<Page>

of a Default or Event of Default, no Loans may be requested as, converted to or
continued as Eurodollar Rate Loans without the consent of the Required Lenders,
and the Required Lenders may demand that any or all of the then outstanding
Eurodollar Rate Loans be converted immediately to Base Rate Loans.

     (d) The Administrative Agent shall promptly notify the Borrower and the
Lenders of the interest rate applicable to any Eurodollar Rate Loan upon
determination of such interest rate. The determination of the Eurodollar Rate by
the Administrative Agent shall be conclusive in the absence of manifest error.

     (e) After giving effect to all Borrowings, all conversions of Loans from
one Type to the other, and all continuations of Loans as the same Type, there
shall not be more than six (6) Interest Periods in effect at any given time with
respect to Loans.

     2.04  PREPAYMENTS.

     (a) OPTIONAL PREPAYMENTS. The Borrower may, upon notice to the
Administrative Agent, at any time or from time to time voluntarily prepay in
whole or in part Loans outstanding under the Acquisition Subfacility, the
Working Capital/Distribution Subfacility and/or the Term Loan Principal Debt
without premium or penalty; PROVIDED that (i) such notice must be received by
the Administrative Agent not later than 10:00 a.m., Dallas, Texas time, (A)
three Business Days prior to any date of prepayment of Eurodollar Rate Loans,
and (B) the date of prepayment of Base Rate Loans; (ii) any prepayment of
Eurodollar Rate Loans shall be in a principal amount of $500,000 or a whole
multiple of $500,000 in excess thereof; and (iii) any prepayment of Base Rate
Loans shall be in a principal amount of $500,000 or a whole multiple of $100,000
in excess thereof. Each such notice shall specify the date and amount of such
prepayment and the Type(s) of Loans to be prepaid. The Administrative Agent will
promptly notify each Lender of its receipt of each such notice, and of such
Lender's Pro Rata Share of such prepayment. If such notice is given by the
Borrower, the Borrower shall make such prepayment and the payment amount
specified in such notice shall be due and payable on the date specified therein.
Any prepayment of a Eurodollar Rate Loan shall be accompanied by all accrued
interest thereon, together with any additional amounts required pursuant to
SECTION 3.05. Each such prepayment shall be applied to the Loans of the Lenders
in accordance with their respective Pro Rata Shares.

     Unless a Default or Event of Default has occurred and is continuing or
would arise as a result thereof any payment or prepayment of the Loans may be
reborrowed by Borrower, subject to the terms and conditions hereof.

     (b)   MANDATORY PREPAYMENTS FROM NET CASH PROCEEDS.

           (i) If any portion of the Net Cash Proceeds realized by a Company
     from any Triggering Sale (including any deferred purchase price therefore)
     has not been Reinvested within ninety (90) days from the receipt by such
     Company of such Net Cash Proceeds (including receipt of any deferred
     payments for any such Triggering Sale or portion thereof, if and when
     received), then on the Business Day following such ninetieth (90th) day the
     Commitments shall be permanently reduced, and the Loans shall be prepaid,
     in an amount equal to the portion of the Reduction Amount that is not so
     Reinvested. Net Cash Proceeds of a Disposition that equal, when aggregated
     with Net Cash Proceeds of all Dispositions since the Closing Date, an
     amount less than the Threshold Amount shall not be required to be used for
     mandatory prepayments or commitment reductions pursuant to this SECTION
     2.04(b).

                                       26
<Page>

           (ii) If any Net Cash Proceeds are received from the issuance or
     incurrence of Refinancing Indebtedness by a Company, the Commitments shall
     be permanently reduced, and the Loans shall be prepaid, immediately upon
     receipt of such Net Cash Proceeds, in an amount equal to the amount of Net
     Cash Proceeds received from such Refinancing Indebtedness.

           (iii) Upon receipt by any Company of Net Cash Proceeds from a
     Triggering Sale, the Borrower shall (or shall cause the applicable Company
     to) deposit an amount equal to the Reduction Amount into an account with
     the Administrative Agent (the "PROCEEDS ACCOUNT"); PROVIDED, HOWEVER, that
     the Borrower shall not be required to deposit an amount that is more than
     the amount of the Commitments. Such Reduction Amount shall remain in the
     Proceeds Account until the earlier of (x) the date such Reduction Amount is
     Reinvested, or (y) the ninetieth (90th) day following the receipt of such
     Reduction Amount. If such Reduction Amount is not Reinvested as herein
     provided, such proceeds shall, on the Business Day following such ninetieth
     day, be used for prepayment of Loans and any excess shall be refunded to
     the Borrower, or, if there are no outstanding Loans or unpaid outstanding
     Obligations then due, such Reduction Amount shall be refunded to the
     Borrower, and the Commitments shall be permanently reduced as provided in
     SECTION 2.04(b)(i); PROVIDED, HOWEVER, that if the outstanding Loans are
     Eurodollar Rate Loans, the Administrative Agent shall hold such proceeds in
     the Proceeds Account until the Eurodollar Rate Loans can be prepaid without
     incurring funding losses under SECTION 3.05; PROVIDED, FURTHER, that if the
     Loans have become due and payable pursuant to SECTION 8.02 or otherwise,
     the Administrative Agent may, without notice, apply all funds in the
     Proceeds Account to repayment of the Obligations.

           (iv) The prepayments and commitment reductions provided for in this
     SECTION 2.04(b) shall be applied as follows, UNLESS a Default or Event of
     Default has occurred and is continuing or would arise as a result thereof
     (whereupon the provisions of SECTION 2.11(d) shall apply): (A) first, as a
     payment of all Unreimbursed Amounts then outstanding, until paid in full,
     (B) second, as a repayment of the Term Loan Principal Debt, until paid in
     full, and (C) third, as a repayment of Revolver Principal Debt, to be
     allocated between the Acquisition Subfacility and the Working
     Capital/Distribution Subfacility as specified by the Borrower, or if the
     Borrower fails to so specify or if a Default or Event of Default exists, as
     specified by the Administrative Agent or the Required Banks.

           (v) All funds held in the Proceeds Account shall be invested in time
     deposits or certificates of deposit issued by the Administrative Agent or
     in investments that constitute Cash Equivalents (provided that the
     maturities thereof shall not exceed 90 days). All interest and income
     earned on the amounts held in the Proceeds Account shall be paid to the
     Borrower at the time the funds therein are applied as provided in this
     SECTION 2.04(b).

           (vi) The Borrower hereby grants to the Administrative Agent, for the
     benefit of the Lenders, a lien on and security interest in and to the
     Proceeds Account and all monies, cash, checks, drafts, certificates of
     deposit, instruments, investment property, and other items received by
     Administrative Agent for deposit therein and held therein, as security for
     the Obligations. The rights granted by this SECTION 2.04(b)(vi) shall be in
     addition to the rights of the Administrative Agent under any statutory
     banker's Lien or the common law right of setoff.

     (c) MANDATORY PAYMENTS/REDUCTIONS. If for any reason the Outstanding Amount
of all Loans and L/C Obligations at any time exceeds the Aggregate Commitments
then in effect, the Borrower shall immediately prepay Loans and/or Cash
Collateralize the L/C Obligations in an aggregate amount equal to such excess.

                                       27
<Page>

     (d)   PREPAYMENTS: INTEREST/CONSEQUENTIAL LOSS. All prepayments under this
SECTION 2.04 shall be made TOGETHER WITH accrued interest to the date of such
prepayment on the principal amount prepaid and any amounts due under SECTION
3.05.

     (e)   MANDATORY PREPAYMENTS: CLEAN-DOWN PERIOD. The Borrower shall make
such prepayments of Loans outstanding under the Working Capital/Distribution
Subfacility as are required in order to comply with SECTION 6.14.

     2.05 REDUCTION OR TERMINATION OF COMMITMENTS. The Borrower may, upon notice
to the Administrative Agent, terminate the Aggregate Commitments or (prior to
the Initial Funding Date) permanently reduce the Term Loan Commitment, or
permanently reduce the Revolver Commitment to an amount not less than the sum of
the Outstanding Amount of the then existing (i) Revolver Principal Debt and (ii)
L/C Obligations; PROVIDED THAT (i) any such notice shall be received by the
Administrative Agent not later than 11:00 a.m., five Business Days prior to the
date of termination or reduction, (ii) any such partial reduction shall be in an
aggregate amount of $3,000,000 or any whole multiple of $500,000 in excess
thereof and (iii) any Revolver Commitment reduction shall be allocated between
the Acquisition Subfacility and the Working Capital Distribution Subfacility in
amounts not less than $500,000. The Administrative Agent shall promptly notify
the Lenders of any such notice of reduction or termination. Once reduced in
accordance with this Section, the Commitments may not be increased. Any
reduction of the Revolver Commitment shall be applied to the Commitment of each
Lender according to its Pro Rata Share, and any reduction of the Term Loan
Commitment shall be applied to the Commitment of each Lender according to its
Pro Rata Share. All commitment fees on the portion of the Commitment so
terminated which have accrued to the effective date of any termination of
Commitments shall be paid on the effective date of such termination.

     2.06  REPAYMENT OF LOANS. The Borrower shall repay to the Lenders on the
Maturity Date the aggregate principal amount of Loans outstanding on such date.

     2.07 INTEREST. (a) Subject to the provisions of subsection (b) below, (i)
each Eurodollar Rate Loan shall bear interest on the outstanding principal
amount thereof for each Interest Period at a rate per annum equal to the
Eurodollar Rate for such Interest Period PLUS the Applicable Rate and (ii) each
Base Rate Loan shall bear interest on the outstanding principal amount thereof
from the applicable borrowing date at a rate per annum equal to the Base Rate
PLUS the Applicable Rate.

     (b) While any Event of Default exists or after acceleration, (i) the
Borrower shall pay interest on the principal amount of all outstanding
Obligations at a fluctuating interest rate per annum at all times equal to the
Default Rate to the fullest extent permitted by applicable Law, and (ii) accrued
and unpaid interest on past due amounts (including interest on past due
interest) shall be due and payable upon demand.

     (c) Interest on each Loan shall be due and payable in arrears on each
Interest Payment Date applicable thereto and at such other times as may be
specified herein. Interest hereunder shall be due and payable in accordance with
the terms hereof before and after judgment, and before and after the
commencement of any proceeding under any Debtor Relief Law.

     (d) If the designated rate applicable to any Borrowing exceeds the Maximum
Rate, the rate of interest on such Borrowing shall be limited to the Maximum
Rate, but any subsequent reductions in such designated rate shall not reduce the
rate of interest thereon below the Maximum Rate until the total amount of
interest accrued thereon equals the amount of interest which would have accrued
thereon if

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<Page>

such designated rate had at all times been in effect. In the event that at
maturity (stated or by acceleration), or at final payment of the Outstanding
Amount of any Loans or L/C Obligations, the total amount of interest paid or
accrued is less than the amount of interest which would have accrued if such
designated rates had at all times been in effect, then, at such time and to the
extent permitted by Law, the Borrower shall pay an amount equal to the
difference between (a) the lesser of the amount of interest which would have
accrued if such designated rates had at all times been in effect and the amount
of interest which would have accrued if the Maximum Rate had at all times been
in effect, and (b) the amount of interest actually paid or accrued on such
Outstanding Amount.

     2.08 FEES. (a) COMMITMENT FEE. The Borrower shall pay to the Administrative
Agent for the account of each Lender in accordance with its Pro Rata Share, a
commitment fee equal to the Applicable Rate TIMES the actual daily amount by
which the Aggregate Commitments exceed the Outstanding Amount of Loans. The
commitment fee shall accrue at all times from the Closing Date until the
Maturity Date and shall be due and payable quarterly in arrears on the last
Business Day of each March, June, September and December, commencing with the
first such date to occur after the Closing Date, and on the Maturity Date. The
commitment fee shall be calculated quarterly in arrears, and if there is any
change in the Applicable Rate during any quarter, the actual daily amount shall
be computed and multiplied by the Applicable Rate separately for each period
during such quarter that such Applicable Rate was in effect. The commitment fee
shall accrue at all times, including at any time during which one or more of the
conditions in ARTICLE IV is not met.

     (b) ARRANGER'S AND AGENCY FEES. The Borrower shall pay certain fees to the
Arranger for the Arranger's own account, and shall pay an agency fee to the
Administrative Agent for the Administrative Agent's own account, in the amounts
and at the times specified in the letter agreement, dated March 15, 2002 (the
"AGENT/ARRANGER FEE LETTER"), between the Borrower, the Arrangers and the
Administrative Agent. Such fees shall be fully earned when paid and shall be
nonrefundable for any reason whatsoever.

     (c) LENDERS' UPFRONT FEE. On the Conditions Effective Date, the Borrower
shall pay to the Administrative Agent, for the account of the Lenders in
accordance with their respective Pro Rata Shares, an upfront fee in the agreed
amount in accordance with the Agent/Arranger Fee Letter. Such upfront fees are
for the credit facilities by the Lenders under this Agreement and are fully
earned on the date paid. The upfront fee paid to each Lender is solely for its
own account and is nonrefundable for any reason whatsoever.

     2.09 COMPUTATION OF INTEREST AND FEES. Computation of interest on Base Rate
Loans shall be calculated on the basis of a year of 365 or 366 days, as the case
may be, and the actual number of days elapsed. Computation of all other types of
interest and all fees shall be calculated on the basis of a year of 360 days and
the actual number of days elapsed, which results in a higher yield to the payee
thereof than a method based on a year of 365 or 366 days. Interest shall accrue
on each Loan for the day on which the Loan is made, and shall not accrue on a
Loan, or any portion thereof, for the day on which the Loan or such portion is
paid, PROVIDED that any Loan that is repaid on the same day on which it is made
shall bear interest for one day.

     2.10 EVIDENCE OF DEBT. (a) The Loans made by each Lender shall be evidenced
by one or more accounts or records maintained by such Lender and by the
Administrative Agent in the ordinary course of business. The accounts or records
maintained by the Administrative Agent and each Lender shall be conclusive
absent manifest error of the amount of the Loans made by the Lenders to the
Borrower and the interest and payments thereon. Any failure so to record or any
error in doing so shall not, however, limit or otherwise affect the obligation
of the Borrower hereunder to pay any amount owing with respect to the Loans or
the L/C Obligations. In the event of any conflict between the accounts and

                                       29
<Page>

records maintained by any Lender and the accounts and records of the
Administrative Agent in respect of such matters, the accounts and records of
such Lender shall control. Upon the request of any Lender made through the
Administrative Agent, such Lender's Loans may be evidenced by one or more Notes.
Each Lender may attach schedules to its Note(s) and endorse thereon the date,
Type (if applicable), amount and maturity of the applicable Loans and payments
with respect thereto.

     (b) In addition to the accounts and records referred to in subsection (a),
each Lender and the Administrative Agent shall maintain in accordance with its
usual practice accounts or records evidencing the purchases and sales by such
Lender of participations in Letters of Credit. In the event of any conflict
between the accounts and records maintained by the Administrative Agent and the
accounts and records of any Lender in respect of such matters, the accounts and
records of the Administrative Agent shall control.

     2.11 PAYMENTS GENERALLY. (a) All payments to be made by the Borrower shall
be made without condition or deduction for any counterclaim, defense, recoupment
or setoff. Except as otherwise expressly provided herein, all payments by the
Borrower hereunder shall be made to the Administrative Agent, for the account of
the respective Lenders to which such payment is owed, at the Administrative
Agent's Office in Dollars and in immediately available funds not later than
11:00 a.m., Dallas, Texas time, on the date specified herein. The Administrative
Agent will promptly distribute to each Lender its Pro Rata Share (or other
applicable share as provided herein) of such payment in like funds as received
by wire transfer to such Lender's Lending Office. All payments received by the
Administrative Agent after 11:00 a.m., Dallas, Texas time, shall be deemed
received on the next succeeding Business Day and any applicable interest or fee
shall continue to accrue.

     (b) Subject to the definition of "INTEREST PERIOD," if any payment to be
made by the Borrower shall come due on a day other than a Business Day, payment
shall be made on the next following Business Day, and such extension of time
shall be reflected in computing interest or fees, as the case may be.

     (c) If no Default or Event of Default exists and if no order of application
is otherwise specified in the Loan Documents, payments and prepayments of the
Obligations shall be applied first to fees, second to accrued interest then due
and payable on the Outstanding Amount of Loans and L/C Obligations, and then to
the remaining Obligations in the order and manner as Borrower may direct.

     (d) If at any time insufficient funds are received by and available to the
Administrative Agent to pay fully the Obligations, or if a Default or Event of
Default exists, any payment or prepayment shall be applied in the following
order: (i) to the payment of enforcement expenses incurred by the Administrative
Agent, including Attorney Costs; (ii) to the ratable payment of all other fees,
expenses, and indemnities for which the Administrative Agent or Lenders have not
been paid or reimbursed in accordance with the Loan Documents (as used in this
SECTION 2.11(d)(ii), a "RATABLE PAYMENT" for any Lender or the Administrative
Agent shall be, on any date of determination, that proportion which the portion
of the total fees, expenses, and indemnities owed to such Lender or the
Administrative Agent bears to the total aggregate fees and indemnities owed to
all Lenders and the Administrative Agent on such date of determination); (iii)
to the ratable payment of accrued and unpaid interest on the Outstanding Amount
of Loans and the Outstanding Amount of Obligations under Lender Hedging
Agreements (as used in this SECTION 2.11(d)(iii), "RATABLE PAYMENT" means, for
any Lender (or Lender Affiliate, in the case of Lender Hedging Agreements), on
any date of determination, that proportion which the accrued and unpaid interest
on the Outstanding Amount of Loans and the Outstanding Amount of Obligations
under Lender Hedging Agreements owed to such Lender (or Lender Affiliate, in the
case of Lender Hedging Agreements) bears to the total accrued and unpaid
interest on the Outstanding Amount of Loans

                                       30
<Page>

and the Outstanding Amount of Obligations under Lender Hedging Agreements owed
to all Lenders (and Affiliates, in the case of Lender Hedging Agreements)); (iv)
to the ratable payment of the Outstanding Amount of Loans (as used in this
SECTION 2.11(d)(iv), "RATABLE PAYMENT" means for any Lender, on any date of
determination, that proportion which the Outstanding Amount of Loans owed to
such Lender bears to the Outstanding Amount of Loans owed to all Lenders); (v)
to Cash Collateralize the Letters of Credit, and (vi) to the payment of the
remaining Obligations, if any, in the order and manner the Required Lenders deem
appropriate.

     (e) Unless the Borrower or any Lender has notified the Administrative Agent
prior to the date any payment is required to be made by it to the Administrative
Agent hereunder, that the Borrower or such Lender, as the case may be, will not
make such payment, the Administrative Agent may assume that the Borrower or such
Lender, as the case may be, has timely made such payment and may (but shall not
be so required to), in reliance thereon, make available a corresponding amount
to the Person entitled thereto. If and to the extent that such payment was not
in fact made to the Administrative Agent in immediately available funds, then:

           (i) if the Borrower failed to make such payment, each Lender shall
     forthwith on demand repay to the Administrative Agent the portion of such
     assumed payment that was made available to such Lender in immediately
     available funds, together with interest thereon in respect of each day from
     and including the date such amount was made available by the Administrative
     Agent to such Lender to the date such amount is repaid to the
     Administrative Agent in immediately available funds, at the Federal Funds
     Rate from time to time in effect; and

           (ii) if any Lender failed to make such payment, such Lender shall
     forthwith on demand pay to the Administrative Agent the amount thereof in
     immediately available funds, together with interest thereon for the period
     from the date such amount was made available by the Administrative Agent to
     the Borrower to the date such amount is recovered by the Administrative
     Agent (the "COMPENSATION PERIOD") at a rate per annum equal to the Federal
     Funds Rate from time to time in effect. If such Lender pays such amount to
     the Administrative Agent, then such amount shall constitute such Lender's
     Loan, included in the applicable Borrowing. If such Lender does not pay
     such amount forthwith upon the Administrative Agent's demand therefor, the
     Administrative Agent may make a demand therefor upon the Borrower, and the
     Borrower shall pay such amount to the Administrative Agent, together with
     interest thereon for the Compensation Period at a rate per annum equal to
     the rate of interest applicable to the applicable Borrowing. Nothing herein
     shall be deemed to relieve any Lender from its obligation to fulfill its
     Commitment or to prejudice any rights which the Administrative Agent or the
     Borrower may have against any Lender as a result of any default by such
     Lender hereunder.

     A notice of the Administrative Agent to any Lender with respect to any
amount owing under this subsection (e) shall be conclusive, absent manifest
error.

     (f) If any Lender makes available to the Administrative Agent funds for any
Loan to be made by such Lender as provided in the foregoing provisions of this
ARTICLE II, and the conditions to the applicable Borrowing set forth in ARTICLE
IV are not satisfied or waived in accordance with the terms hereof, the
Administrative Agent shall return such funds (in like funds as received from
such Lender) to such Lender, without interest.

     (g)   The obligations of the Lenders hereunder to make Loans are several
and not joint. The failure of any Lender to make any Loan on any date required
hereunder shall not relieve any other Lender

                                       31
<Page>

of its corresponding obligation to do so on such date, and no Lender shall be
responsible for the failure of any other Lender to so make its Loan or purchase
its participation.

     (h) Nothing herein shall be deemed to obligate any Lender to obtain the
funds for any Loan in any particular place or manner or to constitute a
representation by any Lender that it has obtained or will obtain the funds for
any Loan in any particular place or manner.

     2.12 SHARING OF PAYMENTS. If, other than as expressly provided elsewhere
herein, any Lender shall obtain on account of the Loans made by it, or the
participations in the L/C Obligations, any payment (whether voluntary,
involuntary, through the exercise of any right of set-off, or otherwise) in
excess of its ratable share (or other share contemplated hereunder) thereof,
such Lender shall immediately (a) notify the Administrative Agent of such fact,
and (b) purchase from the other Lenders such participations in the Loans made by
them, and/or such subparticipations in the participations in L/C Obligations
held by them as shall be necessary to cause such purchasing Lender to share the
excess payment in respect of such Loan or such participations, as the case may
be, pro rata with each of them; PROVIDED, HOWEVER, that if all or any portion of
such excess payment is thereafter recovered from the purchasing Lender, such
purchase shall to that extent be rescinded and each other Lender shall repay to
the purchasing Lender the purchase price paid therefor, together with an amount
equal to such paying Lender's ratable share (according to the proportion of (i)
the amount of such paying Lender's required repayment to (ii) the total amount
so recovered from the purchasing Lender) of any interest or other amount paid or
payable by the purchasing Lender in respect of the total amount so recovered.
The Borrower agrees that any Lender so purchasing a participation from another
Lender may, to the fullest extent permitted by law, exercise all its rights of
payment (including the right of set-off, but subject to SECTION 10.09) with
respect to such participation as fully as if such Lender were the direct
creditor of the Borrower in the amount of such participation. The Administrative
Agent will keep records (which shall be conclusive and binding in the absence of
manifest error) of participations purchased under this Section and will in each
case notify the Lenders following any such purchases or repayments. Each Lender
that purchases a participation pursuant to this Section shall from and after
such purchase have the right to give all notices, requests, demands, directions
and other communications under this Agreement with respect to the portion of the
Obligations purchased to the same extent as though the purchasing Lender were
the original owner of the Obligations purchased.

     2.13 PRIORITY OF HEDGING OBLIGATIONS. Any amounts received in satisfaction
of any Obligations arising under the Loan Documents, including, without
limitation, Obligations under this Agreement and any Lender Hedging Agreement,
shall rank PARI PASSU in right of payment and shall be used to repay such
Obligations on a pro rata basis.

     2.14  LETTERS OF CREDIT. (a) THE LETTER OF CREDIT COMMITMENT.

           (i) Subject to the terms and conditions set forth herein, (A) the L/C
     Issuer agrees, in reliance upon the agreements of the other Lenders set
     forth in this SECTION 2.14, (1) from time to time on any Business Day
     during the period from the Conditions Effective Date until the Letter of
     Credit Expiration Date, to issue Letters of Credit for the account of the
     Borrower or its Subsidiaries, and to amend or renew Letters of Credit
     previously issued by it, in accordance with subsection (b) below, and (2)
     to honor drafts under the Letters of Credit; and (B) the Lenders severally
     agree to participate in Letters of Credit issued for the account of the
     Borrower and its Subsidiaries; PROVIDED that the L/C Issuer shall not be
     obligated to make any L/C Credit Extension with respect to any Letter of
     Credit, and no Lender shall be obligated to participate in, any Letter of
     Credit if as of the date of such L/C Credit Extension, (x) the Outstanding
     Amount of all L/C Obligations and all Loans would exceed the Aggregate
     Commitments, (y) the aggregate Outstanding Amount of the Loans of any
     Lender, PLUS such Lender's Pro Rata Share of the

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     Outstanding Amount of all L/C Obligations would exceed such Lender's
     Commitment, or (z) the Outstanding Amount of the L/C Obligations would
     exceed the Letter of Credit Sublimit. Within the foregoing limits, and
     subject to the terms and conditions hereof, the Borrower's ability to
     obtain Letters of Credit shall be fully revolving, and accordingly the
     Borrower may, during the foregoing period, obtain Letters of Credit to
     replace Letters of Credit that have expired or that have been drawn upon
     and reimbursed.

           (ii) The L/C Issuer shall be under no obligation to issue any Letter
     of Credit if:

                 (A) any order, judgment or decree of any Governmental Authority
           or arbitrator shall by its terms purport to enjoin or restrain the
           L/C Issuer from issuing such Letter of Credit, or any Law applicable
           to the L/C Issuer or any request or directive (whether or not having
           the force of law) from any Governmental Authority with jurisdiction
           over the L/C Issuer shall prohibit, or request that the L/C Issuer
           refrain from, the issuance of letters of credit generally or such
           Letter of Credit in particular or shall impose upon the L/C Issuer
           with respect to such Letter of Credit any restriction, reserve or
           capital requirement (for which the L/C Issuer is not otherwise
           compensated hereunder) not in effect on the Closing Date, or shall
           impose upon the L/C Issuer any unreimbursed loss, cost or expense
           which was not applicable on the Closing Date and which the L/C Issuer
           in good faith deems material to it;

                 (B) subject to SECTION 2.14(b)(iii), the expiry date of such
           requested Letter of Credit would occur more than twelve months after
           the date of issuance or last renewal, unless the Required Lenders
           have approved such expiry date;

                 (C) the expiry date of such requested Letter of Credit would
           occur after the Letter of Credit Expiration Date, unless all the
           Lenders have approved such expiry date;

                 (D) the issuance of such Letter of Credit would violate one or
           more policies of the L/C Issuer generally applicable to all
           borrowers; or

                 (E) such Letter of Credit is in a face amount less than
           $100,000, or is to be used for a purpose other than as described in
           SECTION 6.12 or is denominated in a currency other than Dollars.

           (iii) The L/C Issuer shall be under no obligation to amend any Letter
     of Credit if (A) the L/C Issuer would have no obligation at such time to
     issue such Letter of Credit in its amended form under the terms hereof, or
     (B) the beneficiary of such Letter of Credit does not accept the proposed
     amendment to such Letter of Credit.

     (b)   Procedures for Issuance and Amendment of Letters of Credit; Evergreen
Letters of Credit.

           (i) Each Letter of Credit shall be issued or amended, as the case may
     be, upon the request of the Borrower delivered to the L/C Issuer (with a
     copy to the Administrative Agent) in the form of a Letter of Credit
     Application, appropriately completed and signed by a Responsible Officer of
     the Borrower. Such L/C Application must be received by the L/C Issuer and
     the Administrative Agent not later than 11:00 a.m., New York time, at least
     two Business Days (or such later date and time as the L/C Issuer may agree
     in a particular instance in its sole discretion) prior to the proposed
     issuance date or date of amendment, as the case may be. In the case of a

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     request for an initial issuance of a Letter of Credit, such Letter of
     Credit Application shall specify in form and detail satisfactory to the L/C
     Issuer: (A) the proposed issuance date of the requested Letter of Credit
     (which shall be a Business Day); (B) the amount thereof; (C) the expiry
     date thereof; (D) the name and address of the beneficiary thereof; (E) the
     documents to be presented by such beneficiary in case of any drawing
     thereunder; (F) the full text of any certificate to be presented by such
     beneficiary in case of any drawing thereunder; and (G) such other matters
     as the L/C Issuer may require. In the case of a request for an amendment of
     any outstanding Letter of Credit, such Letter of Credit Application shall
     specify in form and detail satisfactory to the L/C Issuer (A) the Letter of
     Credit to be amended; (B) the proposed date of amendment thereof (which
     shall be a Business Day); (C) the nature of the proposed amendment; and (D)
     such other matters as the L/C Issuer may require.

           (ii) Promptly after receipt of any Letter of Credit Application, the
     L/C Issuer will confirm with the Administrative Agent (by telephone or in
     writing) that the Administrative Agent has received a copy of such Letter
     of Credit Application from the Borrower and, if not, the L/C Issuer will
     provide the Administrative Agent with a copy thereof. Upon receipt by the
     L/C Issuer of confirmation from the Administrative Agent that the requested
     issuance or amendment is permitted in accordance with the terms hereof,
     then, subject to the terms and conditions hereof, the L/C Issuer shall, on
     the requested date, issue a Letter of Credit for the account of the
     Borrower or enter into the applicable amendment, as the case may be, in
     each case in accordance with the L/C Issuer's usual and customary business
     practices. Immediately upon the issuance of each Letter of Credit, each
     Lender shall be deemed to, and hereby irrevocably and unconditionally
     agrees to, purchase from the L/C Issuer a participation in such Letter of
     Credit in an amount equal to the product of such Lender's Pro Rata Share
     TIMES the amount of such Letter of Credit.

           (iii) If the Borrower so requests in any applicable Letter of Credit
     Application, the L/C Issuer may, in it sole and absolute discretion, agree
     to issue a Letter of Credit that has automatic renewal provisions (each, an
     "EVERGREEN LETTER OF CREDIT"); PROVIDED that any such Evergreen Letter of
     Credit must permit the L/C Issuer to prevent any such renewal at least once
     in each twelve-month period (commencing with the date of issuance of such
     Letter of Credit) by giving prior notice to the beneficiary thereof not
     later than a day (the "NONRENEWAL NOTICE DATE") in each such twelve-month
     period to be agreed upon at the time such Letter of Credit is issued.
     Unless otherwise directed by the L/C Issuer, the Borrower shall not be
     required to make a specific request to the L/C Issuer for any such renewal.
     Once an Evergreen Letter of Credit has been issued, the Lenders shall be
     deemed to have authorized (but may not require) the L/C Issuer to permit
     the renewal of such Letter of Credit at any time to a date not later than
     the Letter of Credit Expiration Date; PROVIDED, HOWEVER, that the L/C
     Issuer shall not permit any such renewal if it has received notice on or
     before the Business Day immediately preceding the Nonrenewal Notice Date
     (1) from the Administrative Agent that the Required Lenders have elected
     not to permit such renewal or (2) from any Lender stating that one or more
     of the applicable conditions specified in SECTION 4.03 is not then
     satisfied and directing the L/C Issuer not to permit such renewal.
     Notwithstanding anything to the contrary contained herein, the L/C Issuer
     shall have no obligation to permit the renewal of any Evergreen Letter of
     Credit at any time.

           (iv) Promptly after its delivery of any Letter of Credit or any
     amendment to a Letter of Credit to an advising bank with respect thereto or
     to the beneficiary thereof, the L/C Issuer will also deliver to the
     Borrower and the Administrative Agent a true and complete copy of such
     Letter of Credit or amendment.

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<Page>

     (c)   DRAWINGS AND REIMBURSEMENTS; FUNDING OF PARTICIPATIONS.

           (i) Upon any drawing under any Letter of Credit, the L/C Issuer shall
     notify the Borrower and the Administrative Agent thereof. Not later than
     11:00 a.m., New York time, on the date of any payment by the L/C Issuer
     under a Letter of Credit (each such date, an "HONOR DATE"), the Borrower
     shall reimburse the L/C Issuer through the Administrative Agent in an
     amount equal to the amount of such drawing. If the Borrower fails to so
     reimburse the L/C Issuer by such time, the Administrative Agent shall
     promptly notify each Lender of the Honor Date, the amount of the
     unreimbursed drawing (the "UNREIMBURSED AMOUNT"), and such Lender's Pro
     Rata Share thereof. In such event, the Borrower shall be deemed to have
     requested a Borrowing of Base Rate Loans to be disbursed on the Honor Date
     in an amount equal to the Unreimbursed Amount, without regard to the
     minimum and multiples specified in SECTION 2.03 for the principal amount of
     Base Rate Loans, but subject to the amount of the unutilized portion of the
     Aggregate Commitments and the conditions set forth in SECTION 4.03 (other
     than the delivery of a Loan Notice). Any notice given by the L/C Issuer or
     the Administrative Agent pursuant to this SECTION 2.14(c)(i) may be given
     by telephone if immediately confirmed in writing; PROVIDED that the lack of
     such an immediate confirmation shall not affect the conclusiveness or
     binding effect of such notice.

           (ii) Each Lender (including the Lender acting as L/C Issuer) shall
     upon any notice pursuant to SECTION 2.14(c)(i) make funds available to the
     Administrative Agent for the account of the L/C Issuer at the
     Administrative Agent's Office in an amount equal to its Pro Rata Share of
     the Unreimbursed Amount not later than 1:00 p.m., New York time, on the
     Business Day specified in such notice by the Administrative Agent,
     whereupon, subject to the provisions of SECTION 2.14(c)(iii), each Lender
     that so makes funds available shall be deemed to have made a Base Rate Loan
     to the Borrower in such amount. The Administrative Agent shall remit the
     funds so received to the L/C Issuer.

           (iii) With respect to any Unreimbursed Amount that is not fully
     refinanced by a Borrowing of Base Rate Loans because the conditions set
     forth in SECTION 4.03 cannot be satisfied or for any other reason, the
     Borrower shall be deemed to have incurred from the L/C Issuer an L/C
     Borrowing in the amount of the Unreimbursed Amount that is not so
     refinanced, which L/C Borrowing shall be due and payable on demand
     (together with interest) and shall bear interest at the Default Rate. In
     such event, each Lender's payment to the Administrative Agent for the
     account of the L/C Issuer pursuant to SECTION 2.14(c)(ii) shall be deemed
     payment in respect of its participation in such L/C Borrowing and shall
     constitute an L/C Advance from such Lender in satisfaction of its
     participation obligation under this SECTION 2.14.

           (iv) Until each Lender funds its Loan or L/C Advance pursuant to this
     SECTION 2.14(c) to reimburse the L/C Issuer for any amount drawn under any
     Letter of Credit, interest in respect of such Lender's Pro Rata Share of
     such amount shall be solely for the account of the L/C Issuer.

           (v) Each Lender's obligation to make Loans or L/C Advances to
     reimburse the L/C Issuer for amounts drawn under Letters of Credit, as
     contemplated by this SECTION 2.14(c), shall be absolute and unconditional
     and shall not be affected by any circumstance, including (A) any set-off,
     counterclaim, recoupment, defense or other right which such Lender may have
     against the L/C Issuer, the Borrower or any other Person for any reason
     whatsoever; (B) the occurrence or continuance of a Default or Event of
     Default, or (C) any other occurrence, event or condition, whether or not
     similar to any of the foregoing. Any such reimbursement shall not relieve
     or otherwise impair the obligation of the Borrower to reimburse the L/C
     Issuer for the amount of any

                                       35
<Page>

     payment made by the L/C Issuer under any Letter of Credit, together with
     interest as provided herein.

           (vi) If any Lender fails to make available to the Administrative
     Agent for the account of the L/C Issuer any amount required to be paid by
     such Lender pursuant to the foregoing provisions of this SECTION 2.14(c) by
     the time specified in SECTION 2.14(c)(ii), the L/C Issuer shall be entitled
     to recover from such Lender (acting through the Administrative Agent), on
     demand, such amount with interest thereon for the period from the date such
     payment is required to the date on which such payment is immediately
     available to the L/C Issuer at a rate per annum equal to the Federal Funds
     Rate from time to time in effect. A certificate of the L/C Issuer submitted
     to any Lender (through the Administrative Agent) with respect to any
     amounts owing under this clause (vi) shall be conclusive absent manifest
     error.

     (d)   REPAYMENT OF PARTICIPATIONS.

           (i) At any time after the L/C Issuer has made a payment under any
     Letter of Credit and has received from any Lender such Lender's L/C Advance
     in respect of such payment in accordance with SECTION 2.14(c), if the
     Administrative Agent receives for the account of the L/C Issuer any payment
     related to such Letter of Credit (whether directly from the Borrower or
     otherwise, including proceeds of cash Collateral applied thereto by the
     Administrative Agent), or any payment of interest thereon, the
     Administrative Agent will distribute to such Lender its Pro Rata Share
     thereof in the same funds as those received by the Administrative Agent.

           (ii) If any payment received by the Administrative Agent for the
     account of the L/C Issuer pursuant to SECTION 2.14(c)(i) is required to be
     returned, each Lender shall pay to the Administrative Agent for the account
     of the L/C Issuer its Pro Rata Share thereof on demand of the
     Administrative Agent, plus interest thereon from the date of such demand to
     the date such amount is returned by such Lender, at a rate per annum equal
     to the Federal Funds Rate from time to time in effect.

     (e) OBLIGATIONS ABSOLUTE. The obligation of the Borrower to reimburse the
L/C Issuer for each drawing under each Letter of Credit, and to repay each L/C
Borrowing and each drawing under a Letter of Credit that is refinanced by a
Borrowing of Loans, shall be absolute, unconditional and irrevocable, and shall
be paid strictly in accordance with the terms of this Agreement under all
circumstances, including the following:

           (i)   any lack of validity or enforceability of such Letter of
     Credit, this Agreement, or any other agreement or instrument relating
     thereto;

           (ii) the existence of any claim, counterclaim, set-off, defense or
     other right that the Borrower may have at any time against any beneficiary
     or any transferee of such Letter of Credit (or any Person for whom any such
     beneficiary or any such transferee may be acting), the L/C Issuer or any
     other Person, whether in connection with this Agreement, the transactions
     contemplated hereby or by such Letter of Credit or any agreement or
     instrument relating thereto, or any unrelated transaction;

           (iii) any draft, demand, certificate or other document presented
     under such Letter of Credit proving to be forged, fraudulent, invalid or
     insufficient in any respect or any statement therein being untrue or
     inaccurate in any respect; or any loss or delay in the transmission or
     otherwise of any document required in order to make a drawing under such
     Letter of Credit;

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<Page>

           (iv) any payment by the L/C Issuer under such Letter of Credit
     against presentation of a draft or certificate that does not strictly
     comply with the terms of such Letter of Credit; or any payment made by the
     L/C Issuer under such Letter of Credit to any Person purporting to be a
     trustee in bankruptcy, debtor-in-possession, assignee for the benefit of
     creditors, liquidator, receiver or other representative of or successor to
     any beneficiary or any transferee of such Letter of Credit, including any
     arising in connection with any proceeding under any Debtor Relief Law; or

           (v) any other circumstance or happening whatsoever, whether or not
     similar to any of the foregoing, that might otherwise constitute a defense
     available to, or a discharge of, the Borrower.

     The Borrower shall promptly examine a copy of each Letter of Credit and
each amendment thereto that is delivered to it and, in the event of any claim of
noncompliance with the Borrower's instructions or other irregularity, the
Borrower will immediately notify the L/C Issuer. The Borrower shall be
conclusively deemed to have waived any such claim against the L/C Issuer and its
correspondents unless such notice is given as aforesaid.

     (f) ROLE OF L/C ISSUER. Each Lender and the Borrower agree that, in paying
any drawing under a Letter of Credit, the L/C Issuer shall not have any
responsibility to obtain any document (other than any sight draft, certificates
and documents expressly required by the Letter of Credit) or to ascertain or
inquire as to the validity or accuracy of any such document or the authority of
the Person executing or delivering any such document. No Agent-Related Person
nor any of the respective correspondents, participants or assignees of the L/C
Issuer shall be liable to any Lender for (i) any action taken or omitted in
connection herewith at the request or with the approval of the Lenders or the
Required Lenders, as applicable; (ii) any action taken or omitted in the absence
of gross negligence or willful misconduct; or (iii) the due execution,
effectiveness, validity or enforceability of any document or instrument related
to any Letter of Credit or Letter of Credit Application. The Borrower hereby
assumes all risks of the acts or omissions of any beneficiary or transferee with
respect to its use of any Letter of Credit; PROVIDED, HOWEVER, that this
assumption is not intended to, and shall not, preclude the Borrower's pursuing
such rights and remedies as it may have against the beneficiary or transferee at
law or under any other agreement. No Agent-Related Person, nor any of the
respective correspondents, participants or assignees of the L/C Issuer, shall be
liable or responsible for any of the matters described in clauses (i) through
(v) of SECTION 2.14(e); PROVIDED, HOWEVER, that anything in such clauses to the
contrary notwithstanding, the Borrower may have a claim against the L/C Issuer,
and the L/C Issuer may be liable to the Borrower, to the extent, but only to the
extent, of any direct, as opposed to consequential or exemplary, damages
suffered by the Borrower which the Borrower proves were caused by the L/C
Issuer's willful misconduct or gross negligence or the L/C Issuer's willful
failure to pay under any Letter of Credit after the presentation to it by the
beneficiary of a sight draft and certificate(s) strictly complying with the
terms and conditions of a Letter of Credit. In furtherance and not in limitation
of the foregoing, the L/C Issuer may accept documents that appear on their face
to be in order, without responsibility for further investigation, regardless of
any notice or information to the contrary, and the L/C Issuer shall not be
responsible for the validity or sufficiency of any instrument transferring or
assigning or purporting to transfer or assign a Letter of Credit or the rights
or benefits thereunder or proceeds thereof, in whole or in part, which may prove
to be invalid or ineffective for any reason.

     (g)   CASH COLLATERAL. Upon the request of the Administrative Agent, (i) if
the L/C Issuer has honored any full or partial drawing request under any Letter
of Credit and such drawing has resulted in an L/C Borrowing, or (ii) if, as of
the Letter of Credit Expiration Date, any Letter of Credit may for any

                                       37
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reason remain outstanding and partially or wholly undrawn, the Borrower shall
immediately Cash Collateralize the then Outstanding Amount of all L/C
Obligations (in an amount equal to such Outstanding Amount). The Borrower hereby
grants the Administrative Agent, for the benefit of the L/C Issuer and the
Lenders, a Lien on all such cash and deposit accounts at Bank of America.

     (h) APPLICABILITY OF ISP98. Unless otherwise expressly agreed by the L/C
Issuer and the Borrower when a Letter of Credit is issued (including any such
agreement applicable to an Existing Letter of Credit), the rules of the
"International Standby Practices 1998" published by the Institute of
International Banking Law & Practice (or such later version thereof as may be in
effect at the time of issuance) shall apply to each Letter of Credit.

     (i) LETTER OF CREDIT FEES. The Borrower shall pay to the Administrative
Agent for the account of each Lender in accordance with its Pro Rata Share a
Letter of Credit fee for each Letter of Credit issued equal to the Applicable
Rate TIMES the actual daily undrawn amount under each Letter of Credit. Such fee
for each Letter of Credit shall be due and payable on the last Business Day of
each March, June, September and December, commencing with the first such date to
occur after the issuance of such Letter of Credit, and on the Letter of Credit
Expiration Date. If there is any change in the Applicable Rate during any
quarter, the actual daily undrawn amount of each Letter of Credit shall be
computed and multiplied by the Applicable Rate separately for each period during
such quarter that such Applicable Rate was in effect.

     (j) FRONTING FEE AND DOCUMENTARY AND PROCESSING CHARGES PAYABLE TO L/C
ISSUER. The Borrower shall pay directly to the L/C Issuer for its own account a
fronting fee in an amount with respect to each Letter of Credit issued equal to
the greater of (i) $500 or (ii) 1/8 of 1% calculated on the face amount thereof.
In addition, the Borrower shall pay directly to the L/C Issuer for its own
account the customary issuance, presentation, amendment and other processing
fees, and other standard costs and charges, of the L/C Issuer relating to
letters of credit as from time to time in effect. Such fees and charges are due
and payable on demand and are nonrefundable.

     (k)   CONFLICT WITH LETTER OF CREDIT APPLICATION. In the event of any
conflict between the terms hereof and the terms of any Letter of Credit
Application, the terms hereof shall control.

                                  ARTICLE III.
                     TAXES, YIELD PROTECTION AND ILLEGALITY

     3.01  TAXES.

     (a) Any and all payments by the Borrower to or for the account of the
Administrative Agent or any Lender under any Loan Document shall be made free
and clear of and without deduction for any and all present or future taxes,
duties, levies, imposts, deductions, assessments, fees, withholdings or similar
charges, and all liabilities with respect thereto, EXCLUDING, in the case of the
Administrative Agent and each Lender, taxes imposed on or measured by its net
income, and franchise taxes imposed on it (in lieu of net income taxes), by the
jurisdiction (or any political subdivision thereof) under the Laws of which the
Administrative Agent or such Lender, as the case may be, is organized or
maintains its Lending Office (all such non-excluded taxes, duties, levies,
imposts, deductions, assessments, fees, withholdings or similar charges, and
liabilities being hereinafter referred to as "TAXES"). If the Borrower shall be
required by any Laws to deduct any Taxes from or in respect of any sum payable
under any Loan Document to the Administrative Agent or any Lender, (i) the sum
payable shall be increased as necessary so that after making all required
deductions (including deductions applicable to additional sums payable under
this Section), each of the Administrative Agent and such Lender receives an
amount equal to the

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sum it would have received had no such deductions been made, (ii) the Borrower
shall make such deductions, (iii) the Borrower shall pay the full amount
deducted to the relevant taxation authority or other authority in accordance
with applicable Laws, and (iv) within 30 days after the date of such payment,
the Borrower shall furnish to the Administrative Agent (which shall forward the
same to such Lender) the original or a certified copy of a receipt evidencing
payment thereof.

     (b) In addition, the Borrower agrees to pay any and all present or future
stamp, court or documentary taxes and any other excise or property taxes or
charges or similar levies which arise from any payment made under any Loan
Document or from the execution, delivery, performance, enforcement or
registration of, or otherwise with respect to, any Loan Document (hereinafter
referred to as "OTHER TAXES").

     (c) If the Borrower shall be required to deduct or pay any Taxes or Other
Taxes from or in respect of any sum payable under any Loan Document to the
Administrative Agent or any Lender, the Borrower shall also pay to the
Administrative Agent (for the account of such Lender) or to such Lender, at the
time interest is paid, such additional amount that such Lender specifies as
necessary to preserve the after-tax yield (after factoring in all taxes,
including taxes imposed on or measured by net income) such Lender would have
received if such Taxes or Other Taxes had not been imposed.

     (d) The Borrower agrees to indemnify the Administrative Agent and each
Lender for (i) the full amount of Taxes and Other Taxes (including any Taxes or
Other Taxes imposed or asserted by any jurisdiction on amounts payable under
this Section) paid by the Administrative Agent and such Lender, (ii) amounts
payable under SECTION 3.01(c) and (iii) any liability (including penalties,
interest and expenses) arising therefrom or with respect thereto. Payment under
this subsection (d) shall be made within 30 days after the date the Lender or
the Administrative Agent makes a demand therefor.

     3.02 ILLEGALITY. If any Lender determines that any Law has made it
unlawful, or that any Governmental Authority has asserted that it is unlawful,
for any Lender or its applicable Lending Office to make, maintain or fund
Eurodollar Rate Loans, or materially restricts the authority of such Lender to
purchase or sell, or to take deposits of, Dollars in the applicable offshore
Dollar market, or to determine or charge interest rates based upon the
Eurodollar Rate, then, on notice thereof by such Lender to the Borrower through
the Administrative Agent, any obligation of such Lender to make or continue
Eurodollar Rate Loans or to convert Base Rate Loans to Eurodollar Rate Loans
shall be suspended until such Lender notifies the Administrative Agent and the
Borrower that the circumstances giving rise to such determination no longer
exist. Upon receipt of such notice, the Borrower shall, upon demand from such
Lender (with a copy to the Administrative Agent), prepay or, if applicable,
convert all Eurodollar Rate Loans of such Lender to Base Rate Loans, either on
the last day of the Interest Period thereof, if such Lender may lawfully
continue to maintain such Eurodollar Rate Loans to such day, or immediately, if
such Lender may not lawfully continue to maintain such Eurodollar Rate Loans.
Upon any such prepayment or conversion, the Borrower shall also pay interest on
the amount so prepaid or converted. Each Lender agrees to designate a different
Lending Office if such designation will avoid the need for such notice and will
not, in the reasonable judgment of such Lender, otherwise be materially
disadvantageous to such Lender.

     3.03 INABILITY TO DETERMINE RATES. If the Administrative Agent determines
in connection with any request for a Eurodollar Rate Loan or a conversion to or
continuation thereof that (a) Dollar deposits are not being offered to banks in
the applicable offshore Dollar market for the applicable amount and Interest
Period of such Eurodollar Rate Loan, or adequate and reasonable means do not
exist for determining the Eurodollar Rate for such Eurodollar Rate Loan, or (b)
if the Required Lenders determine and notify the Administrative Agent that the
Eurodollar Rate for such Eurodollar Rate Loan does not

                                       39
<Page>

adequately and fairly reflect the cost to the Lenders of funding such Eurodollar
Rate Loan, then the Administrative Agent will promptly notify the Borrower and
all Lenders. Thereafter, the obligation of the Lenders to make or maintain
Eurodollar Rate Loans shall be suspended until the Administrative Agent revokes
such notice. Upon receipt of such notice, the Borrower may revoke any pending
request for a Borrowing, conversion or continuation of Eurodollar Rate Loans or,
failing that, will be deemed to have converted such request into a request for a
Borrowing of Base Rate Loans in the amount specified therein.

     3.04  INCREASED COST AND REDUCED RETURN; CAPITAL ADEQUACY; RESERVES ON
EURODOLLAR RATE LOANS.

     (a) If any Lender determines that as a result of a Change in Law, or such
Lender's compliance therewith, there shall be any increase in the cost to such
Lender of agreeing to make or making, funding or maintaining Eurodollar Rate
Loans, or a reduction in the amount received or receivable by such Lender in
connection with any of the foregoing (excluding for purposes of this subsection
(a) any such increased costs or reduction in amount resulting from (i) Taxes or
Other Taxes (as to which SECTION 3.01 shall govern), (ii) changes in the basis
of taxation of overall net income or overall gross income by the United States
or any foreign jurisdiction or any political subdivision of either thereof under
the Laws of which such Lender is organized or has its Lending Office, and (iii)
reserve requirements contemplated by SECTION 3.04(c) utilized, as to Eurodollar
Rate Loans, in the determination of the Eurodollar Rate), then from time to time
upon demand of such Lender (with a copy of such demand to the Administrative
Agent), the Borrower shall pay to such Lender such additional amounts as will
compensate such Lender for such increased cost or reduction.

     (b) If any Lender determines a Change In Law has the effect of reducing the
rate of return on the capital of such Lender or any corporation controlling such
Lender as a consequence of such Lender's obligations hereunder (taking into
consideration its policies with respect to capital adequacy and such Lender's
desired return on capital), then from time to time upon demand of such Lender
(with a copy of such demand to the Administrative Agent), the Borrower shall pay
to such Lender such additional amounts as will compensate such Lender for such
reduction.

     (c) The Borrower shall pay to each Lender, as long as such Lender shall be
required under regulations of the Board to maintain reserves with respect to
liabilities or assets consisting of or including Eurocurrency funds or deposits
(currently known as "EUROCURRENCY LIABILITIES"), additional costs on the unpaid
principal amount of each Eurodollar Rate Loan equal to the actual costs of such
reserves allocated to such Loan by such Lender (as determined by such Lender in
good faith, which determination shall be conclusive), which shall be due and
payable on each date on which interest is payable on such Loan, PROVIDED the
Borrower shall have received at least 15 days' prior notice (with a copy to the
Administrative Agent) of such additional interest from such Lender. If a Lender
fails to give notice 15 days prior to the relevant Interest Payment Date, such
additional interest shall be due and payable 15 days from receipt of such
notice.

     3.05 FUNDING LOSSES. Upon demand of any Lender (with a copy to the
Administrative Agent) from time to time, the Borrower shall promptly compensate
such Lender for and hold such Lender harmless from any loss, cost or expense
incurred by it as a result of:

     (a) any continuation, conversion, payment or prepayment of any Loan other
than a Base Rate Loan on a day other than the last day of the Interest Period
for such Loan (whether voluntary, mandatory, automatic, by reason of
acceleration, or otherwise); or

                                       40
<Page>

     (b) any failure by the Borrower (for a reason other than the failure of
such Lender to make a Loan) to prepay, borrow, continue or convert any Loan
other than a Base Rate Loan on the date or in the amount notified by the
Borrower; including any loss of anticipated profits and any loss or expense
arising from the liquidation or reemployment of funds obtained by it to maintain
such Loan or from fees payable to terminate the deposits from which such funds
were obtained. The Borrower shall also pay any customary administrative fees
charged by such Lender in connection with the foregoing.

     For purposes of calculating amounts payable by the Borrower to the Lenders
under this SECTION 3.05, each Lender shall be deemed to have funded each
Eurodollar Rate Loan made by it at the Eurodollar Rate for such Loan by a
matching deposit or other borrowing in the applicable offshore Dollar interbank
market for a comparable amount and for a comparable period, whether or not such
Eurodollar Rate Loan was in fact so funded.

     3.06 MATTERS APPLICABLE TO ALL REQUESTS FOR COMPENSATION. A certificate of
the Administrative Agent or any Lender claiming compensation under this ARTICLE
III and setting forth the additional amount or amounts to be paid to it
hereunder shall be conclusive in the absence of manifest error. In determining
such amount, the Administrative Agent or such Lender may use any reasonable
averaging and attribution methods.

     3.07 SURVIVAL. All of the Borrower's obligations under this ARTICLE III
shall survive termination of the Commitments and payment in full of all the
other Obligations.

                                   ARTICLE IV.
                       CONDITIONS PRECEDENT TO BORROWINGS

     4.01  CONDITIONS TO INITIAL CREDIT EXTENSION. The obligation of each Lender
to fund its portion of the initial Credit Extension hereunder is subject to
satisfaction of the following conditions precedent:

     (a) The Administrative Agent's receipt of the following, each of which
shall be originals or facsimiles (followed promptly by originals) and unless
otherwise specified, each properly executed by an authorized officer of the
signing Loan Party, each dated the Conditions Effective Date (or, in the case of
certificates of governmental officials, a recent date before the Conditions
Effective Date) or the Closing Date, as appropriate, and each in form and
substance satisfactory to the Administrative Agent and its legal counsel:

           (i) executed counterparts of this Agreement, the Agreement Regarding
     Collateral, the Guaranties, and all other Collateral Documents each dated
     as of the Closing Date or as of the Conditions Effective Date;

           (ii) Notes executed by the Borrower in favor of each Lender
     requesting such Notes, each in a principal amount equal to such Lender's
     Committed Sum, each dated as of the Closing Date or as of the Conditions
     Effective Date;

           (iii) such certificates of resolutions or other action, incumbency
     certificates and/or other certificates of officers of each Loan Party as
     the Administrative Agent may require to establish the identities of and
     verify the authority and capacity of each officer thereof authorized to act
     in connection with this Agreement and the other Loan Documents to which
     such Loan Party is a party;

                                       41
<Page>

           (iv) such evidence as the Administrative Agent may reasonably require
     to verify that each Loan Party is duly organized or formed, validly
     existing, and in good standing in the jurisdiction of its organization;

           (v) a certificate signed by a Responsible Officer of the Borrower
     certifying (A) that the MLP Offering Closing has occurred and that the
     gross proceeds of the sale of limited partner units (other than proceeds
     paid by the General Partner and MarkWest Parties) are not less than
     $36,000,000, (B) that the representations and warranties contained in
     ARTICLE V are true and correct in all respects on and as of such date, (C)
     that no Default or Event of Default has occurred and is continuing as of
     such date, (D) since December 31, 2001 there has occurred no material
     adverse change in (x) the business, assets, liabilities (actual or
     contingent), operations, or condition (financial or otherwise) or prospects
     of the Borrower or any Guarantor, or (y) any of the businesses, assets or
     liabilities acquired or assumed or being acquired or assumed by the
     Borrower or any of its Subsidiaries, (E) that the Purchased Assets have
     been conveyed to the Borrower pursuant to the Contribution Agreement, and
     the Borrower and its Subsidiaries own the assets and businesses reflected
     on the MLP Balance Sheet free and clear of all Liens other than Permitted
     Liens, (F) there is no litigation, investigation or proceeding known to and
     affecting the Borrower or any Borrower Affiliate for which the Borrower is
     required to give notice pursuant to SECTION 6.03(c) (or, if there is any
     such litigation, investigation or proceeding, then a notice containing the
     information required by SECTION 6.03(c) shall be given concurrently with
     the delivery of the certificate given pursuant to this clause (v)), and (G)
     no action, suit, investigation or proceeding is pending or threatened in
     any court or before any arbitrator or governmental authority by or against
     the Borrower, any Guarantor, the General Partner, or any of their
     respective properties, that (x) could reasonably be expected to materially
     and adversely affect the Borrower or any Guarantor, or (y) seeks to affect
     or pertains to any transaction contemplated hereby or the ability of the
     Borrower or any Guarantor to perform its obligations under the Loan
     Documents;

           (vi) a certificate of a Responsible Officer (A) listing the Material
     Agreements and the Parent Material Agreements then in effect (which shall
     include those agreements set forth in CLAUSES (a), (b), (c), and (d) of the
     definition of Material Agreements and those agreements set forth in CLAUSES
     (a), (b), (c), and (d) of the definition of Parent Material Agreements),
     each of which shall be in form and substance satisfactory to the Required
     Lenders, and (B) attaching a copy of each of the listed Material Agreements
     and Parent Material Agreements, and (C) certifying that each such Material
     Agreement has been duly executed and is in full force and effect and each
     such Parent Material Agreement has been duly executed by the MarkWest
     Parties party thereto and is in full force and effect;

           (vii) a certificate of a Responsible Officer providing copies of the
     following or a copy of the MLP Registration Statement containing the
     following (A) audited opening balance sheet for each of the MLP and the
     General Partner and unaudited opening balance sheet for the Borrower; (B)
     historical audited financial information for predecessor entities and/or
     businesses for the three (3) years ended December 31, 2001 as set forth in
     the MLP Registration Statement; and (C) such other financial information as
     the Administrative Agent may request.

           (viii) opinions from (A) Baker Botts, L.L.P., counsel to each Loan
     Party and the General Partner, substantially in the form of EXHIBIT F-3
     hereto, (B) Davis Graham & Stubbs LLP, counsel to each Loan Party,
     substantially in the form of EXHIBIT F-1 hereto, (C) Barry Spector, counsel
     to each Loan Party, substantially in the form of EXHIBIT F-2 hereto, and
     (D)

                                       42
<Page>

     local counsel to each Loan Party with respect to each deed of trust or
     mortgage executed by a Loan Party;

           (ix)    a letter from CT Corporation System, Inc., to accept service
     of process in the State of Texas on behalf of the Borrower and each
     Guarantor;

           (x) Receipt of evidence that (a) required approvals have been
     obtained from the lenders under the Parent Credit Agreement and Canadian
     Credit Agreement, and (b) a certificate of MarkWest Parent stating that no
     Default or Event of Default exists under the Parent Credit Agreement or the
     Canadian Credit Agreement or will exist immediately after the closing of
     the MLP Offering and the initial funding of Loans under this Agreement as
     such credit agreements are amended and restated on the Conditions Effective
     Date; and

           (xi) such other assurances, certificates, documents, consents or
     opinions as the Administrative Agent, the L/C Issuer, or the Required
     Lenders reasonably may require.

     (b) Any fees due and payable at the Conditions Effective Date shall have
been paid.

     (c) The Borrower shall have paid Attorney Costs of the Administrative Agent
to the extent invoiced prior to, or on, the Conditions Effective Date.

     (d) The Borrower shall be a direct wholly-owned subsidiary of the MLP, and
MarkWest Parent shall own at least 51% of the General Partner.

     (e) Documents, executed by each Company that has assets or conducts
business, in appropriate form for recording, where necessary, together with:

           (i) such Lien searches as the Administrative Agent shall have
     requested, and such termination statements or other documents as may be
     necessary to confirm that the Collateral is subject to no other Liens
     (other than Permitted Liens) in favor of any Persons;

           (ii) funds sufficient to pay any filing or recording tax or fee in
     connection with any and all UCC-1 financing statements or UCC-3 amendment
     financing statements, or fees associated with the filing of the Mortgages
     or amendments to Mortgages;

           (iii) evidence that the Administrative Agent has been named as loss
     payee under all policies of casualty insurance pertaining to the
     Collateral;

           (iv) such consents, estoppels, subordination agreements and other
     documents and instruments executed by landlords and other Persons party to
     material contracts relating to any Collateral as to which the
     Administrative Agent shall be granted a Lien for the benefit of the
     Lenders, as requested by the Administrative Agent or any Lender;

           (v) certificates evidencing all of the issued and outstanding shares
     of capital stock, partnership interests, or membership interests pledged
     pursuant thereto, which certificates shall in each case be accompanied by
     undated stock powers duly executed in blank, or, if any securities pledged
     pursuant thereto are uncertificated securities, confirmation and evidence
     satisfactory to the Administrative Agent that the security interest in such
     uncertificated securities has been transferred to and perfected by the
     Administrative Agent for the benefit of the Lenders in accordance with the
     Uniform Commercial Code; and

                                       43
<Page>

           (vi) evidence that all other actions necessary or, in the opinion of
     the Administrative Agent or the Lenders, desirable to perfect and protect
     the first priority Lien created by the Collateral Documents (except to the
     extent otherwise permitted hereunder), and to enhance the Administrative
     Agent's ability to preserve and protect its interests in and access to the
     Collateral, have been taken;

     The Administrative Agent shall notify the Borrower and the Lenders of the
Conditions Effective Date, and such notice shall be conclusive and binding.

     4.02 DEADLINE FOR CONDITIONS EFFECTIVE DATE. If for any reason the
Conditions Effective Date has not occurred on or before the 45th day after the
Closing Date, then, unless otherwise agreed by all Lenders, the Aggregate
Commitments shall terminate on and as of such date.

     4.03 CONDITIONS TO ALL LOANS AND L/C CREDIT EXTENSION. The obligation of
each Lender to honor any Borrowing Notice and the obligation of the Issuing Bank
to issue any Letter of Credit is subject to the following conditions precedent:

     (a) The representations and warranties of the Loan Parties contained in
ARTICLE V, or which are contained in any document furnished at any time under or
in connection herewith, including, but not limited to the Collateral Documents,
shall be true and correct on and as of the date of such Loan is made, continued
or converted, as applicable, or such Letter of Credit is issued except to the
extent that such representations and warranties specifically refer to an earlier
date, in which case they shall be true and correct as of such earlier date.

     (b) No Default or Event of Default shall exist or would result from such
proposed Loan, continuation or conversion, or L/C Credit Extension.

     (c) The Administrative Agent and, if applicable, the L/C Issuer, shall have
received a Request for Credit Extension and, if applicable, a Letter of Credit
Application in accordance with the requirements hereof.

     (d) The Administrative Agent shall have received, in form and substance
reasonably satisfactory to it, such other assurances, certificates, documents or
consents related to the foregoing as the Administrative Agent or the Required
Lenders reasonably may require.

     Each Request for Credit Extension submitted by the Borrower shall be deemed
to be a representation and warranty that the conditions specified in SECTIONS
4.03(a) and (b) have been satisfied on and as of the date of the applicable
Credit Extension.

                                   ARTICLE V.
                         REPRESENTATIONS AND WARRANTIES

     Each of the Borrower and the MLP, and each Guarantor by its execution of a
Guaranty, represents and warrants to the Administrative Agent and the Lenders
that:

     5.01 EXISTENCE; QUALIFICATION AND POWER; COMPLIANCE WITH LAWS. As of the
Conditions Effective Date, the Borrower is a direct wholly-owned subsidiary of
the MLP and MarkWest Parent owns at least 51% of the General Partner. The
General Partner and each Loan Party (a) is a corporation, partnership or limited
liability company duly organized or formed, validly existing and in good
standing

                                       44
<Page>

under the Laws of the jurisdiction of its incorporation or organization, (b) has
all requisite power and authority and all governmental licenses, authorizations,
consents and approvals to own its assets, carry on its business and to execute,
deliver, and perform its obligations under the Loan Documents to which it is a
party, (c) is duly qualified and is licensed and in good standing under the Laws
of each jurisdiction where its ownership, lease or operation of properties or
the conduct of its business requires such qualification or license, and (d) is
in compliance with all Laws, except in each case referred to in clause (c) or
this clause (d), to the extent that failure to do so could not reasonably be
expected to have a Material Adverse Effect.

     5.02 AUTHORIZATION; NO CONTRAVENTION. The execution, delivery and
performance by each Loan Party of each Loan Document to which such Person is
party, have been duly authorized by all necessary corporate or other
organizational action, and do not and will not (a) contravene the terms of any
of such Person's Organization Documents; (b) conflict with or result in any
breach or contravention of, or the creation of any Lien under, any material
Contractual Obligation to which such Person is a party or any order, injunction,
writ or decree of any Governmental Authority to which such Person or its
property is subject; or (c) violate any Law.

     5.03 GOVERNMENTAL AUTHORIZATION. No approval, consent, exemption,
authorization, or other action by, or notice to, or filing with, any
Governmental Authority, except for the filings of mortgages and lien notices in
connection with the granting of security interests pursuant to the Collateral
Documents, is necessary or required in connection with the execution, delivery
or performance by, or enforcement against, any Loan Party of this Agreement or
any other Loan Document.

     5.04 BINDING EFFECT. This Agreement has been, and each other Loan Document,
when delivered hereunder, will have been duly executed and delivered by each
Loan Party that is party thereto. This Agreement constitutes, and each other
Loan Document when so delivered will constitute, a legal, valid and binding
obligation of such Loan Party, enforceable against each Loan Party that is party
thereto in accordance with its terms.

     5.05  FINANCIAL STATEMENTS; NO MATERIAL ADVERSE EFFECT.

     (a) The Initial Financial Statements were prepared in accordance with GAAP
consistently applied throughout the period covered thereby, except as otherwise
expressly noted therein. The Initial Financial Statements (i) fairly present the
financial condition of the entities therein named and their respective
Subsidiaries as of the date thereof and their results of operations for the
period covered thereby in accordance in all material respects with GAAP
consistently applied throughout the period covered thereby, except as otherwise
expressly noted therein; and (ii) show all material indebtedness and other
liabilities, direct or contingent, of the entities therein named and their
Subsidiaries as of the date thereof, including liabilities for taxes, material
commitments and Indebtedness in accordance with GAAP consistently applied
throughout the period covered thereby.

     (b) Since December 31, 2001, there has been no event or circumstance that
has or could reasonably be expected to have a Material Adverse Effect.

     5.06 LITIGATION. There are no actions, suits, proceedings, claims or
disputes pending or, to the knowledge of the MLP or the Borrower threatened or
contemplated in writing, at law, in equity, in arbitration or before any
Governmental Authority, by or against the Borrower or any Borrower Affiliate or
against any of their properties or revenues which (a) seek to affect or pertain
to this Agreement or any other Loan Document, the borrowing of Loans, the use of
the proceeds thereof, or the issuance of Letters of Credit hereunder, or (b) if
determined adversely, could reasonably be expected to have a Material Adverse
Effect.

                                       45
<Page>

     5.07 NO DEFAULT. Neither the Borrower nor any Borrower Affiliate is in
default under or with respect to any Contractual Obligation which could be
reasonably expected to have a Material Adverse Effect. No Default or Event of
Default has occurred and is continuing or would result from the consummation of
the transactions contemplated by this Agreement or any other Loan Document.
There is no default under any Material Agreement.

     5.08 OWNERSHIP OF PROPERTY; LIENS. From and after the Conditions Effective
Date, (a) each Loan Party and its Subsidiaries have good title to, or valid
leasehold interests in, all its real and personal property necessary or used in
the ordinary conduct of its business, except for such defects in title as would
not, individually or in the aggregate, have a Material Adverse Effect, and (b)
the property of the MLP, the Borrower and their respective Subsidiaries is
subject to no Liens, other than Permitted Liens.

     5.09 ENVIRONMENTAL COMPLIANCE. The MLP and the Borrower have reasonably
concluded that (a) there are no claims alleging potential liability under or
responsibility for violation of any Environmental Law except any such claims
that could not, individually or in the aggregate, reasonably be expected to have
a Material Adverse Effect, (b) there is no environmental condition or
circumstance, such as the presence or Release of any Hazardous Substance, on any
property owned, operated or used the Borrower or any Borrower Affiliate that
could reasonably be expected to have a Material Adverse Effect, and (c) there is
no violation of or by the Borrower or any Borrower Affiliate of any
Environmental Law, except for such violations as could not, individually or in
the aggregate, reasonably be expected to have a Material Adverse Effect.

     5.10 INSURANCE. The properties of the Borrower and the Borrower Affiliates
are insured with financially sound and reputable insurance companies not
Affiliates of the Borrower, in such amounts, with such deductibles and covering
such risks as are customarily carried by companies engaged in similar businesses
and owning similar properties in localities where the Borrower or the Borrower
Affiliates operate.

     5.11 TAXES. The Borrower and the Borrower Affiliates have filed all
federal, state and other material tax returns and reports required to be filed,
and have paid all federal, state and other material taxes, assessments, fees and
other governmental charges levied or imposed upon them or their properties,
income or assets otherwise due and payable, except those which are being
contested in good faith by appropriate proceedings and for which adequate
reserves have been provided in accordance with GAAP. There is no proposed tax
assessment against any Borrower Affiliate or any of their respective
Subsidiaries that would, if made, have a Material Adverse Effect.

     5.12  ERISA COMPLIANCE. The representations and warranties set forth in
this SECTION 5.12 shall apply only if the Borrower or an ERISA Affiliate
establishes a Plan.

     (a) Each Plan is in compliance in all material respects with the applicable
provisions of ERISA, the Code and other federal or state Laws except to the
extent that noncompliance could not reasonably be expected to have a Material
Adverse Effect. Each Plan that is intended to qualify under SECTION 401(a) of
the Code has received a favorable determination letter from the IRS or an
application for such a letter is currently being processed by the IRS with
respect thereto and, to the best knowledge of the MLP and the Borrower, nothing
has occurred which would prevent, or cause the loss of, such qualification,
except to the extent that nonqualification could not reasonably be expected to
have a Material Adverse Effect. The Borrower and each ERISA Affiliate have made
all required contributions to each Plan subject to SECTION 412 of the Code, and
no application for a funding waiver or an extension of

                                       46
<Page>

any amortization period pursuant to SECTION 412 of the Code has been made with
respect to any Plan, except to the extent that nonpayment could not reasonably
be expected to have a Material Adverse Effect.

     (b) There are no pending or, to the best knowledge of the MLP or the
Borrower, threatened claims, actions or lawsuits, or action by any Governmental
Authority, with respect to any Plan that could reasonably be expected to have a
Material Adverse Effect. Neither the MLP nor the Borrower nor any ERISA
Affiliate has engaged in or knowingly permitted to occur and, to the Borrower's
and the MLP's knowledge, no other party has engaged in or permitted to occur any
prohibited transaction or violation of the fiduciary responsibility rules with
respect to any Plan that has resulted or could reasonably be expected to result
in a Material Adverse Effect.

     (c) (i) No ERISA Event has occurred or is reasonably expected to occur that
could reasonably be expected to have a Material Adverse Effect; (ii) no Pension
Plan has any Unfunded Pension Liability that (when aggregated with any other
Unfunded Pension Liability) has resulted or could reasonably be expected to
result in a Material Adverse Effect; and (iii) neither the Borrower nor any
ERISA Affiliate has engaged in a transaction that could be subject to SECTIONS
4069 or 4212(c) of ERISA that could reasonably be expected to have a Material
Adverse Effect.

     5.13 SUBSIDIARIES AND OTHER INVESTMENTS. As of the Conditions Effective
Date the Borrower will have no Subsidiaries other than those specifically
disclosed in SCHEDULE 5.13, and will have no equity investment in any other
corporation or other entity other than those specifically disclosed in SCHEDULE
5.13. From and after the Conditions Effective Date the MLP has no Subsidiaries
other than the Borrower and the Borrower's Subsidiaries.

     5.14  MARGIN REGULATIONS; INVESTMENT COMPANY ACT; PUBLIC UTILITY HOLDING
COMPANY ACT; USE OF PROCEEDS.

     (a) Neither the Borrower nor any Borrower Affiliate is engaged nor will it
engage, principally or as one of its important activities, in the business of
purchasing or carrying margin stock (within the meaning of Regulation U issued
by the Board), or extending credit for the purpose of purchasing or carrying
margin stock. Margin Stock constitutes less than 25% of those assets of each
Loan Party which are subject to any limitation on a sale, pledge, or other
restrictions hereunder.

     (b) Neither the Borrower nor any Borrower Affiliate, no Person controlling
the Borrower or any Borrower Affiliate, or any Subsidiary thereof (i) is a
"HOLDING COMPANY," or a "SUBSIDIARY COMPANY" of a "HOLDING COMPANY," or an
"AFFILIATE" of a "HOLDING COMPANY" or of a "SUBSIDIARY COMPANY" of a "HOLDING
COMPANY," within the meaning of the Public Utility Holding Company Act of 1935,
or (ii) is or is required to be registered as an "INVESTMENT COMPANY" under the
Investment Company Act of 1940.

     (c) The Borrower will use all proceeds of Credit Extension in the manner
set forth in SECTION 6.12.

     5.15 DISCLOSURE. All material factual information hereto furnished by or on
behalf of the Borrower in writing to the Administrative Agent or any Lender for
purposes of or in connection with this Agreement or any transaction contemplated
hereby, as modified or supplemented by other information so furnished, is true
and accurate in all material respects, and such information is not, or shall not
be, as the case may be, incomplete by omitting to state any material fact
necessary to make such information not misleading. All estimates and projections
delivered to the Administrative Agent or any Lender were based upon information
that was available at the time such estimates or projections were prepared and

                                       47
<Page>

believed to be correct and upon assumptions believed to be reasonable; however,
the Borrower does not warrant that such estimates and projections will
ultimately prove to have been accurate.

     5.16 LABOR MATTERS. To the Borrower's and the MLP's knowledge, there are no
actual or threatened strikes, labor disputes, slowdowns, walkouts, or other
concerted interruptions of operations that could reasonably be expected to have
a Material Adverse Effect.

     5.17 COMPLIANCE WITH LAWS. Neither the Borrower nor any Borrower Affiliate
is in violation of any Laws, OTHER THAN such violations which could not,
individually or collectively, reasonably be expected to have a Material Adverse
Effect. Neither the Borrower nor any Borrower Affiliate has received notice
alleging any noncompliance with any Laws, EXCEPT for such noncompliance which no
longer exists, or which non-compliance could not reasonably be expected to have
a Material Adverse Effect.

     5.18 THIRD PARTY APPROVALS. No approval, consent, exemption, authorization,
or other action by, or notice to, or filing with, any party that is not a party
to this Agreement is necessary or required in connection with the execution,
delivery or performance by, or enforcement against, any Loan Party of this
Agreement or any other Loan Document EXCEPT where obtained or where the failure
to receive such approval, consent, exemption, authorization, or the failure to
do such other action by, or provide such notice could not reasonably be expected
to have a Material Adverse Effect and provided, however, that the transfer of
rights in certain Collateral consisting of rights under contracts to a
foreclosure purchaser may, in some instances, require the consent of third
parties who have rights in such Collateral.

     5.19  SOLVENCY. Neither the Borrower and its Subsidiaries on a consolidated
basis nor the MLP and its Subsidiaries on a consolidated basis are "insolvent"
as such term is used and defined in (i) the United States Bankruptcy Code or
(ii) the Texas Uniform Fraudulent Transfer Act, Tex. Bus. & Com. Code
Ann. Section 24.003.

     5.20 COLLATERAL. (a) The provisions of each of the Collateral Documents are
effective to create in favor of the Administrative Agent for the benefit of the
Lenders, a legal, valid and enforceable first priority security interest in all
right, title and interest of each Company in the Collateral described therein,
except as otherwise permitted hereunder; and financing statements have been
filed in the offices in all of the jurisdictions listed in the schedule to all
Security Agreements and Mortgages.

     (b) All representations and warranties of each Loan Party thereto contained
in the Collateral Documents are true and correct in all material respects.

     (c) None of the terms or provisions of any indenture, mortgage, deed of
trust, agreement or other instrument to which the Borrower or any Borrower
Affiliate is a party or by which the Borrower or any Borrower Affiliate or the
property of the Borrower or any Borrower Affiliate is bound prohibit the filing
or recordation of any of the Loan Documents or any other action which is
necessary or appropriate in connection with the perfection of the Liens on
material assets evidenced and created by any of the Loan Documents.

                                  ARTICLE VI.
                              AFFIRMATIVE COVENANTS

     So long as any Lender shall have any Commitment hereunder, or any Loan or
other Obligation shall remain unpaid or unsatisfied, or any Letter of Credit
shall remain outstanding, each of the Borrower and the MLP shall, and shall
cause each of their Subsidiaries to:

                                       48
<Page>

     6.01  FINANCIAL STATEMENTS. Deliver to the Administrative Agent and each
Lender, in form and detail reasonably satisfactory to the Administrative Agent
and the Required Lenders:

     (a) within 90 days of the date of the MLP Offering Closing, a consolidated
unaudited balance sheet of the MLP and its Subsidiaries as of the MLP Offering
Closing, in reasonable detail and certified by a Responsible Officer of the MLP
as fairly presenting the financial condition of the MLP and its Subsidiaries;

     (b) as soon as available, but in any event within 90 days after the end of
each fiscal year of the MLP, consolidated balance sheets of the MLP and its
Subsidiaries as at the end of such fiscal year, and the related statements of
income and cash flows for such fiscal year, setting forth in each case in
comparative form the figures for the previous fiscal year of the MLP, if any,
all in reasonable detail, audited and accompanied by a report and opinion of
PriceWaterhouseCoopers LLP or other independent certified public accountant of
nationally recognized standing reasonably acceptable to the Required Lenders,
which report and opinion shall be prepared in accordance with GAAP and shall not
be subject to any qualifications or exceptions as to the scope of the audit nor
to any qualifications and exceptions not reasonably acceptable to the Required
Lenders;

     (c) as soon as available, but in any event within 90 days after the end of
each fiscal year of the MLP (which shall be the same as the fiscal year of the
Borrower), an unaudited consolidated balance sheet of the Borrower and its
Subsidiaries as at the end of such fiscal year setting forth in each case in
comparative form the figures for the previous fiscal year for the Borrower, if
any, all in reasonable detail, and the related statements of income and cash
flows for such fiscal year, setting forth in each case in comparative form the
figures for the corresponding fiscal year certified by a Responsible Officer of
the Borrower as fairly presenting the financial condition, results of operations
and cash flows of the Borrower and its Subsidiaries in accordance with GAAP; and

     (d) as soon as available, but in any event within 45 days after the end of
each of the first three fiscal quarters of each fiscal year of the MLP, an
unaudited consolidated balance sheet of the MLP and its Subsidiaries and the
Borrower and its Subsidiaries as at the end of such fiscal quarter, and the
related statements of income and cash flows for such fiscal quarter and for the
portion of the MLP's fiscal year then ended, setting forth in each case in
comparative form the figures for the corresponding fiscal quarter of the
previous fiscal year of the MLP or the Borrower, if any, and the corresponding
portion of the previous fiscal year of the MLP or the Borrower, if any, all in
reasonable detail and certified by a Responsible Officer of the MLP or the
Borrower, as applicable, as fairly presenting the financial condition, results
of operations and cash flows of the MLP or the Borrower, as applicable, and
their respective Subsidiaries in accordance with GAAP, subject only to normal
year-end audit adjustments and the absence of footnotes.

     6.02  CERTIFICATES; OTHER INFORMATION. Deliver to the Administrative Agent
and each Lender, in form and detail satisfactory to the Administrative Agent and
the Required Lenders:

     (a) concurrently with the delivery of the financial statements referred to
in SECTIONS 6.01(b), (c) and (d), a duly completed Compliance Certificate in
form of EXHIBIT C signed by a Responsible Officer of the Borrower and a
Responsible Officer of the MLP;

     (b) promptly after the same are available, copies of each annual report,
proxy or financial statement or other report or written communication sent to
the equity owners of the MLP, and copies of all annual, regular, periodic and
special reports and registration statements which the MLP may file or be

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required to file with the Securities and Exchange Commission under SECTION 13 or
15(d) of the Securities Exchange Act of 1934, and not otherwise required to be
delivered to the Administrative Agent pursuant hereto;

     (c)   promptly after execution thereof, copies of Material Agreements and
any material amendment thereto; and

     (d) promptly, such additional information regarding the business, financial
or corporate affairs of any Loan Party as the Administrative Agent, at the
request of any Lender, may from time to time reasonably request, which
information may include copies of any detailed audit reports, if any, management
letters or recommendations submitted to the board of directors (or the audit
committee of the board of directors) of the Borrower by independent accountants
in connection with the accounts or books of the Borrower or any Subsidiary, or
any audit of any of them.

     6.03  NOTICES. Promptly notify the Administrative Agent and each Lender:

     (a)   of the occurrence of any Default or Event of Default, as soon as
possible but in any event within ten (10) days after the occurrence thereof;

     (b) of any matter that has resulted or could reasonably be expected to
result in a Material Adverse Effect, including any of the following events if
such has resulted or could reasonably be expected to result in a Material
Adverse Effect: (i) breach or non-performance of, or any default under, a
Contractual Obligation of any Loan Party; (ii) any litigation, investigation by
or required by a Governmental Authority, proceeding or suspension of licenses or
permits between any Loan Party and any Governmental Authority; (iii) any
dispute, litigation, investigation or proceeding involving any Loan Party
related to any Environmental Law;

     (c) of any litigation, investigation or proceeding known to and affecting
the Borrower or any Borrower Affiliate in which (i) the amount involved exceeds
(individually or collectively) $3,500,000, or (ii) injunctive relief or other
relief is sought, which could be reasonably expected to have a Material Adverse
Effect; and

     (d)   of any material change in accounting policies or financial reporting
practices by the Borrower or the MLP.

     Each notice pursuant to this Section shall be accompanied by a statement of
a Responsible Officer of the Borrower setting forth details of the occurrence
referred to therein and stating what action the Borrower has taken and proposes
to take with respect thereto. Each notice pursuant to SECTION 6.03(a) shall
describe with particularity any and all provisions of this Agreement or other
Loan Document that have been breached.

     6.04 PAYMENT OF OBLIGATIONS. Pay and discharge as the same shall become due
and payable, all its obligations and liabilities, including (a) all tax
liabilities, assessments and governmental charges or levies upon it or its
properties or assets and (b) all lawful claims which, if unpaid, would by law
become a Lien upon its property, except, in the case of Clause (a) or (b), where
(x) the validity thereof are being contested in good faith by appropriate
proceedings and (y) adequate reserves in accordance with GAAP are being
maintained by the appropriate Loan Party.

     6.05  PRESERVATION OF EXISTENCE, ETC. (a) Preserve, renew and maintain in
full force and effect its legal existence and good standing under the Laws of
the jurisdiction of its organization, except in a

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transaction permitted by SECTIONS 7.06 and 7.07, (b) take all reasonable action
to maintain all rights, privileges, permits, licenses and franchises material to
the conduct of its business, except in a transaction permitted by SECTIONS 7.06
and 7.07.

     6.06 MAINTENANCE OF ASSETS AND BUSINESS. (a) Maintain all material
properties, equipment, licenses, permits, and franchises necessary for its
normal business; (b) keep all of its assets which are useful in and necessary to
its business in good working order and condition (ordinary wear and tear
excepted) and make all necessary repairs thereto and replacements thereof; (c)
do all things necessary to obtain, renew, extend, and continue in effect all
Authorizations which may at any time and from time to time be necessary for the
operation of its business in compliance with applicable Law, except where the
failure to so maintain, renew, extend, or continue in effect could not
reasonably be expected to have a Material Adverse Effect; (d) preserve or renew
all of its registered patents, trademarks, trade names and service marks, the
non-preservation of which could reasonably be expected to have a Material
Adverse Effect; and (e) use the standard of care typical in the industry in the
operation and maintenance of its facilities.

     6.07 MAINTENANCE OF INSURANCE. (a) Maintain with responsible insurance
companies insurance with respect to its properties and business (including
business interruption insurance) against such casualties and contingencies and
of such types and in such amounts as is customary in the case of similar
businesses and which is satisfactory to the Administrative Agent and the
Required Lenders and will (i) furnish to the Administrative Agent on each
anniversary of the Effective Date a certificate or certificates of insurance
from the applicable insurance company evidencing the existence of insurance
required to be maintained by this Agreement and the other Loan Documents and
evidencing that Administrative Agent is listed as sole loss payee on property
insurance (except as to properties owned by MarkWest Parent or the MarkWest Inc.
Operating Subsidiaries (as defined in the Parent Credit Agreement)) and the
Administrative Agent and Lenders are additional insureds on liability insurance,
and (ii) upon request of the Administrative Agent, furnish to each Lender at
reasonable intervals a certificate of an Authorized Officer of the Borrower
setting forth the nature and extent of all insurance maintained in accordance
with this Section.

     (b) (i) Except as the Administrative Agent may otherwise consent to in
writing, Borrower will, and will cause each of its Subsidiaries to, forthwith
upon receipt, transmit and deliver to the Administrative Agent, in the form
received, all cash, checks, drafts, chattel paper and other instruments or
writings for the payment of money (properly endorsed, where required, so that
such items may be collected by the Administrative Agent) which may be received
by the Borrower at any time in full or partial payment of amounts due under any
insurance policy. Except as the Administrative Agent may otherwise consent in
writing, any such items which may be received by the Borrower will not be
commingled with any other of its funds or property, but will be held separate
and apart from its own funds or property and upon express trust for the
Administrative Agent until delivery is made to the Administrative Agent.
Borrower will comply with the terms and conditions of any consent given by the
Administrative Agent pursuant to the provisions of this paragraph.

     All items or amounts in excess of $250,000 which are delivered by the
Borrower or by any insurance company to the Administrative Agent on account of
partial or full payment of amounts due under any insurance policy shall be
deposited to the credit of a deposit account (herein called the "INSURANCE
DEPOSIT ACCOUNT") of the Borrower with the Administrative Agent, as security for
payment of the Obligations. Borrower shall have no right to withdraw any funds
deposited in the Insurance Deposit Account. Administrative Agent will apply all
or any of the then balance in the Insurance Deposit Account toward payment of
the Obligations, in such order of application as the Administrative Agent may
determine. Administrative Agent may, from time to time, in its reasonable
discretion and with the

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consent of the Required Lenders, release all or any of such balance representing
collected funds to the Borrower. Administrative Agent is authorized to endorse,
in the name of the Borrower, any item, howsoever received by the Administrative
Agent, representing any payment under any insurance policy.

           (ii) The Borrower hereby grants to the Administrative Agent, for the
benefit of the Lenders, a lien on and security interest in and to such account
and all monies, cash, checks, drafts, certificates of deposit, instruments,
investment property, and other items ever received by Administrative Agent for
deposit therein and held therein, as security for the Obligations. The rights
granted by this SECTION 6.07 shall be in addition to the rights of the
Administrative Agent under any statutory banker's Lien or the common law right
of setoff.

     6.08 COMPLIANCE WITH LAWS AND CONTRACTUAL OBLIGATIONS. (a) Comply in all
material respects with the requirements of all Laws (including Environmental
Laws) applicable to it or to its business or property, except in such instances
in which (i) such requirement of Law is being contested in good faith or a bona
fide dispute exists with respect thereto; or (ii) the failure to comply
therewith could not be reasonably expected to have a Material Adverse Effect;
and (b) comply with all Contractual Obligations, except the failure to comply
therewith could not be reasonably expected to have a Material Adverse Effect.

     6.09 BOOKS AND RECORDS. Maintain proper books of record and account, in
which full, true and correct entries in conformity with GAAP consistently
applied shall be made of all financial transactions and matters involving its
assets and business; and (b) maintain such books of record and account in
material conformity with all applicable requirements of any Governmental
Authority having regulatory jurisdiction over it.

     6.10 INSPECTION RIGHTS. Permit representatives and independent contractors
of the Administrative Agent and each Lender to visit and inspect any of its
properties, to examine its corporate, financial and operating records, and make
copies thereof or abstracts therefrom, and to discuss its affairs, finances and
accounts with its directors, officers, and independent public accountants, at
such reasonable times during normal business hours and as often as may be
reasonably desired, upon reasonable advance notice to the Borrower; PROVIDED,
HOWEVER, that when an Event of Default exists the Administrative Agent or any
Lender (or any of their respective representatives or independent contractors)
may do any of the foregoing at the expense of the Borrower at any time during
normal business hours and without advance notice.

     6.11 COMPLIANCE WITH ERISA. With respect to each Plan maintained by a
Company, do each of the following: (a) maintain each Plan in compliance in all
material respects with the applicable provisions of ERISA, the Code and other
federal or state Laws, (b) cause each Plan which is qualified under SECTION
401(a) of the Code to maintain such qualification, and (c) make all required
contributions to any Plan subject to SECTION 412 of the Code, except to the
extent that noncompliance, with respect to each event listed above, could not be
reasonably expected to have a Material Adverse Effect.

     6.12  USE OF PROCEEDS. (a) Use the proceeds of the Term Loan Facility to
finance the purchase of the Purchased Assets;

     (b) Use the proceeds of the Acquisition Subfacility as follows (i) to
finance Acquisitions and Capital Expenditures by the Borrower and its
Subsidiaries of Persons or assets subject to compliance with this Agreement,
including SECTIONS 7.02 and 7.10, and (ii) on the Initial Funding Date, the
Borrower may request a Borrowing in an amount not to exceed $5,600,000 to
finance a portion of the Purchased Assets; and

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     (c) Use the proceeds (including Letters of Credit) of the Working
Capital/Distribution Subfacility to (i) fund working capital requirements of the
Borrower and its Subsidiaries, (ii) fund Quarterly Distributions to the extent
permitted by SECTIONS 2.01(c) and 7.08(b) and (c) and (iii) pay fees, costs and
expenses owed pursuant to this Agreement and incurred pursuant to the MLP
Offering.

     6.13 MATERIAL AGREEMENTS. Enforce the obligations of MarkWest contained in
the indemnification provisions of the Omnibus Agreement, and enforce all other
obligations of the MarkWest Parties contained in the Material Agreements to the
same extent as they would enforce similar obligations of unrelated third
parties.

     6.14 CLEAN DOWN PERIOD. During each calendar year, there shall be a period
of fifteen (15) consecutive days (the "CLEAN DOWN PERIOD") during which (a)
there are no Loans outstanding under the Working Capital/Distribution
Subfacility, and (b) no Loans will be made under the Working
Capital/Distribution Subfacility.

     6.15 GUARANTIES. As an inducement to the Administrative Agent and Lenders
to enter into this Agreement, cause each Subsidiary and the MLP to execute and
deliver to Administrative Agent a Guaranty executed by the Borrower's
Subsidiaries and the MLP's Subsidiaries (other than the Borrower), and a
Guaranty executed by the MLP, each substantially in the form and upon the terms
of EXHIBIT E-1 and EXHIBIT E-2, respectively, providing for the guaranty of
payment and performance of the Obligations; and a Guaranty executed by MarkWest
Parent providing for the guaranty of payment and performance of the Obligations
accruing from the Closing Date until the Conditions Effective Date. In addition,
at the time of the formation or acquisition of any Subsidiary, cause such
Subsidiary to execute and deliver to the Administrative Agent (a) a Guaranty
substantially in the form and upon the terms of EXHIBIT E-1, providing for the
guaranty of payment and performance of the Obligations, (b) Collateral Documents
in form and substance satisfactory to the Administrative Agent creating liens
and security interests in all assets and properties of such Subsidiary and in
the equity interests in such Subsidiary, and (c) certified copies of such
Subsidiary's Organization Documents and opinions of counsel with respect to such
Subsidiary and such Guaranty, in substantially the forms of EXHIBIT F-1, F-2,
and F-3 hereto, and (d) such other documents and instruments as may be required
with respect to such Subsidiary pursuant to SECTION 6.16.

     6.16 FURTHER ASSURANCES; ADDITIONAL COLLATERAL. (a) The Borrower and the
MLP shall cause the MLP and each Subsidiary of the Borrower and the MLP to take
such actions and to execute and deliver such documents and instruments as the
Administrative Agent shall require to ensure that the Administrative Agent on
behalf of the Lenders shall, at all times, have received currently effective
duly executed Loan Documents granting Lien and security interest in
substantially all of the assets of the MLP and each Subsidiary of the Borrower
and the MLP, including all capital stock, partnership, joint venture, membership
interests, or other equity interest; provided, however that MarkWest Energy
Appalachia, L.L.C. shall not be required to grant a Lien on its interests in the
Equitable Leases.

     (b) In connection with the actions required pursuant to the foregoing
subsection (a), the Borrower and the MLP shall cause the MLP and each Subsidiary
of the Borrower and the MLP to execute and deliver such stock certificates,
blank stock powers, evidence of corporate authorization, opinions of counsel,
current valuations, evidence of title, title opinions, title insurance and other
documents, and shall use commercially reasonable efforts to obtain landlord and
mortgagee waivers and third party consents, as shall be requested by the
Administrative Agent, in each case in form and substance satisfactory to the
Administrative Agent.

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     (c) The Liens required by this SECTION 6.16 shall be first priority
perfected Liens in favor of the Administrative Agent for the benefit of the
Lenders, subject to no other Liens except Permitted Liens of the type described
in SECTION 7.01 (other than SECTION 7.01(h)). If the Administrative Agent shall
determine that, as of any date, the Borrower or the MLP shall have failed to
comply with this SECTION 6.16, the Administrative Agent may (and at the
direction of the Required Lenders, shall) notify the Borrower in writing of such
failure and, within 30 days from and after receipt of such written notice by the
Borrower, the Borrower shall execute and deliver to the Administrative Agent
supplemental or additional Loan Documents, in form and substance satisfactory to
the Administrative Agent and its counsel, securing payment of the Notes and the
other Obligations and covering additional assets and properties not then
encumbered by any Loan Documents (together with such other information, as may
be requested by the Administrative Agent, each of which shall be in form and
substance reasonably satisfactory to the Administrative Agent) such that the
Administrative Agent shall have received currently effective duly executed and
perfected Collateral Documents encumbering substantially all of the assets of
the MLP, Borrower and their respective Subsidiaries as required by SECTION
6.16(a).

                                  ARTICLE VII.
                               NEGATIVE COVENANTS

     So long as any Lender shall have any Commitment hereunder, or any Loan or
other Obligations shall remain unpaid or unsatisfied, or any Letter of Credit
shall remain outstanding, each of the MLP and the Borrower agree that they shall
not, nor shall they permit any of their respective Subsidiaries to, directly or
indirectly:

     7.01 LIENS. Create, incur, assume or suffer to exist, any Lien upon any of
its property, assets or revenues, whether now owned or hereafter acquired, other
than the following:

     (a)   Liens pursuant to any Loan Document;

     (b) Liens existing on the Conditions Effective Date and listed on SCHEDULE
7.01 and any renewals or extensions thereof, PROVIDED that the property covered
thereby is not increased, the amount of the Indebtedness secured thereby is not
increased, and any renewal or extension of the obligations secured or benefited
thereby is permitted under this Agreement;

     (c) Liens for taxes not yet due or which are being contested in good faith
and by appropriate proceedings, if adequate reserves with respect thereto are
maintained on the books of the applicable Person in accordance with GAAP;

     (d) carriers', warehousemen's, mechanics', materialmen's, repairmen's or
other like Liens arising in the ordinary course of business which are not
overdue for a period of more than 30 days or which are being contested in good
faith and by appropriate proceedings, if adequate reserves with respect thereto
are maintained on the books of the applicable Person;

     (e) pledges or deposits in the ordinary course of business in connection
with workers' compensation, unemployment insurance and other social security
legislation, other than any Lien imposed by ERISA;

     (f) deposits to secure the performance of bids, trade contracts (other than
for borrowed money), leases, statutory obligations, surety and appeal bonds,
performance bonds and other obligations of a like nature, in each case incurred
in the ordinary course of business;

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     (g) easements, rights-of-way, restrictions and other similar encumbrances
affecting real property which do not in any case materially detract from the
value of the property subject thereto or materially interfere with the ordinary
conduct of the business of the applicable Person;

     (h)   judgment Liens not giving rise to an Event of Default;

     (i) any Lien existing on any asset (other than stock of a Subsidiary) prior
to acquisition thereof by the Borrower or a Subsidiary, and not created in
contemplation of such acquisition, provided that (i) no such Lien shall be
extended to cover property other than the asset being acquired, (ii) such Lien
was not created in contemplation of or in connection with such acquisition,
(iii) the Indebtedness thereby secured is permitted by SECTION 7.04(d), and (iv)
the fair market value of such asset shall at no time exceed 150% of the
Indebtedness thereby secured;

     (j) Liens securing Capitalized Lease obligations PROVIDED THAT the
Indebtedness in respect of such Capitalized Lease is permitted under SECTION
7.04(d);

     (k) Purchase money Liens upon or in any property acquired by Borrower or
any of its Subsidiaries to secure the deferred portion of the purchase price of
such property or to secure Indebtedness incurred to finance the acquisition of
such property, PROVIDED THAT (i) no such Lien shall be extended to cover
property other than the property being acquired, and (ii) the Indebtedness
thereby secured is permitted by SECTION 7.04(d);

     (l) Liens reserved in or exercisable under any lease or sublease to which
the Borrower or a Subsidiary is a lessee which secure the payment of rent or
compliance with the terms of such lease or sublease; PROVIDED, that the rent
under such lease or sublease is not then overdue and the Borrower or Subsidiary
is in material compliance with the terms and conditions thereof;

     (m) any interest or title of a lessor under any lease entered into by the
Borrower or any Subsidiary in the ordinary course of its business and covering
only the assets so leased; and

     (n) Liens incurred in the ordinary course of business in connection with
margin requirements under Lender Hedging Agreements not to exceed in the
aggregate $3,000,000 at any time outstanding.

     7.02  INVESTMENTS. Make or own any Investments, except:

     (a)   Investments existing on the Conditions Effective Date and listed in
Section (b) of SCHEDULE 5.13;

     (b)   Cash Equivalents;

     (c)   Investments constituting Indebtedness permitted under
           SECTION 7.04(b);

     (d)   Investments by the MLP in the Borrower;

     (e)   Acquisitions of not more than 5% of the outstanding equity securities
of any Person;

     (f)   Investments by the Borrower and its Subsidiaries in any Subsidiary of
the Borrower that, prior to such Investment, is a Guarantor;

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     (g)   Acquisition of assets by the Borrower on the Conditions Effective
Date pursuant to the Contribution Agreement;

     (h)   trade accounts receivable which are for goods furnished or services
rendered in the ordinary course of business; and

     (i)   Permitted Acquisitions by the Borrower or its Subsidiaries.

     7.03 HEDGING AGREEMENTS. Enter into any Swap Contracts other than in the
ordinary course of business for the purpose of protecting against fluctuations
in interest rates, commodity prices, or foreign exchange rates and not for
purposes of speculation, provided that the Swap Contract shall not contain any
provision exonerating the non-defaulting party from its obligation to make
payments on outstanding transactions to the defaulting party.

     7.04  INDEBTEDNESS.

     Create, incur, or assume any Indebtedness except:

     (a)   Indebtedness incurred pursuant to the Loan Documents;

     (b) Indebtedness owed by a Subsidiary to the Borrower or to a Wholly-Owned
Subsidiary or by the Borrower to a Wholly-Owned Subsidiary of the Borrower,
PROVIDED, THAT, in each such case such Indebtedness is evidenced by a promissory
note which has been pledged to secure the Obligations and is in the possession
of the Administrative Agent;

     (c) Other Indebtedness of the Borrower and the MLP ("REFINANCING
INDEBTEDNESS") not to exceed $30,000,000 in aggregate principal amount
outstanding at any time, which Refinancing Indebtedness shall be subordinated to
the Obligations pursuant to a subordination agreement in form and substance
satisfactory to the Administrative Agent and the Lenders in their sole
discretion (a "SUBORDINATION AGREEMENT"), PROVIDED that such Refinancing
Indebtedness shall bear a market rate of interest and shall not require any
payment of principal earlier than six (6) months after the Stated Maturity Date
and the Net Cash Proceeds thereof shall be used to prepay the Loans and reduce
the Commitments pursuant to SECTION 2.04(b);

     (d) obligations (contingent or otherwise) of the Borrower, the MLP or any
Subsidiary existing or arising under any Swap Contract to the extent permitted
by SECTION 7.03; and

     (e) Indebtedness in respect of purchase money obligations for fixed or
capital assets within the limitations set forth in SECTION 7.01(i); PROVIDED,
HOWEVER, that the aggregate amount of such Indebtedness at any one time
outstanding shall not exceed $5,000,000;

     (f) Other Indebtedness of the MLP, the Borrower and their respective
Subsidiaries not to exceed $5,000,000 in aggregate principal amount outstanding
at any time.

PROVIDED, that if any Indebtedness is incurred pursuant to this SECTION 7.04,
both before and after such Indebtedness is created, incurred or assumed, no
Default or Event of Default shall exist.

     7.05 LEASE OBLIGATIONS. Create or suffer to exist any obligations for the
payment of rent for any property under lease or agreement to lease, except for
operating leases (other than those constituting Synthetic Lease Obligations)
entered into or assumed by the Borrower or any Subsidiary after the date

                                       56
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hereof in the ordinary course of business, PROVIDED THAT, such operating leases
will not require the payment of an aggregate amount of payments in excess of
(excluding escalations resulting from a rise in the consumer price or similar
index) $7,500,000 during the full remaining term of such Leases, exclusive of
expenses for maintenance, repairs, insurance taxes, assessments and similar
changes.

     7.06 FUNDAMENTAL CHANGES. Merge or consolidate with or into, or convey,
transfer, lease or otherwise dispose of (whether in one transaction or in a
series of transactions) all or substantially all of its assets (whether now
owned or hereafter acquired) to or in favor of any Person, except that, so long
as no Default or Event of Default exists or would result therefrom:

     (a)   any Person may merge into the Borrower PROVIDED THAT the Borrower is
the surviving entity;

     (b) any Subsidiary may merge with (i) the Borrower, PROVIDED THAT the
Borrower shall be the continuing or surviving Person, or (ii) any one or more
Subsidiaries, PROVIDED THAT when any Wholly-Owned Subsidiary is merging with
another Subsidiary, a Wholly-Owned Subsidiary shall be the continuing or
surviving Person;

     (c) any Subsidiary may sell all or substantially all of its assets (upon
voluntary liquidation or otherwise), to the Borrower or to another Subsidiary;
PROVIDED THAT if the seller in such a transaction is a Wholly-Owned Subsidiary,
then the purchaser must also be a Wholly-Owned Subsidiary; and

     (d) any Person (other than the Borrower or a Subsidiary of the Borrower)
may merge into any Subsidiary provided that such Subsidiary is the surviving
entity.

     7.07  DISPOSITIONS.

     Make any Disposition or enter into any agreement to make any Disposition,
except:

     (a)   Dispositions by the Borrower or its Subsidiaries of inventory in the
ordinary course of business;

     (b)   Dispositions of property by any Subsidiary to the Borrower, or by any
Subsidiary or by the Borrower, to a Wholly-Owned Subsidiary that is a Guarantor;
or

     (c) other Dispositions for fair market value, PROVIDED no Default or Event
of Default then exists or arises as a result thereof, PROVIDED THAT if the
Disposition is for cash and a prepayment is required by SECTION 2.04(b)(i), the
Borrower shall make such prepayment in accordance with such Section.

     7.08  RESTRICTED PAYMENTS; DISTRIBUTIONS AND REDEMPTIONS. Declare or make,
directly or indirectly, any Restricted Payment, or incur any obligation
(contingent or otherwise) to do so, except that:

     (a)   each Subsidiary may make Restricted Payments to the Borrower and to
Wholly-Owned Subsidiaries of the Borrower;

     (b) the Borrower may declare and make Quarterly Distributions of Available
Cash as defined in the Limited Liability Company Agreement (Borrower); PROVIDED,
that at the time each Quarterly Distribution is made no Default or Event of
Default exists or would result therefrom; and

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     (c) the MLP may declare and make Quarterly Distributions of Available Cash
as defined in the Partnership Agreement (MLP) to the extent such Quarterly
Distributions in any fiscal quarter do not exceed, in the aggregate, Available
Cash as defined in the Partnership Agreement (MLP) for the immediately preceding
fiscal quarter and are made in accordance with the Partnership Agreement (MLP);
PROVIDED, that at the time each such Quarterly Distribution is made no Default
or Event of Default exists or would result therefrom.

     7.09 ERISA. At any time engage in a transaction which could be subject to
SECTION 4069 or 4212(c) of ERISA, or permit any Plan maintained by a Company to
(a) engage in any non-exempt "PROHIBITED TRANSACTION" (as defined in SECTION
4975 of the Code); (b) fail to comply with ERISA or any other applicable Laws;
or (c) incur any material "ACCUMULATED FUNDING DEFICIENCY" (as defined in
SECTION 302 of ERISA), which, with respect to each event listed above, could be
reasonably expected to have a Material Adverse Effect.

     7.10 NATURE OF BUSINESS; CAPITAL EXPENDITURES. Engage in any line of
business other than the Midstream Business, or make any Capital Expenditures or
Acquisitions permitted by SECTION 7.02 except in connection with the Midstream
Business. The MLP may not engage in any business other than ownership of the
Borrower and the operation of the MLP.

     7.11 TRANSACTIONS WITH AFFILIATES. Sell, lease or otherwise transfer any
property or assets to, or purchase, lease or otherwise acquire any property or
assets from, or otherwise engage in any other transactions with, any of its
Affiliates, except (i) transactions between or among the Borrower and its
Wholly-Owned Subsidiaries not involving any other Affiliate, and (ii) any
Restricted Payment permitted by SECTION 7.08, and (iii) in the ordinary course
of business at prices and on terms and conditions not less favorable to the MLP,
the Borrower or such Subsidiary, as applicable, than could be obtained on an
arm's length basis from unrelated third parties.

     7.12 BURDENSOME AGREEMENTS. Enter into any Contractual Obligation that
limits the ability of any Subsidiary to make Restricted Payments to the Borrower
or to otherwise transfer property to the Borrower. Notwithstanding the
foregoing, (i) documents governing a Capitalized Lease or a purchase money Lien
permitted by SECTIONS 7.02(j) and (k) may prohibit other Liens on the asset
encumbered by such Lien, and (ii) the Lenders acknowledge that the real estate
leases described on SCHEDULE 7.12 restrict or prohibit Liens on the Borrower's
or its Subsidiary's leasehold interest.

     7.13 USE OF PROCEEDS. Use the proceeds of any Loan for purposes other than
those permitted by SECTION 6.12, or use the proceeds of any Loan, whether
directly or indirectly, and whether immediately, incidentally or ultimately, to
purchase or carry margin stock (within the meaning of Regulation U of the Board)
or to extend credit to others for the purpose of purchasing or carrying margin
stock or to refund indebtedness originally incurred for such purpose.

     7.14 MATERIAL AGREEMENTS. (a) Permit any amendment to any Borrower
Operating Agreement or any Material Agreement, if such amendment could
reasonably be expected to materially adversely affect the Lenders; or (b) permit
any assignment of any Material Agreement if such assignment could reasonably be
expected to materially adversely affect the Lenders or have a Material Adverse
Effect on the ability of the Borrower or any other Loan Party to perform its
obligations under the Loan Documents to which it is a party.

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     7.15  FINANCIAL COVENANTS.

     (a)   INTEREST COVERAGE RATIO. Permit the Interest Coverage Ratio as of the
end of any fiscal quarter to be less than the ratio of 3.5 to 1.0.

     (b)   LEVERAGE RATIO. Permit the Leverage Ratio at any time to be greater
than the ratio of 3.5 to 1.0.

     (c)   MINIMUM NET WORTH. Permit the net worth of the Borrower to be less
than the sum of (i) $40,000,000 and (ii) 75% of the proceeds of all equity
issued subsequent to the MLP Offering Closing.

     (d)   ADJUSTMENTS FOR ACQUISITIONS. For purposes of determining compliance
with SECTIONS 7.15(a) and (b):

           (i) Consolidated EBITDA shall be calculated after giving effect, on a
     pro forma basis for the four consecutive fiscal quarters most recently
     completed, to any Permitted Acquisition occurring during such period, as if
     such Permitted Acquisition occurred on the first day of such period;
     provided, however that if during any consecutive twelve (12) month period,
     the Purchase Price for Permitted Acquisitions by the Borrower and its
     Subsidiaries equals or exceeds $10,000,000 in the aggregate, then the
     EBITDA attributable to Over Threshold Acquisitions (herein defined) may be
     taken into account pursuant to this clause (d)(i) only if and to the extent
     permitted by the Required Lenders. "OVER THRESHOLD ACQUISITIONS" means all
     Permitted Acquisitions by the Borrower and its Subsidiaries for which the
     Purchase Price, when aggregated with the Purchase Price for all other
     Permitted Acquisitions during the twelve (12) month period in which such
     Permitted Acquisition occurs, equals or exceeds $10,000,000 in the
     aggregate.

           (ii) If, in connection with an Acquisition, any Indebtedness is
     incurred or assumed by a Company, then Consolidated Interest Charges shall
     be calculated, on a pro forma basis (in a manner acceptable to the Required
     Lenders) for the four quarters most recently completed, as if such
     Indebtedness had been incurred on the first day of such period.

     7.16 SUBORDINATED INDEBTEDNESS (REFINANCING INDEBTEDNESS). Neither the
Borrower nor the MLP will amend documents governing Refinancing Indebtedness
unless approved in writing by the Required Lenders (other than ministerial
amendments and amendments to extend the time or times for payment). The Borrower
shall not make any payments of interest or any other amounts in respect of the
Refinancing Indebtedness if a Default shall have occurred and be continuing or
would result from such payment. The Borrower will not repay any principal,
interest or other indebtedness in respect of the Refinancing Indebtedness, or
make any redemption or acquisition for value or defeasance, refinancing or
exchange thereof or therefore, or make any payments in contravention of the
applicable Subordination Agreement.

                                 ARTICLE VIII.
                         EVENTS OF DEFAULT AND REMEDIES

     8.01  EVENTS OF DEFAULT. Any of the following shall constitute an Event of
Default:

     (a)   NON-PAYMENT. The Borrower fails to pay (i) when and as required to be
paid herein, any amount of principal of any Loan or any L/C Obligation or (ii)
within three Business Days after the same

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becomes due, any interest on any Loan, any L/C Obligation, any commitment or
other fee due hereunder, or any other amount payable hereunder or under any
other Loan Document; or

     (b)   SPECIFIC COVENANTS. The Borrower fails to perform or observe any
term, covenant or agreement contained in any of SECTION 6.03(a), 6.05 (with
respect to the Borrower's existence), 6.12, 6.15, 6.16, or ARTICLE VII; or

     (c) OTHER DEFAULTS. Any Loan Party fails to perform or observe any other
covenant or agreement (not specified in subsection (a) or (b) above) contained
in any Loan Document on its part to be performed or observed and such failure
continues for 15 days after the earlier of (i) the date notice has been given to
the Borrower by the Administrative Agent or a Lender or (ii) the date a
Responsible Officer knew or reasonably should have known of such Default; or

     (d) REPRESENTATIONS AND WARRANTIES. Any representation or warranty made or
deemed made by the Borrower or any other Loan Party herein, in any other Loan
Document, or in any document delivered in connection herewith or therewith
proves to have been incorrect in any material respect when made or deemed made;
or

     (e) CROSS-DEFAULT. (i) The Borrower or any Borrower Affiliate (A) fails to
make any payment when due (whether by scheduled maturity, required prepayment,
acceleration, demand, or otherwise) in respect of any Indebtedness or Guaranty
Obligation (other than Indebtedness under Swap Contracts) having an aggregate
principal amount (or, in the case of a Capitalized Lease or a Synthetic Lease
Obligation, Attributable Indebtedness) (including undrawn or available amounts
and including amounts owing to all creditors under any combined or syndicated
credit arrangement) of more than (individually or collectively) $3,500,000, or
(B) fails to observe or perform any other agreement or condition relating to any
such Indebtedness or Guaranty Obligation or contained in any instrument or
agreement evidencing, securing or relating thereto, or any other event occurs,
the effect of which default or other event is to cause, or to permit the holder
or holders of such Indebtedness, the lessor under such Synthetic Lease
Obligation or the beneficiary or beneficiaries of such Guaranty Obligation (or a
trustee or agent on behalf of such holder or holders or beneficiary or
beneficiaries) to cause, with the giving of notice if required, such
Indebtedness to be demanded or to become due or to be repurchased or redeemed
(automatically or otherwise) prior to its stated maturity, or such Guaranty
Obligation to become payable or cash collateral in respect thereof to be
demanded; or (ii) (A) there occurs under any Swap Contract an Early Termination
Date (as defined in such Swap Contract) resulting from any event of default
under such Swap Contract as to which the Borrower or any Borrower Affiliate is
the Defaulting Party (as defined in such Swap Contract) and the Swap Termination
Value owed by the Borrower or any Borrower Affiliate as a result thereof is
greater than (individually or collectively) $3,500,000, or (B) there occurs
under any Swap Contract an Early Termination Date (as defined in such Swap
Contract) resulting from any Termination Event (as so defined) under such Swap
Contract as to which the Borrower or any Borrower Affiliate is an Affected Party
(as so defined) and the Swap Termination Value owed by the Borrower and Borrower
Affiliate as a result thereof is greater than (individually or collectively)
$3,500,000 and such amount is not paid when due under such Swap Contract; or

     (f) INSOLVENCY PROCEEDINGS, ETC. (i) The Borrower or any Borrower Affiliate
institutes or consents to the institution of any proceeding under any Debtor
Relief Law, or makes an assignment for the benefit of creditors; or applies for
or consents to the appointment of any receiver, trustee, custodian, conservator,
liquidator, rehabilitator or similar officer for it or for all or any material
part of its property or takes any action to effect any of the foregoing; or (ii)
any receiver, trustee, custodian, conservator, liquidator, rehabilitator or
similar officer is appointed without the application or consent of such Person
and the appointment continues undischarged or unstayed for 60 calendar days; or
(iii) any proceeding

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under any Debtor Relief Law relating to any such Person or to all or any part of
its property is instituted without the consent of such Person and continues
undismissed or unstayed for 60 calendar days, or an order for relief is entered
in any such proceeding; or

     (g) INABILITY TO PAY DEBTS; ATTACHMENT. (i) The Borrower or any Borrower
Affiliate becomes unable or admits in writing its inability or fails generally
to pay its debts as they become due, or (ii) any writ or warrant of attachment
or execution or similar process is issued or levied against property which is a
material part of the property of the Borrower and its Subsidiaries taken as a
whole, and is not released, vacated or fully bonded within 45 days after its
issue or levy; or

     (h) JUDGMENTS. There is entered against the Borrower or any Borrower
Affiliate (i) a final judgment or order for the payment of money in an aggregate
amount exceeding (individually or collectively) $3,500,000 (to the extent not
covered by third-party insurance as to which the insurer does not dispute
coverage), or (ii) any non-monetary final judgment that has or could reasonably
be expected to have a Material Adverse Effect and, in either case, (A)
enforcement proceedings are commenced by any creditor upon such judgment or
order, or (B) there is a period of 30 consecutive days during which a stay of
enforcement of such judgment, by reason of a pending appeal or otherwise, is not
in effect; or

     (i) ERISA. (i) If the Borrower, any Borrower Affiliate or any of their
ERISA Affiliates maintains any Pension Plan or any Multiemployer Plan, an ERISA
Event occurs with respect to a Pension Plan or Multiemployer Plan which has
resulted or could reasonably be expected to result in liability of the Borrower
or any Borrower Affiliate under TITLE IV of ERISA to the Pension Plan,
Multiemployer Plan or the PBGC in an aggregate amount in excess of $3,500,000,
or (ii) if there is any Multiemployer Plan, the Borrower, any Borrower Affiliate
or any ERISA Affiliate thereof fails to pay when due, after the expiration of
any applicable grace period, any installment payment with respect to its
withdrawal liability under SECTION 4201 of ERISA under a Multiemployer Plan in
an aggregate amount in excess of $3,500,000; or

     (j) INVALIDITY OF LOAN DOCUMENTS. Any Loan Document, at any time after its
execution and delivery and for any reason other than the agreement of all the
Lenders or termination of all Commitments and satisfaction in full of all the
Obligations, ceases to be in full force and effect, or is declared by a court of
competent jurisdiction to be null and void, invalid or unenforceable in any
material respect; or any Loan Party denies that it has any or further liability
or obligation under any Loan Document, or purports to revoke, terminate or
rescind any Loan Document; or

     (k)   CHANGE OF CONTROL. There occurs any Change of Control; or

     (l)   DISSOLUTION. The Borrower or any Borrower Affiliate shall dissolve,
liquidate, or otherwise terminate its existence, except as permitted in SECTION
7.06; or

     (m) MATERIAL AGREEMENTS. (i) Termination of any Material Agreement, any
Parent Material Agreement, or any material provision of any of the foregoing if
such termination could reasonably be expected to have a Material Adverse Effect
and such agreement or provision is not replaced (prior to such cessation) in a
manner satisfactory to the Required Lenders; (ii) default by any Person in the
performance or observance of any material term of any Material Agreement or any
Parent Material Agreement which is not cured within the applicable cure period
specified in such Material Agreement or such Parent Material Agreement, if such
default could reasonably be expected to have a Material Adverse Effect; (iii)
any Unauthorized Assignment shall occur; or (iv) any event or condition occurs
or exists which in the opinion of the Required Lenders is reasonably likely to
(x) have a material adverse effect on the ability of

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a MarkWest Party to perform its obligations under a Material Agreement or under
a Parent Material Agreement and (y) result in a Material Adverse Effect
hereunder; or

     (n) COLLATERAL; IMPAIRMENT OF SECURITY, ETC. (i) Any provision of any Loan
Document shall for any reason cease to be valid and binding on or enforceable
against a Loan Party or any Loan Party shall so state in writing or bring an
action to limit its obligations or liabilities thereunder; or (ii) any
Collateral Document shall for any reason (other than pursuant to the terms
thereof) cease to create a valid security interest in the Collateral purported
to be covered thereby or such security interest shall for any reason cease to be
a perfected and first priority security interest subject to Permitted Liens; or
(iii) any provision of a Subordination Agreement shall cease to be effective or
shall not be enforceable, or any holder of Refinancing Indebtedness shall seek
to invalidate any provision of a Subordination Agreement.

     8.02  REMEDIES UPON EVENT OF DEFAULT. If any Event of Default occurs, the
Administrative Agent shall, at the request of, or may, with the consent of, the
Required Lenders:

     (a) declare the commitment of each Lender to make Loans and any obligation
of the L/C Issuer to make L/C Credit Extensions to be terminated, whereupon such
commitments and obligations shall be terminated;

     (b) declare the unpaid principal amount of all outstanding Loans, all
interest accrued and unpaid thereon, and all other amounts owing or payable
hereunder or under any other Loan Document to be immediately due and payable,
without presentment, demand, protest, notice of intent to accelerate, notice of
acceleration or other notice of any kind, all of which are hereby expressly
waived by the Borrower;

     (c) declare that an amount equal to the then Outstanding Amount of all L/C
Obligations be immediately due and payable by the Borrower, without presentment,
demand, protest, notice of intent to accelerate, notice of acceleration or other
notice of any kind, all of which are hereby expressly waived by the Borrower,
and require that the Borrower deliver such payments to the Administrative Agent
to Cash Collateralize the L/C Obligations (in an amount equal to the then
Outstanding Amount thereof); and

     (d)   exercise on behalf of itself and the Lenders all rights and remedies
available to it and the Lenders under the Loan Documents or applicable law;

PROVIDED, HOWEVER, that upon the occurrence of any event specified in subsection
(f) of SECTION 8.01, the obligation of each Lender to make Loans and any
obligation of the L/C Issuer to make L/C Credit Extensions shall automatically
terminate, the unpaid principal amount of all outstanding Loans and all interest
and other amounts as aforesaid shall automatically become due and payable, and
an amount equal to the then Outstanding Amount of all L/C Obligations shall be
deemed to be forthwith due and owing by the Borrower to the Issuing Bank and the
Lenders as of the date of such occurrence and the Borrower's obligation to pay
such amounts shall be absolute and unconditional, without regard to whether any
beneficiary of any such Letter of Credit has attempted to draw down all or a
portion of such amount under the terms of a Letter of Credit and, to the fullest
extent permitted by applicable law, shall not be subject to any defense or be
affected by a right of set-off, counterclaim or recoupment which the Borrower
may now or hereafter have against any such beneficiary, the Issuing Bank, the
Administrative Agent, the Lenders or any other Person for any reason whatsoever.
Such payments shall be delivered to and held by the Administrative Agent as cash
collateral securing the L/C Obligations.

                                  ARTICLE IX.
                              ADMINISTRATIVE AGENT

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     9.01 APPOINTMENT AND AUTHORIZATION OF ADMINISTRATIVE AGENT; LENDER HEDGING
AGREEMENTS. (a) Each Lender hereby irrevocably (subject to SECTION 9.10)
appoints, designates and authorizes the Administrative Agent to take such action
on its behalf under the provisions of this Agreement and each other Loan
Document and to exercise such powers and perform such duties as are expressly
delegated to it by the terms of this Agreement or any other Loan Document,
together with such powers as are reasonably incidental thereto. Notwithstanding
any provision to the contrary contained elsewhere herein or in any other Loan
Document, the Administrative Agent shall not have any duties or
responsibilities, except those expressly set forth herein, nor shall the
Administrative Agent have or be deemed to have any fiduciary relationship with
any Lender or participant, and no implied covenants, functions,
responsibilities, duties, obligations or liabilities shall be read into this
Agreement or any other Loan Document or otherwise exist against the
Administrative Agent. Without limiting the generality of the foregoing sentence,
the use of the term "AGENT" herein and in the other Loan Documents with
reference to the Administrative Agent is not intended to connote any fiduciary
or other implied (or express) obligations arising under agency doctrine of any
applicable law. Instead, such term is used merely as a matter of market custom,
and is intended to create or reflect only an administrative relationship between
independent contracting parties.

     (b) The L/C Issuer shall act on behalf of the Lenders with respect to any
Letters of Credit issued by it and the documents associated therewith until such
time (and except for so long) as the Administrative Agent may agree at the
request of the Required Lenders to act for the L/C Issuer with respect thereto;
PROVIDED, HOWEVER, that the L/C Issuer shall have all of the benefits and
immunities (i) provided to the Administrative Agent in this ARTICLE IX with
respect to any acts taken or omissions suffered by the L/C Issuer in connection
with Letters of Credit issued by it or proposed to be issued by it and the
application and agreements for letters of credit pertaining to the Letters of
Credit as fully as if the term "Administrative Agent" as used in this ARTICLE IX
included the L/C Issuer with respect to such acts or omissions, and (ii) as
additionally provided herein with respect to the L/C Issuer.

     (c) To the extent any Lender or any Affiliate of a Lender is a party to a
Lender Hedging Agreement and accepts the benefits of the Liens in the Collateral
arising pursuant to the Collateral Documents, such Lender (for itself and on
behalf of any such Affiliates) shall be deemed (i) to appoint Bank of America,
N.A., as its nominee and agent, to act for and on behalf of such Lender or
Affiliate thereof in connection with the Collateral Documents and (ii) to be
bound by the terms of this ARTICLE IX.

     9.02 DELEGATION OF DUTIES. The Administrative Agent may execute any of its
duties under this Agreement or any other Loan Document by or through agents,
employees or attorneys-in-fact and shall be entitled to advice of counsel and
other consultants or experts concerning all matters pertaining to such duties.
The Administrative Agent shall not be responsible for the negligence or
misconduct of any agent or attorney-in-fact that it selects in the absence of
gross negligence or willful misconduct.

     9.03 DEFAULT; COLLATERAL; AGREEMENT REGARDING COLLATERAL. (a) Upon the
occurrence and continuance of a Default or Event of Default, the Lenders agree
to promptly confer in order that Required Lenders or the Lenders, as the case
may be, may agree upon a course of action for the enforcement of the rights of
the Lenders; and the Administrative Agent shall be entitled to refrain from
taking any action (without incurring any liability to any Person for so
refraining) UNLESS and until the Administrative Agent shall have received
instructions from Required Lenders. All rights of action under the Loan
Documents and all right to the Collateral, if any, hereunder may be enforced by
the Administrative Agent and any suit or proceeding instituted by the
Administrative Agent in furtherance of such enforcement shall be brought in its
name as the Administrative Agent without the necessity of joining as plaintiffs
or defendants any other Lender, and the recovery of any judgment shall be for
the

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benefit of the Lenders (and, with respect to Lender Hedging Agreements,
Affiliates, if applicable) subject to the expenses of the Administrative Agent.
In actions with respect to any property of the Borrower or any other Obligor,
the Administrative Agent is acting for the ratable benefit of each Lender (and,
with respect to Lender Hedging Agreement, Affiliates, if applicable). Any and
all agreements to subordinate (whether made heretofore or hereafter) other
indebtedness or obligations of Borrower to the Obligation shall be construed as
being for the ratable benefit of each Lender (and, with respect to Lender
Hedging Agreement, Affiliates, if applicable).

     (b) Each Lender authorizes and directs the Administrative Agent to enter
into the Agreement Regarding Collateral and the Collateral Documents on behalf
of and for the benefit of the Lenders (and, with respect to Lender Hedging
Agreement, Affiliates, if applicable).

     (c) EXCEPT to the extent unanimity (or other percentage set forth in
SECTION 10.1) is required hereunder, each Lender agrees that any action taken by
the Required Lenders in accordance with the provisions of the Loan Documents,
and the exercise by the Required Lenders of the power set forth herein or
therein, TOGETHER WITH such other powers as are reasonably incidental thereto,
shall be authorized and binding upon all of the Lenders.

     (d) The Administrative Agent is hereby authorized on behalf of the Lenders,
without the necessity of any notice to or further consent from any Lender, from
time to time to take any action with respect to any Collateral or Collateral
Documents which may be necessary to perfect and maintain perfected the Liens
upon the Collateral granted pursuant to the Collateral Documents.

     (e) The Administrative Agent shall have no obligation whatsoever to any
Lender or to any other Person to assure that the Collateral exists or is owned
by any Obligor or is cared for, protected, or insured or has been encumbered or
that the Liens granted to the Administrative Agent herein or pursuant thereto
have been properly or sufficiently or lawfully created, perfected, protected, or
enforced, or are entitled to any particular priority, or to exercise at all or
in any particular manner or under any duty of care, disclosure, or fidelity, or
to continue exercising, any of the Rights granted or available to the
Administrative Agent in this SECTION 9.03 or in any of the Collateral Documents;
IT BEING UNDERSTOOD and agreed that in respect of the Collateral, or any act,
omission, or event related thereto, the Administrative Agent may act in any
manner it may deem appropriate, in its sole discretion, given the Administrative
Agent's own interest in the Collateral as one of the Lenders and that the
Administrative Agent shall have no duty or liability whatsoever to any Lender,
OTHER THAN to act without gross negligence or willful misconduct.

     (f) The Lenders hereby irrevocably authorize the Administrative Agent, at
its option and in its discretion, to release any Lien granted to or held by the
Administrative Agent upon any Collateral: (i) constituting property in which no
Obligor owned an interest at the time the Lien was granted or at any time
thereafter; (ii) constituting property leased to an Obligor under a lease which
has expired or been terminated in a transaction permitted under the Loan
Document or is about to expire and which has not been, and is not intended by
such Obligor to be, renewed; and (iii) consisting of an instrument evidencing
Indebtedness pledged to the Administrative Agent (for the benefit of the
Lenders), if the Indebtedness evidenced thereby has been paid in full. In
addition, the Lenders irrevocably authorize the Administrative Agent to release
Liens upon Collateral as contemplated in SECTION 10.01(c) or (d), or if
approved, authorized, or ratified in writing by the requisite Lenders. Upon
request by the Administrative Agent at any time, the Lenders will confirm in
writing the Administrative Agent's authority to release particular types or
items of Collateral pursuant to this SECTION 9.03.

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     (g) In furtherance of the authorizations set forth in this SECTION 9.03,
each Lender hereby irrevocably appoints the Administrative Agent its
attorney-in-fact, with full power of substitution, for and on behalf of and in
the name of each such Lender, (i) to enter into Collateral Documents (including,
without limitation, any appointments of substitute trustees under any Collateral
Documents), (ii) to take action with respect to the Collateral and Collateral
Documents to perfect, maintain, and preserve Lenders' Liens, and (iii) to
execute instruments of release or to take other action necessary to release
Liens upon any Collateral to the extent authorized in paragraph (e) hereof. This
power of attorney shall be liberally, not restrictively, construed so as to give
the greatest latitude to the Administrative Agent's power, as attorney, relative
to the Collateral matters described in this SECTION 9.03. The powers and
authorities herein conferred on the Administrative Agent may be exercised by the
Administrative Agent through any Person who, at the time of the execution of a
particular instrument, is an officer of the Administrative Agent. The power of
attorney conferred by this SECTION 9.03(e) is granted for valuable consideration
and is coupled with an interest and is irrevocable so LONG as the Obligations,
or any part thereof, shall remain unpaid or the Lenders are obligated to make
any Borrowings under the Loan Documents.

     9.04 LIABILITY OF ADMINISTRATIVE AGENT. No Agent-Related Person shall (a)
be liable for any action taken or omitted to be taken by any of them under or in
connection with this Agreement or any other Loan Document or the transactions
contemplated hereby (except for its own gross negligence or willful misconduct
in connection with its duties expressly set forth herein), or (b) be responsible
in any manner to any Lender or participant for any recital, statement,
representation or warranty made by any Loan Party or any officer thereof,
contained herein or in any other Loan Document, or in any certificate, report,
statement or other document referred to or provided for in, or received by the
Administrative Agent under or in connection with, this Agreement or any other
Loan Document, or the validity, effectiveness, genuineness, enforceability or
sufficiency of this Agreement or any other Loan Document, or for the creation,
perfection or priority of any Liens purported to be created by any of the Loan
Documents, or the validity, genuineness, enforceability, existence, value or
sufficiency of any collateral security, or to make any inquiry respecting the
performance by the Borrower of its obligations hereunder or under any other Loan
Document, or for any failure of any Loan Party or any other party to any Loan
Document to perform its obligations hereunder or thereunder. No Agent-Related
Person shall be under any obligation to any Lender or participant to ascertain
or to inquire as to the observance or performance of any of the agreements
contained in, or conditions of, this Agreement or any other Loan Document, or to
inspect the properties, books or records of any Loan Party or any Affiliate
thereof.

     9.05 RELIANCE BY ADMINISTRATIVE AGENT. (a) The Administrative Agent shall
be entitled to rely, and shall be fully protected in relying, upon any writing,
communication, signature, resolution, representation, notice, consent,
certificate, affidavit, letter, telegram, facsimile, telex or telephone message,
statement or other document or conversation believed by it to be genuine and
correct and to have been signed, sent or made by the proper Person or Persons,
and upon advice and statements of legal counsel (including counsel to any Loan
Party), independent accountants and other experts selected by the Administrative
Agent. The Administrative Agent shall be fully justified in failing or refusing
to take any action under any Loan Document unless it shall first receive such
advice or concurrence of the Required Lenders as it deems appropriate and, if it
so requests, it shall first be indemnified to its satisfaction by the Lenders
against any and all liability and expense which may be incurred by it by reason
of taking or continuing to take any such action. The Administrative Agent shall
in all cases be fully protected in acting, or in refraining from acting, under
this Agreement or any other Loan Document in accordance with a request or
consent of the Required Lenders or all the Lenders, if required hereunder, and
such request and any action taken or failure to act pursuant thereto shall be
binding upon all the Lenders and participants. Where this Agreement expressly
permits or prohibits an action unless the Required Lenders

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otherwise determine, the Administrative Agent shall, and in all other instances,
the Administrative Agent may, but shall not be required to, initiate any
solicitation for the consent or a vote of the Lenders.

     (b) For purposes of determining compliance with the conditions specified in
SECTION 4.01, each Lender that has funded its Pro Rata Share of the Borrowing(s)
on the Conditions Effective Date (or, if there is no Borrowing made on such
date, each Lender other than Lenders who gave written objection to the
Administrative Agent prior to such date) shall be deemed to have consented to,
approved or accepted or to be satisfied with, each document or other matter
either sent by the Administrative Agent to such Lender for consent, approval,
acceptance or satisfaction, or required hereunder to be consented to or approved
by or acceptable or satisfactory to a Lender.

     9.06 NOTICE OF DEFAULT. The Administrative Agent shall not be deemed to
have knowledge or notice of the occurrence of any Default or Event of Default,
except with respect to defaults in the payment of principal, interest and fees
required to be paid to the Administrative Agent for the account of the Lenders,
unless the Administrative Agent shall have received written notice from a Lender
or the Borrower referring to this Agreement, describing such Default or Event of
Default and stating that such notice is a "NOTICE OF DEFAULT." The
Administrative Agent will notify the Lenders of its receipt of any such notice.
The Administrative Agent shall take such action with respect to such Default or
Event of Default as may be directed by the Required Lenders in accordance with
ARTICLE VIII; PROVIDED, HOWEVER, that unless and until the Administrative Agent
has received any such direction, the Administrative Agent may (but shall not be
obligated to) take such action, or refrain from taking such action, with respect
to such Default or Event of Default as it shall deem advisable or in the best
interest of the Lenders.

     9.07 CREDIT DECISION; DISCLOSURE OF INFORMATION BY ADMINISTRATIVE AGENT.
Each Lender acknowledges that no Agent-Related Person has made any
representation or warranty to it, and that no act by the Administrative Agent
hereinafter taken, including any consent to and acceptance of any assignment or
review of the affairs of any Loan Party or any Affiliate thereof, shall be
deemed to constitute any representation or warranty by any Agent-Related Person
to any Lender as to any matter, including whether Agent-Related Persons have
disclosed material information in their possession. Each Lender represents to
the Administrative Agent that it has, independently and without reliance upon
any Agent-Related Person and based on such documents and information as it has
deemed appropriate, made its own appraisal of and investigation into the
business, prospects, operations, property, financial and other condition and
creditworthiness of the Loan Parties and their respective Subsidiaries, and all
applicable bank or other regulatory Laws relating to the transactions
contemplated hereby, and made its own decision to enter into this Agreement and
to extend credit to the Borrower hereunder. Each Lender also represents that it
will, independently and without reliance upon any Agent-Related Person and based
on such documents and information as it shall deem appropriate at the time,
continue to make its own credit analysis, appraisals and decisions in taking or
not taking action under this Agreement and the other Loan Documents, and to make
such investigations as it deems necessary to inform itself as to the business,
prospects, operations, property, financial and other condition and
creditworthiness of the Borrower and the other Loan Parties. Except for notices,
reports and other documents expressly required to be furnished to the Lenders by
the Administrative Agent herein, the Administrative Agent shall not have any
duty or responsibility to provide any Lender with any credit or other
information concerning the business, prospects, operations, property, financial
and other condition or creditworthiness of any of the Loan Parties or any of
their respective Affiliates which may come into the possession of any
Agent-Related Person.

     9.08  INDEMNIFICATION OF ADMINISTRATIVE AGENT. Whether or not the
transactions contemplated hereby are consummated, the Lenders shall indemnify
upon demand each Agent-Related Person (to the extent not reimbursed by or on
behalf of any Loan Party and without limiting the obligation

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of any Loan Party to do so), pro rata, and hold harmless each Agent-Related
Person from and against any and all Indemnified Liabilities incurred by it;
PROVIDED, HOWEVER, that no Lender shall be liable for the payment to any
Agent-Related Person of any portion of such Indemnified Liabilities resulting
from such Person's gross negligence or willful misconduct; PROVIDED, HOWEVER,
that no action taken in accordance with the directions of the Required Lenders
shall be deemed to constitute gross negligence or willful misconduct for
purposes of this Section. Without limitation of the foregoing, each Lender shall
reimburse the Administrative Agent upon demand for its ratable share of any
costs or out-of-pocket expenses (including Attorney Costs) incurred by the
Administrative Agent in connection with the preparation, execution, delivery,
administration, modification, amendment or enforcement (whether through
negotiations, legal proceedings or otherwise) of, or legal advice in respect of
rights or responsibilities under, this Agreement, any other Loan Document, or
any document contemplated by or referred to herein, to the extent that the
Administrative Agent is not reimbursed for such expenses by or on behalf of the
Borrower. The undertaking in this Section shall survive termination of the
Commitments, the payment of all Obligations hereunder and the resignation or
replacement of the Administrative Agent.

     9.09 ADMINISTRATIVE AGENT IN ITS INDIVIDUAL CAPACITY. Bank of America and
its Affiliates may make loans to, accept deposits from, acquire equity interests
in and generally engage in any kind of banking, trust, financial advisory,
underwriting or other business with each of the Loan Parties and their
respective Affiliates as though Bank of America were not the Administrative
Agent or the L/C Issuer hereunder and without notice to or consent of the
Lenders. The Lenders acknowledge that, pursuant to such activities, Bank of
America or its Affiliates may receive information regarding any Loan Party or
its Affiliates (including information that may be subject to confidentiality
obligations in favor of such Loan Party or such Affiliate) and acknowledge that
the Administrative Agent shall be under no obligation to provide such
information to them. With respect to its Loans, Bank of America shall have the
same rights and powers under this Agreement as any other Lender and may exercise
such rights and powers as though it were not the Administrative Agent or the L/C
Issuer, and the terms "LENDER" and "LENDERS" include Bank of America in its
individual capacity.

     9.10 SUCCESSOR ADMINISTRATIVE AGENT. The Administrative Agent may resign as
Administrative Agent upon 30 days' notice to the Lenders with a copy of such
notice to the Borrower. If the Administrative Agent resigns under this
Agreement, the Required Lenders shall appoint from among the Lenders a successor
administrative agent for the Lenders which successor administrative agent shall
be consented to by the Borrower at all times other than during the existence of
an Event of Default (which consent of the Borrower shall not be unreasonably
withheld or delayed). If no successor administrative agent is appointed prior to
the effective date of the resignation of the Administrative Agent, the
Administrative Agent may appoint, after consulting with the Lenders and the
Borrower, a successor administrative agent from among the Lenders. Upon the
acceptance of its appointment as successor administrative agent hereunder, such
successor administrative agent shall succeed to all the rights, powers and
duties of the retiring Administrative Agent and the term "ADMINISTRATIVE AGENT"
shall mean such successor administrative agent and the retiring Administrative
Agent's appointment, powers and duties as Administrative Agent shall be
terminated. After any retiring Administrative Agent's resignation hereunder as
Administrative Agent, the provisions of this ARTICLE IX and SECTIONS 10.03 and
10.13 shall inure to its benefit as to any actions taken or omitted to be taken
by it while it was Administrative Agent under this Agreement. If no successor
administrative agent has accepted appointment as Administrative Agent by the
date which is 30 days following a retiring Administrative Agent's notice of
resignation, the retiring Administrative Agent's resignation shall nevertheless
thereupon become effective and the Lenders shall perform all of the duties of
the Administrative Agent hereunder until such time, if any, as the Required
Lenders appoint a successor agent as provided for above.

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     9.11 OTHER AGENTS; LEAD MANAGERS. None of the Lenders or other Persons
identified on the facing page or signature pages of this Agreement as a
"syndication agent," as a "co-documentation agent," any other type of agent
(other than the Administrative Agent), "lead arranger," or "book manager" shall
have any right, power, obligation, liability, responsibility or duty under this
Agreement other than those applicable to all Lenders as such. Without limiting
the foregoing, none of the Lenders so identified shall have or be deemed to have
any fiduciary relationship with any Lender. Each Lender acknowledges that it has
not relied, and will not rely, on any of the Lenders so identified in deciding
to enter into this Agreement or in taking or not taking action hereunder.

                                   ARTICLE X.
                                  MISCELLANEOUS

     10.01 AMENDMENTS, RELEASE OF COLLATERAL, ETC. (a) No amendment or waiver of
any provision of this Agreement or any other Loan Document, and no consent to
any departure by the Borrower or any other Loan Party therefrom, shall be
effective unless in writing signed by the Required Lenders and the Borrower or
the applicable Loan Party, as the case may be, and acknowledged by the
Administrative Agent, and each such waiver or consent shall be effective only in
the specific instance and for the specific purpose for which given; PROVIDED,
HOWEVER, that no such amendment, waiver or consent shall, unless in writing and
signed by each of the Lenders directly affected thereby and by the Borrower, and
acknowledged by the Administrative Agent, do any of the following:

           (i) extend or increase the Commitment of any Lender (or reinstate
     any Commitment terminated pursuant to SECTION 8.02);

           (ii) postpone any date fixed by this Agreement or any other Loan
     Document for any payment or mandatory prepayment of principal, interest,
     fees or other amounts due to the Lenders (or any of them) hereunder or
     under any other Loan Document;

           (iii) reduce the principal of, or the rate of interest specified
     herein on, any Loan or L/C Borrowing or (subject to clause (ii) of the
     proviso below) any fees or other amounts payable hereunder or under any
     other Loan Document, PROVIDED, HOWEVER, that only the consent of the
     Required Lenders shall be necessary to amend the definition of "DEFAULT
     RATE" or to waive any obligation of the Borrower to pay interest at the
     Default Rate;

           (iv) change the percentage of the Aggregate Commitments or of the
     aggregate unpaid principal amount of the Loans and L/C Obligations which is
     required for the Lenders or any of them to take any action hereunder;

           (v) change the Pro Rata Share of any Lender;

           (vi) Release a material amount of Collateral or release any Guarantor
     from a Guaranty (except as otherwise permitted under this SECTION 10.01);
     or

           (vii) amend this Section, or SECTION 2.12, or any provision herein
     providing for unanimous consent or other action by all the Lenders;

and, PROVIDED FURTHER, that (i) no amendment, waiver or consent shall, unless in
writing and signed by the L/C Issuer in addition to the Required Lenders or all
the Lenders, as the case may be, affect the rights or duties of the L/C Issuer
under this Agreement or any Letter of Credit Application relating to any Letter
of Credit issued or to be issued by it; (ii) no amendment, waiver or consent
shall, unless in writing and

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signed by the Administrative Agent in addition to the Required Lenders or all
the Lenders, as the case may be, affect the rights or duties of the
Administrative Agent under this Agreement or any other Loan Document; and (iii)
the Agent/Arranger Fee Letter may be amended, or rights or privileges thereunder
waived, in a writing executed only by the parties thereto. Notwithstanding
anything to the contrary herein, any Lender that has failed to fund any portion
of the Loans or participation in L/C Obligations required to be funded by it
hereunder shall not have any right to approve or disapprove any amendment,
waiver or consent hereunder, except that the Pro Rata Share of such Lender may
not be increased without the consent of such Lender.

     (b) Any amendment to any Loan Document which purports to (i) change the
allocation of payments between the Revolver Facility and the Term Loan Facility,
(ii) decrease the amount of any mandatory prepayment or commitment reduction
required by SECTION 2.04 or (iii) change this SECTION 10.01(b), must be by an
instrument in writing executed by Borrower, the Administrative Agent, the
Required Revolver Lenders, and the Required Term Lenders.

     (c) Upon any sale, transfer, or disposition of Collateral which is
permitted pursuant to the Loan Documents, and upon ten (10) Business Days' prior
written request by the Borrower (which request must be accompanied by (a) true
and correct copies of all material documents of transfer or disposition,
including any contract of sale, (ii) a preliminary closing statement and
instructions to the title company, if any, (iii) all requested release
instruments in form and substance satisfactory to the Administrative Agent) and
(iv) if required, written consent of the requisite Lenders, the Administrative
Agent shall (and is hereby irrevocably authorized by the Lenders to) execute
such documents as may be necessary to evidence the release of Liens granted to
the Administrative Agent for the benefit of the Lenders pursuant hereto in such
Collateral. The Administrative Agent shall not be required to execute any
release instruments on terms which, in the Administrative Agent's opinion, would
expose the Administrative Agent to liability or create any obligation or entail
any consequence other than the release of liens without recourse or warranty. No
such release shall impair the Administrative Agent's lien on the proceeds of
sale of such Collateral.

     (d) If all outstanding Loans and other Obligations have been indefeasibly
paid in full and the Commitments have terminated or have been reduced to zero,
and, subject to SECTION 10.01(e) all Lender Hedging Agreement have terminated,
the Administrative Agent agrees to, and the Lenders hereby instruct the
Administrative Agent to, at the Borrower's expense, execute such releases of the
Collateral Documents as the Borrower shall reasonably request and this Agreement
shall be deemed terminated except that such termination shall not relieve the
Borrower of any obligation to make any payments to the Administrative Agent or
any Lender required by any Loan Document to the extent accruing, or relating to
an event occurring, prior to such termination.

     (e) Notwithstanding any provision herein to the contrary, if the
Commitments have been terminated, and the only outstanding Obligations are
amounts owed pursuant to one or more Lender Hedging Agreements, the
Administrative Agent will, and is hereby authorized to, (A) release the Liens
created under the Loan Documents and (B) release all Guaranties of the Borrower,
provided, that contemporaneously with such release, (i) the Borrower (and, if
applicable, the Subsidiary that is a party to such Lender Hedging Agreements)
(A) executes a margin agreement in form and substance acceptable to such
Lender(s) (or its Affiliates) that are parties to such Lender Hedging Agreements
(the "LENDER COUNTERPARTIES") and (B), if required, provides collateral in the
form of cash or a letter of credit having an aggregate value acceptable to such
Lender Counterparties, and (ii) if such Lender Hedging Agreement is executed by
a Subsidiary of the Borrower and the Borrower and the MLP are not parties
thereto, the Borrower and the MLP execute a guaranty covering such Subsidiary's
obligations thereunder, such

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guaranty to be in form and substance satisfactory to the Lender Counterparties.
Any release under this SECTION 10.01(e) must be in writing and signed by the
Administrative Agent.

     10.02 NOTICES AND OTHER COMMUNICATIONS; FACSIMILE COPIES.

     (a) GENERAL. Unless otherwise expressly provided herein, all notices and
other communications provided for hereunder and under the other Loan Documents
shall be in writing (including by facsimile transmission) and mailed, faxed or
delivered, to the address, facsimile number or (subject to subsection (c) below)
electronic mail address specified for notices on SCHEDULE 10.02 (for the
Borrower, any Guarantor and the Administrative Agent) or on the Administrative
Details Form (for the other Lenders); or, in the case of the Borrower, the
Guarantors, the Administrative Agent, or the L/C Issuer, to such other address
as shall be designated by such party in a notice to the other parties, and in
the case of any other party, to such other address as shall be designated by
such party in a notice to the Borrower, the Administrative Agent and the L/C
Issuer. All such notices and other communications shall be deemed to be given or
made upon the earlier to occur of (i) actual receipt by the intended recipient
and (ii) (A) if delivered by hand or by courier, when signed for by the intended
recipient; (B) if delivered by mail, four Business Days after deposit in the
mails, postage prepaid; (C) if delivered by facsimile, when sent and receipt has
been confirmed by telephone; and (D) if delivered by electronic mail (which form
of delivery is subject to the provisions of subsection (c) below), when
delivered; PROVIDED, HOWEVER, that notices and other communications to the
Administrative Agent or the L/C Issuer pursuant to ARTICLE II shall not be
effective until actually received by such Person. Any notice or other
communication permitted to be given, made or confirmed by telephone hereunder
shall be given, made or confirmed by means of a telephone call to the intended
recipient at the number specified in accordance with this Section, it being
understood and agreed that a voicemail message shall in no event be effective as
a notice, communication or confirmation hereunder.

     (b) EFFECTIVENESS OF FACSIMILE DOCUMENTS AND SIGNATURES. Loan Documents may
be transmitted and/or signed by facsimile. The effectiveness of any such
documents and signatures shall, subject to applicable Law, have the same force
and effect as manually-signed originals and shall be binding on all Loan
Parties, the Administrative Agent and the Lenders. The Administrative Agent may
also require that any such documents and signatures be confirmed by a
manually-signed original thereof; PROVIDED, HOWEVER, that the failure to request
or deliver the same shall not limit the effectiveness of any facsimile document
or signature.

     (c) LIMITED USE OF ELECTRONIC MAIL. Electronic mail and internet and
intranet websites may be used only to distribute routine communications, such as
financial statements and other information, and to distribute Loan Documents for
execution by the parties thereto, and shall not be recognized hereunder for any
other purpose.

     (d) RELIANCE BY ADMINISTRATIVE AGENT AND LENDERS. The Administrative Agent
and the Lenders shall be entitled to rely and act upon any notices (including
telephonic Borrowing Notices) purportedly given by or on behalf of the Borrower
even if (i) such notices were not made in a manner specified herein, were
incomplete or were not preceded or followed by any other form of notice
specified herein, or (ii) the terms thereof, as understood by the recipient,
varied from any confirmation thereof. The Borrower shall indemnify each
Agent-Related Person and each Lender from all losses, costs, expenses and
liabilities resulting from the reliance by such Person on each notice
purportedly given by or on behalf of the Borrower. All telephonic notices to and
other communications with the Administrative Agent may be recorded by the
Administrative Agent, and each of the parties hereto hereby consents to such
recording.

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     10.03 NO WAIVER; CUMULATIVE REMEDIES. No failure by any Lender or the
Administrative Agent to exercise, and no delay by any such Person in exercising,
any right, remedy, power or privilege hereunder shall operate as a waiver
thereof; nor shall any single or partial exercise of any right, remedy, power or
privilege hereunder preclude any other or further exercise thereof or the
exercise of any other right, remedy, power or privilege. The rights, remedies,
powers and privileges herein or therein provided are cumulative and not
exclusive of any rights, remedies, powers and privileges provided by law.

     10.04 ATTORNEY COSTS; EXPENSES AND TAXES. The Borrower agrees (a) to pay or
reimburse the Administrative Agent for all costs and expenses incurred in
connection with the development, preparation, negotiation, syndication,
administration and execution of this Agreement and the other Loan Documents,
including the filing, recording, refiling or rerecording of any Mortgage, any
pledge agreement and any Security Agreement and/or any Uniform Commercial Code
financing statements relating thereto and all amendments, supplements and
modifications to any thereof and any and all other documents or instruments of
further assurance required to be filed or recorded or refiled or rerecorded by
the terms hereof or of any mortgage, any pledge agreement or any security
agreement, and any amendment, waiver, consent or other modification of the
provisions hereof and thereof (whether or not the transactions contemplated
hereby or thereby are consummated), and the consummation and administration of
the transactions contemplated hereby and thereby, including all Attorney Costs,
and (b) to pay or reimburse the Administrative Agent and each Lender for all
costs and expenses incurred in connection with the enforcement, attempted
enforcement, or preservation of any rights or remedies under this Agreement or
the other Loan Documents (including all such costs and expenses incurred during
any workout or restructuring in respect of the Obligations and during any legal
proceeding, including any proceeding under any Debtor Relief Law), including all
Attorney Costs. The foregoing costs and expenses shall include all search,
filing, recording, title insurance and appraisal charges and fees and taxes
related thereto, and other out-of-pocket expenses incurred by the Administrative
Agent and the cost of independent public accountants and other outside experts
retained by the Administrative Agent or any Lender. The agreements in this
Section shall survive the termination of the Commitments and repayment of all
the other Obligations.

     10.05 INDEMNIFICATION. Whether or not the transactions contemplated hereby
are consummated, each of the Borrower, the MLP and each other Guarantor (by
execution of a Guaranty), jointly and severally, agrees to indemnify, save and
hold harmless each Agent-Related Person, each Arranger, each Lender, the L/C
Issuer and their respective Affiliates, directors, officers, employees, counsel,
agents and attorneys-in-fact (collectively the "INDEMNITEES") from and against:
(a) any and all claims, demands, actions or causes of action that are asserted
against any Indemnitee by any Person (other than the Administrative Agent or any
Lender) relating directly or indirectly to a claim, demand, action or cause of
action that such Person asserts or may assert against any Loan Party, any
Affiliate of any Loan Party or any of their respective officers or directors,
arising out of or relating to, the Loan Documents, the Commitments, the use or
contemplated use of the proceeds of any Loans, or the relationship of any Loan
Party, the Administrative Agent, the Lenders and the L/C Issuer under this
Agreement or any other Loan Document; (b) any and all claims, demands, actions
or causes of action that may at any time (including at any time following
repayment of the Obligations and the resignation of the Administrative Agent or
the replacement of any Lender) be asserted or imposed against any Indemnitee,
arising out of or relating to, the Loan Documents, the Commitments, the use or
contemplated use of the proceeds of any Loans, or the relationship of any Loan
Party, the Administrative Agent, the Lenders and the L/C Issuer under this
Agreement or any other Loan Document; (c) without limiting the foregoing, any
and all claims, demands, actions or causes of action, judgments and orders,
penalties and fines that are asserted or imposed against any Indemnitee, (i)
under the application of any Environmental Law applicable to the Borrower or any
of its Subsidiaries or any of their properties or assets, including the
treatment or disposal of Hazardous Substances on any of their properties or
assets, (ii) as a result of the breach or non-compliance by the

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Borrower or any Subsidiary with any Environmental Law applicable to the Borrower
or any Subsidiary, (iii) due to past ownership by the Borrower or any Subsidiary
of any of their properties or assets or past activity on any of their properties
or assets which, though lawful and fully permissible at the time, could result
in present liability, (iv) due to the presence, use, storage, treatment or
disposal of Hazardous Substances on or under, or the escape, seepage, leakage,
spillage, discharge, emission or Release from, any of the properties owned or
operated by the Borrower or any Subsidiary (including any liability asserted or
arising under any Environmental Law), regardless of whether caused by, or within
the control of, the Borrower or such Subsidiary, or (v) due to any other
environmental, health or safety condition in connection with the Loan Documents;
(d) any administrative or investigative proceeding by any Governmental Authority
arising out of or related to a claim, demand, action or cause of action
described in subsection (a), (b) or (c) above; and (e) any and all liabilities
(including liabilities under indemnities), losses, costs or expenses (including
Attorney Costs and settlement costs) that any Indemnitee suffers or incurs as a
result of the assertion of any foregoing claim, demand, action, cause of action
or proceeding, or as a result of the preparation of any defense in connection
with any foregoing claim, demand, action, cause of action or proceeding, in all
cases, WHETHER OR NOT ARISING OUT OF THE STRICT LIABILITY OR NEGLIGENCE OF AN
INDEMNITEE, and whether or not an Indemnitee is a party to such claim, demand,
action, cause of action or proceeding (all the foregoing, collectively, the
"INDEMNIFIED LIABILITIES"); PROVIDED that no Indemnitee shall be entitled to
indemnification for any claim to the extent caused by its own gross negligence
or willful misconduct. The agreements in this Section shall survive and continue
for the benefit of the indemnitees at all times after the Borrower's acceptance
of the Lenders' commitments for the Senior Credit Facility, whether or not the
Conditions Effective Date shall occur and shall survive the termination of the
Commitments and repayment of all the other Obligations.

     10.06 PAYMENTS SET ASIDE. To the extent that the Borrower makes a payment
to the Administrative Agent or any Lender, or the Administrative Agent or any
Lender exercises its right of set-off, and such payment or the proceeds of such
set-off or any part thereof is subsequently invalidated, declared to be
fraudulent or preferential, set aside or required (including pursuant to any
settlement entered into by the Administrative Agent or such Lender in its
discretion) to be repaid to a trustee, receiver or any other party, in
connection with any proceeding under any Debtor Relief Law or otherwise, then
(a) to the extent of such recovery, the obligation or part thereof originally
intended to be satisfied shall be revived and continued in full force and effect
as if such payment had not been made or such set-off had not occurred, and (b)
each Lender severally agrees to pay to the Administrative Agent upon demand its
applicable share of any amount so recovered from or repaid by the Administrative
Agent, plus interest thereon from the date of such demand to the date such
payment is made at a rate per annum equal to the Federal Funds Rate from time to
time in effect.

     10.07 SUCCESSORS AND ASSIGNS.

     (a) The provisions of this Agreement shall be binding upon and inure to the
benefit of the parties hereto and their respective successors and assigns
permitted hereby, except that neither the Borrower nor the MLP may assign or
otherwise transfer any of its rights or obligations hereunder without the prior
written consent of each Lender and no Lender may assign or otherwise transfer
any of its rights or obligations hereunder except (i) to an Eligible Assignee in
accordance with the provisions of paragraph (b) of this Section, (ii) by way of
participation in accordance with the provisions of paragraph (d) of this Section
or (iii) by way of pledge or assignment of a security interest subject to the
restrictions of paragraph (f) of this Section (and any other attempted
assignment or transfer by any party hereto shall be null and void). Nothing in
this Agreement, expressed or implied, shall be construed to confer upon any
Person (other than the parties hereto, their respective successors and assigns
permitted hereby, Participants to the extent provided in paragraph (d) of this
Section and, to the extent expressly

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contemplated hereby, the Related Parties of each of the Administrative Agent and
the Lenders) any legal or equitable right, remedy or claim under or by reason of
this Agreement.

     (b) Any Lender may at any time assign to one or more Eligible Assignees all
or a portion of its rights and obligations under this Agreement (including all
or a portion of its Commitment and the Loans (including for purposes of this
subsection (b), participations in L/C Obligations) at the time owing to it);
PROVIDED that (i) except in the case of an assignment of the entire remaining
amount of the assigning Lender's Commitment and the Loans at the time owing to
it or in the case of an assignment to a Lender or an Affiliate of a Lender or an
Approved Fund with respect to a Lender, the aggregate amount of the Commitment
(which for this purpose includes Loans outstanding thereunder) or, if the
applicable Commitment is not then in effect, the outstanding principal balance
of the Loan of the assigning Lender subject to each such assignment (determined
as of the date the Assignment and Assumption with respect to such assignment is
delivered to the Administrative Agent or, if "TRADE DATE" is specified in the
Assignment and Assumption, as of the Trade Date) shall not be less than
$5,000,000, in the case of any assignment in respect of a Loan under the
Revolver Facility, or $1,000,000 in the case of any assignment of a Loan under
the Term Loan Facility, unless each of the Administrative Agent and, so long as
no Default has occurred and is continuing, the Borrower otherwise consent (each
such consent not to be unreasonably withheld or delayed); (ii) each partial
assignment shall be made as an assignment of a proportionate part of all the
assigning Lender's rights and obligations under this Agreement with respect to
the Loan or the Commitment assigned, except that this clause (ii) shall not
prohibit any Lender from assigning all or a portion of its rights and
obligations as between the Term Loan Facility and the Revolver Facility on a
non-pro rata basis, and (iii) the parties to each assignment shall execute and
deliver to the Administrative Agent an Assignment and Assumption, together with
a processing and recordation fee of $3,500, and the Eligible Assignee, if it
shall not be a Lender, shall deliver to the Administrative Agent an
Administrative Details Form. Subject to acceptance and recording thereof by the
Administrative Agent pursuant to paragraph (c) of this Section, from and after
the effective date specified in each Assignment and Assumption, the Eligible
Assignee thereunder shall be a party to this Agreement and, to the extent of the
interest assigned by such Assignment and Assumption, have the rights and
obligations of a Lender under this Agreement, and the assigning Lender
thereunder shall, to the extent of the interest assigned by such Assignment and
Assumption, be released from its obligations under this Agreement (and, in the
case of an Assignment and Assumption covering all of the assigning Lender's
rights and obligations under this Agreement, such Lender shall cease to be a
party hereto) but shall continue to be entitled to the benefits of SECTIONS
3.07, 10.04 and 10.05 with respect to facts and circumstances occurring prior to
the effective date of such assignment. Any assignment or transfer by a Lender of
rights or obligations under this Agreement that does not comply with this
paragraph shall be treated for purposes of this Agreement as a sale by such
Lender of a participation in such rights and obligations in accordance with
paragraph (d) of this Section.

     (c) The Administrative Agent, acting solely for this purpose as an agent of
the Borrower, shall maintain at one of its offices a copy of each Assignment and
Assumption delivered to it and a register for the recordation of the names and
addresses of the Lenders, and the Commitments of, and principal amounts of the
Loans and L/C Obligations owing to, each Lender pursuant to the terms hereof
from time to time (the "REGISTER"). The entries in the Register shall be
conclusive absent manifest error, and the Borrower, the Administrative Agent and
the Lenders may treat each Person whose name is recorded in the Register
pursuant to the terms hereof as a Lender hereunder for all purposes of this
Agreement, notwithstanding notice to the contrary. The Register shall be
available for inspection by the Borrower and any Lender, at any reasonable time
and from time to time upon reasonable prior notice.

     (d) Any Lender may at any time, without the consent of, or notice to, the
Borrower or the Administrative Agent, sell participations to any Person (other
than a natural person or the Borrower or

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any of the Borrower's Affiliates or Subsidiaries) (each, a "PARTICIPANT") in all
or a portion of such Lender's rights and/or obligations under this Agreement
(including all or a portion of its Commitment and/or the Loans (including such
Lender's participation in L/C Obligations) owing to it); PROVIDED that (i) such
Lender's obligations under this Agreement shall remain unchanged, (ii) such
Lender shall remain solely responsible to the other parties hereto for the
performance of such obligations and (iii) the Borrower, the Administrative Agent
and the other Lenders shall continue to deal solely and directly with such
Lender in connection with such Lender's rights and obligations under this
Agreement. Any agreement or instrument pursuant to which a Lender sells such a
participation shall provide that such Lender shall retain the sole right to
enforce this Agreement and to approve any amendment, modification or waiver of
any provision of this Agreement; PROVIDED that such agreement or instrument may
provide that such Lender will not, without the consent of the Participant, agree
to any amendment, modification or waiver that would (i) postpone any date upon
which any payment of money is scheduled to be paid to such Participant, (ii)
reduce the principal, interest, fees or other amounts payable to such
Participant, or (iii) release the MLP from its Guaranty. Subject to subsection
(e) of this Section, the Borrower agrees that each Participant shall be entitled
to the benefits of SECTIONS 3.01, 3.04 and 3.05 to the same extent as if it were
a Lender and had acquired its interest by assignment pursuant to subsection (b)
of this Section. To the extent permitted by law, each Participant also shall be
entitled to the benefits of SECTION 10.09 as though it were a Lender, PROVIDED
such Participant agrees to be subject to SECTION 2.12 as though it were a
Lender.

     (e) A Participant shall not be entitled to receive any greater payment
under SECTION 3.01 or 3.04 than the applicable Lender would have been entitled
to receive with respect to the participation sold to such Participant, unless
the sale of the participation to such Participant is made with the Borrower's
prior written consent. A Participant that would be a Foreign Lender if it were a
Lender shall not be entitled to the benefits of SECTION 3.01 unless the Borrower
is notified of the participation sold to such Participant and such Participant
agrees, for the benefit of the Borrower, to comply with SECTION 10.15 as though
it were a Lender.

     (f) Any Lender may at any time pledge or assign a security interest in all
or any portion of its rights under this Agreement (including under its Notes, if
any) to secure obligations of such Lender, including any pledge or assignment to
secure obligations to a Federal Reserve Bank; PROVIDED THAT no such pledge or
assignment shall release a Lender from any of its obligations hereunder or
substitute any such pledgee or assignee for such Lender as a party hereto.

     (g) If the consent of the Borrower to an assignment or to an Eligible
Assignee is required hereunder (including a consent to an assignment which does
not meet the minimum assignment threshold specified in clause (i) of the proviso
to the first sentence of SECTION 10.07(b)), the Borrower shall be deemed to have
given its consent five Business Days after the date notice thereof has been
delivered by the assigning Lender (through the Administrative Agent) unless such
consent is expressly refused by the Borrower prior to such fifth Business Day.

     (h) Notwithstanding anything to the contrary contained herein, if at any
time Bank of America assigns all of its Commitment and Loans pursuant to
subsection (b) above, Bank of America may, (i) upon 30 days' notice to the
Borrower and the Lenders, resign as L/C Issuer. In the event of any such
resignation as L/C Issuer, the Borrower shall be entitled to appoint from among
the Lenders a successor L/C Issuer hereunder; PROVIDED, HOWEVER, that no failure
by the Borrower to appoint any such successor shall affect the resignation of
Bank of America as L/C Issuer. Bank of America shall retain all the rights and
obligations of the L/C Issuer hereunder with respect to all Letters of Credit
outstanding as of the effective date of its resignation as L/C Issuer and all
L/C Obligations with respect thereto

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(including the right to require the Lenders to make Base Rate Loans or fund
participations in Unreimbursed Amounts pursuant to SECTION 2.14(c)).

     10.08 CONFIDENTIALITY. Each Lender agrees that it will not disclose without
the prior consent of the Borrower (other than to directors, officers, employees,
auditors, accountants, counsel or other professional advisors of the
Administrative Agent or any Lender) any information with respect to the Borrower
or its Subsidiaries, which is furnished pursuant to this Agreement and which (i)
the Borrower in good faith considers to be confidential and (ii) is either
clearly marked confidential or is designated by the Borrower to the
Administrative Agent or the Lenders in writing as confidential, provided that
any Lender may disclose any such information (a) as has become generally
available to the public, (b) as may be required or appropriate in any report,
statement or testimony submitted to or required by any municipal, state or
federal regulatory body having or claiming to have jurisdiction over such Lender
or submitted to or required by the Board or the Federal Deposit Insurance
Corporation or similar organizations (whether in the United States of America or
elsewhere) or their successors, (c) as may be required or appropriate in
response to any summons or subpoena in connection with any litigation, (d) in
order to comply with any law, order, regulation or ruling applicable to such
Lender, (e) to any Eligible Assignee of or Participant in, or any prospective
Eligible Assignee of or Participant in, any of its rights or obligations under
this Agreement, provided that such Eligible Assignee or Participant or
prospective Eligible Assignee or Participant executes an agreement containing
provisions substantially similar to those contained in this SECTION 10.08, (f)
in connection with the exercise of any remedy by such Lender following an Event
of Default pertaining to the Loan Documents, (g) in connection with any
litigation involving such Lender pertaining to the Loan Documents, (h) to any
Lender or the Administrative Agent, or (i) to any Affiliate of any Lender (it
being understood that the Persons to whom such disclosure is made will be
informed of the confidential nature of such information and obligated to keep
such information confidential).

     10.09 SET-OFF. In addition to any rights and remedies of the Lenders
provided by law, upon the occurrence and during the continuance of any Event of
Default, each Lender is authorized at any time and from time to time, without
prior notice to the Borrower or any other Loan Party, any such notice being
waived by the Borrower (on its own behalf and on behalf of each Loan Party) to
the fullest extent permitted by law, to set off and apply any and all deposits
(general or special, time or demand, provisional or final) at any time held by,
and other indebtedness at any time owing by, such Lender to or for the credit or
the account of the respective Loan Parties against any and all Obligations owing
to the Administrative Agent and the Lenders, now or hereafter existing,
irrespective of whether or not the Administrative Agent or such Lender shall
have made demand under this Agreement or any other Loan Document and although
such Obligations may be contingent or unmatured. Each Lender agrees promptly to
notify the Borrower and the Administrative Agent after any such set-off and
application made by such Lender; PROVIDED, HOWEVER, that the failure to give
such notice shall not affect the validity of such set-off and application.

     10.10 INTEREST RATE LIMITATION. Regardless of any provision contained in
any Loan Document, neither the Administrative Agent nor any Lender shall ever be
entitled to contract for, charge, take, reserve, receive, or apply, as interest
on all or any part of the Obligations, any amount in excess of the Maximum Rate,
and, if any Lender ever does so, then such excess shall be deemed a partial
prepayment of principal and treated hereunder as such and any remaining excess
shall be refunded to the Borrower. In determining if the interest paid or
payable exceeds the Maximum Rate, the Borrower and the Lenders shall, to the
maximum extent permitted under applicable Law, (a) treat all Borrowings as but a
single extension of credit (and the Lenders and the Borrower agree that such is
the case and that provision herein for multiple Borrowings is for convenience
only), (b) characterize any nonprincipal payment as an expense, fee, or premium
rather than as interest, (c) exclude voluntary prepayments and the effects
thereof, and (d) amortize, prorate, allocate, and spread the total amount of
interest throughout the

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entire contemplated term of the Obligations. However, if the Obligations are
paid and performed in full prior to the end of the full contemplated term
thereof, and if the interest received for the actual period of existence thereof
exceeds the Maximum Amount, the Lenders shall refund such excess, and, in such
event, the Lenders shall not, to the extent permitted by Law, be subject to any
penalties provided by any Laws for contracting for, charging, taking, reserving,
or receiving interest in excess of the Maximum Amount. To the extent the Laws of
the State of Texas are applicable for purposes of determining the "MAXIMUM RATE"
or the "MAXIMUM AMOUNT," then those terms mean the "WEEKLY CEILING" from time to
time in effect under Texas Finance Code Section 303.001, as limited by Texas
Finance Code Section 303.009. The Borrower agrees that Chapter 346 of the Texas
Finance Code, as amended (which regulates certain revolving credit loan accounts
and revolving tri-party accounts), does not apply to the Obligations.

     10.11 COUNTERPARTS. This Agreement may be executed in one or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

     10.12 INTEGRATION. This Agreement, together with the other Loan Documents,
comprises the complete and integrated agreement of the parties on the subject
matter hereof and thereof and supersedes all prior agreements, written or oral,
on such subject matter. In the event of any conflict between the provisions of
this Agreement and those of any other Loan Document, the provisions of this
Agreement shall control; PROVIDED THAT the inclusion of supplemental rights or
remedies in favor of the Administrative Agent or the Lenders in any other Loan
Document shall not be deemed a conflict with this Agreement. Each Loan Document
was drafted with the joint participation of the respective parties thereto and
shall be construed neither against nor in favor of any party, but rather in
accordance with the fair meaning thereof.

     10.13 SURVIVAL OF REPRESENTATIONS AND WARRANTIES. All representations and
warranties made hereunder and in any other Loan Document or other document
delivered pursuant hereto or thereto or in connection herewith or therewith
shall survive the execution and delivery hereof and thereof. Such
representations and warranties have been or will be relied upon by the
Administrative Agent and each Lender, regardless of any investigation made by
the Administrative Agent or any Lender or on their behalf and notwithstanding
that the Administrative Agent or any Lender may have had notice or knowledge of
any Default or Event of Default at the time of any Borrowing, and shall continue
in full force and effect as long as any Loan or any other Obligation shall
remain unpaid or unsatisfied.

     10.14 SEVERABILITY. Any provision of this Agreement and the other Loan
Documents to which the Borrower is a party that 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 thereof, and any such prohibition or unenforceability in any
jurisdiction shall not invalidate or render unenforceable such provision in any
other jurisdiction.

     10.15 FOREIGN LENDERS. Each Lender that is a "foreign corporation,
partnership or trust" within the meaning of the Code (a "FOREIGN LENDER") shall
deliver to the Administrative Agent, prior to receipt of any payment subject to
withholding under the Code (or after accepting an assignment of an interest
herein), two duly signed completed copies of either IRS Form W-8BEN or any
successor thereto (relating to such Person and entitling it to an exemption
from, or reduction of, withholding tax on all payments to be made to such Person
by the Borrower pursuant to this Agreement) or IRS Form W-8ECI or any successor
thereto (relating to all payments to be made to such Person by the Borrower
pursuant to this Agreement) or such other evidence satisfactory to the Borrower
and the Administrative Agent that such Person is entitled to an exemption from,
or reduction of, U.S. withholding tax. Thereafter and from time to time, each
such Person shall (a) promptly submit to the Administrative Agent such
additional duly completed and signed copies of one of such forms (or such
successor forms as shall be adopted from time

                                       76
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to time by the relevant United States taxing authorities) as may then be
available under then current United States laws and regulations to avoid, or
such evidence as is satisfactory to the Borrower and the Administrative Agent of
any available exemption from or reduction of, United States withholding taxes in
respect of all payments to be made to such Person by the Borrower pursuant to
this Agreement, (b) promptly notify the Administrative Agent of any change in
circumstances which would modify or render invalid any claimed exemption or
reduction, and (c) take such steps as shall not be materially disadvantageous to
it, in the reasonable judgment of such Lender, and as may be reasonably
necessary (including the re-designation of its Lending Office) to avoid any
requirement of applicable Laws that the Borrower make any deduction or
withholding for taxes from amounts payable to such Person. If such Person fails
to deliver the above forms or other documentation, then the Administrative Agent
may withhold from any interest payment to such Person an amount equivalent to
the applicable withholding tax imposed by Sections 1441 and 1442 of the Code,
without reduction. If any Governmental Authority asserts that the Administrative
Agent did not properly withhold any tax or other amount from payments made in
respect of such Person, such Person shall indemnify the Administrative Agent
therefor, including all penalties and interest, any taxes imposed by any
jurisdiction on the amounts payable to the Agent under this Section, and costs
and expenses (including Attorney Costs) of the Administrative Agent. The
obligation of the Lenders under this Section shall survive the payment of all
Obligations and the resignation or replacement of the Administrative Agent.

     10.16 GOVERNING LAW.

     (a) THIS AGREEMENT SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH,
the LAW OF THE STATE OF TEXAS APPLICABLE TO AGREEMENTS MADE AND TO BE PERFORMED
ENTIRELY WITHIN SUCH STATE; PROVIDED THAT THE ADMINISTRATIVE AGENT AND EACH
LENDER SHALL RETAIN ALL RIGHTS ARISING UNDER UNITED STATES FEDERAL LAW.

     (b) EACH COMPANY AND OTHER PARTY HERETO, AND EACH GUARANTOR, BY EXECUTION
OF A GUARANTY, AGREES AS TO THIS SECTION 10.16(b). ANY LEGAL ACTION OR
PROCEEDING WITH RESPECT TO THIS AGREEMENT OR ANY OTHER LOAN DOCUMENT MAY BE
BROUGHT IN THE COURTS OF THE STATE OF TEXAS SITTING IN HARRIS COUNTY OR OF THE
UNITED STATES FOR THE SOUTHERN DISTRICT OF SUCH STATE, AND BY EXECUTION AND
DELIVERY OF THIS AGREEMENT, THE BORROWER, THE ADMINISTRATIVE Agent AND EACH
LENDER CONSENTS, AND BY EXECUTION OF A GUARANTY, EACH GUARANTOR CONSENTS, FOR
ITSELF AND IN RESPECT OF ITS PROPERTY, TO THE NON-EXCLUSIVE JURISDICTION OF
THOSE COURTS. THE BORROWER, EACH GUARANTOR, THE ADMINISTRATIVE Agent AND EACH
LENDER (1) IRREVOCABLY WAIVES ANY OBJECTION, INCLUDING ANY OBJECTION TO THE
LAYING OF VENUE OR BASED ON THE GROUNDS OF FORUM NON CONVENIENS, WHICH IT MAY
NOW OR HEREAFTER HAVE TO THE BRINGING OF ANY ACTION OR PROCEEDING IN SUCH
JURISDICTION IN RESPECT OF ANY LOAN DOCUMENT OR OTHER DOCUMENT RELATED THERETO,
AND (2) IRREVOCABLY CONSENTS TO THE SERVICE OF PROCESS OUT OF ANY OF THE
AFOREMENTIONED COURTS IN ANY SUCH ACTION OR PROCEEDING BY THE MAILING OF COPIES
THEREOF BY CERTIFIED MAIL, RETURN RECEIPT REQUESTED, POSTAGE PREPAID, AT ITS
ADDRESS FOR NOTICES DESIGNATED HEREIN. THE BORROWER, EACH GUARANTOR, THE
ADMINISTRATIVE Agent AND EACH LENDER WAIVES PERSONAL SERVICE OF ANY SUMMONS,
COMPLAINT OR OTHER PROCESS, WHICH MAY BE MADE BY ANY OTHER MEANS PERMITTED BY
THE LAW OF SUCH STATE. THE BORROWER AND EACH GUARANTOR, BY ITS EXECUTION OF A
GUARANTY, HEREBY IRREVOCABLY APPOINTS CT CORPORATION SYSTEM, WITH AN ADDRESS AT
350 N. ST.

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PAUL STREET, DALLAS, TEXAS 75201 (THE "TEXAS PROCESS AGENT") AS PROCESS AGENT IN
ITS NAME, PLACE AND STEAD TO RECEIVE AND FORWARD SERVICE OF ANY AND ALL WRITS,
SUMMONSES AND OTHER LEGAL PROCESS IN ANY SUIT, ACTION OR PROCEEDING BROUGHT IN
THE STATE OF TEXAS, AGREES THAT SUCH SERVICE IN ANY SUCH SUIT, ACTION OR
PROCEEDING MAY BE MADE UPON THE TEXAS PROCESS AGENT, AND AGREES TO TAKE ALL SUCH
ACTION AS MAY BE NECESSARY TO CONTINUE SAID APPOINTMENT IN FULL FORCE AND
EFFECT.

     10.17 WAIVER OF RIGHT TO TRIAL BY JURY, ETC. EACH PARTY TO THIS AGREEMENT
AND EACH GUARANTOR, BY EXECUTION OF A GUARANTY, HEREBY (a) EXPRESSLY AND
IRREVOCABLY WAIVES ANY RIGHT TO TRIAL BY JURY OF ANY CLAIM, DEMAND, ACTION OR
CAUSE OF ACTION ARISING UNDER ANY LOAN DOCUMENT OR IN ANY WAY CONNECTED WITH OR
RELATED OR INCIDENTAL TO THE DEALINGS OF THE PARTIES TO THE LOAN DOCUMENTS OR
ANY OF THEM WITH RESPECT TO ANY LOAN DOCUMENT, OR THE TRANSACTIONS RELATED
THERETO, IN EACH CASE WHETHER NOW EXISTING OR HEREAFTER ARISING, AND WHETHER
FOUNDED IN CONTRACT OR TORT OR OTHERWISE; AND EACH PARTY HEREBY AGREES AND
CONSENTS THAT ANY SUCH CLAIM, DEMAND, ACTION OR CAUSE OF ACTION SHALL BE DECIDED
BY COURT TRIAL WITHOUT A JURY, AND THAT ANY PARTY TO THIS AGREEMENT MAY FILE AN
ORIGINAL COUNTERPART OR A COPY OF THIS SECTION WITH ANY COURT AS WRITTEN
EVIDENCE OF THE CONSENT OF THE COMPANIES TO THE WAIVER OF THEIR RIGHT TO TRIAL
BY JURY; AND (b) EXPRESSLY AND IRREVOCABLY WAIVES, TO THE MAXIMUM EXTENT NOT
PROHIBITED BY LAW, ANY RIGHT IT MAY HAVE TO CLAIM OR RECOVER IN ANY SUCH ACTION
ANY SPECIAL, EXEMPLARY, PUNITIVE OR CONSEQUENTIAL DAMAGES, OR DAMAGES OTHER
THAN, OR IN ADDITION TO, ACTUAL DAMAGES, PROVIDED THAT THE WAIVER CONTAINED IN
THIS SECTION 10.17(b) SHALL NOT APPLY TO THE EXTENT THAT THE PARTY AGAINST WHOM
DAMAGES ARE SOUGHT HAS ENGAGED IN GROSS NEGLIGENCE OR WILLFUL MISCONDUCT.

     10.18 AGREEMENT REGARDING COLLATERAL. The Lenders hereby authorize the
Administrative Agent to enter into the Agreement Regarding Collateral and each
Lender agrees to be bound by all of the terms and provisions of the Agreement
Regarding Collateral to the same extent as if it were a signatory thereto.

     10.19 NO GENERAL PARTNER'S LIABILITY. The Administrative Agent and the
Lenders agree for themselves and their respective successors and assigns,
including any subsequent holder of any Note, that no claim under this Agreement,
under the Guaranty executed on behalf of the MLP, or under any other Loan
Document shall be made against the General Partner, and that no judgment, order
or execution entered in any suit, action or proceeding, whether legal or
equitable, hereunder, on such Guaranty, or on any other Loan Document shall be
obtained or enforced, against the General Partner or its assets for the purpose
of obtaining satisfaction and payment of amounts owed under this Agreement, such
Guaranty or any other Loan Document. Nothing in this SECTION 10.19, however,
shall be construed so as to prevent the Administrative Agent, any Lender or any
other holder of any Note from commencing any action, suit or proceeding with
respect to or causing legal papers to be served upon the General Partner for the
sole purpose of obtaining jurisdiction over the MLP.

     10.20 ENTIRE AGREEMENT. THIS AGREEMENT AND THE OTHER LOAN DOCUMENTS
REPRESENT THE FINAL AGREEMENT BETWEEN THE PARTIES AND MAY NOT BE CONTRADICTED BY
EVIDENCE OF PRIOR, CONTEMPORANEOUS, OR

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SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES. THERE ARE NO UNWRITTEN ORAL
AGREEMENTS BETWEEN THE PARTIES.


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                         SIGNATURES BEGIN ON NEXT PAGE]

                                       79
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     IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
duly executed as of the date first above written.

                          MARKWEST ENERGY OPERATING COMPANY,
                          L.L.C., a Delaware limited liability company, as
                          Borrower

                               By: MarkWest Energy Partners, L.P.
                                   its sole Member

                               By: MarkWest Energy GP, L.L.C.,
                                   its General Partner


                               By: /s/ Gerald A. Tywoniuk
                                   -------------------------------------------
                               Name:   Gerald A. Tywoniuk
                               Title:  Senior Vice President, Finance
                                       and Chief Financial Officer


                          MARKWEST ENERGY PARTNERS,  L.P., a Delaware limited
                          partnership, as a Guarantor

                               By: MarkWest Energy GP, L.L.C.,
                                   its General Partner


                               By: /s/ Gerald A. Tywoniuk
                                   -------------------------------------------
                               Name:   Gerald A. Tywoniuk
                               Title:  Senior Vice President, Finance
                                       and Chief Financial Officer


                        [THIS IS A SIGNATURE PAGE TO THE
           MARKWEST ENERGY OPERATING COMPANY, L.L.C. CREDIT AGREEMENT]

<Page>

                          BANK OF AMERICA,  N.A., as Administrative Agent and
                          a Lender


                          By:      /s/ Richard L. Stein
                             ---------------------------------------------------
                             Name: Richard L. Stein
                             Title: Principal


                        [THIS IS A SIGNATURE PAGE TO THE
           MARKWEST ENERGY OPERATING COMPANY, L.L.C. CREDIT AGREEMENT]


<Page>

                            FORTIS CAPITAL CORP., as a Lender


                            By: /s/ Darrell W. Holly
                              --------------------------------------------------
                              Name:   Darrell W. Holly
                              Title:  Managing Director

                            By: /s/ David L. Montgomery
                              --------------------------------------------------
                              Name:   David L. Montgomery
                              Title:  Vice President


                        [THIS IS A SIGNATURE PAGE TO THE
           MARKWEST ENERGY OPERATING COMPANY, L.L.C. CREDIT AGREEMENT]

<Page>

                             WELLS FARGO BANK, N.A. as a Lender


                             By: /s/ Todd Stornetta
                                ------------------------------------------------
                              Name:   Todd Stornetta
                              Title:  Vice President


                        [THIS IS A SIGNATURE PAGE TO THE
           MARKWEST ENERGY OPERATING COMPANY, L.L.C. CREDIT AGREEMENT]

<Page>

                          U. S. BANK, NATIONAL ASSOCIATION, as a Lender


                          By:      /s/ Monte E. Deckerd
                             ---------------------------------------------------
                             Name:   Monte E. Deckerd
                              Title: Vice President


                        [THIS IS A SIGNATURE PAGE TO THE
           MARKWEST ENERGY OPERATING COMPANY, L.L.C. CREDIT AGREEMENT]

<Page>

                              ROYAL BANK OF CANADA, as a Lender

                              By: /s/ Lorne Gartner
                                 -----------------------------------------------
                                 Name:   Lorne Gartner
                                 Title:  Vice President


                        [THIS IS A SIGNATURE PAGE TO THE
           MARKWEST ENERGY OPERATING COMPANY, L.L.C. CREDIT AGREEMENT]

<Page>

                           BANK OF OKLAHAMA, N.A., as a Lender

                           By: /s/ Thomas M. Fonlannon
                             ---------------------------------------------------
                             Name:     Thomas M. Fonlannon
                             Title:    Senior Vice President


                        [THIS IS A SIGNATURE PAGE TO THE
           MARKWEST ENERGY OPERATING COMPANY, L.L.C. CREDIT AGREEMENT]