Document:

FIRST AMENDMENT TO

FOURTH AMENDED AND RESTATED CREDIT AGREEMENT  

        THIS FIRST AMENDMENT TO FOURTH AMENDED AND RESTATED CREDIT AGREEMENT (this "Amendment") is entered into as of
March 29, 2002, among MARKWEST HYDROCARBON, INC., a Delaware corporation (the "Borrower"), the undersigned Guarantors (the
"Guarantors"), BANK OF AMERICA, N.A., as Administrative Agent (the "Administrative
Agent") for the Lenders parties to the hereinafter defined Credit Agreement, and the undersigned Lenders. 

        Reference
is made to the Fourth Amended and Restated Credit Agreement dated as of October 12, 2001 (the "Credit Agreement") among
Borrower, Administrative Agent, and the Lenders parties thereto. Unless otherwise defined in this Amendment, capitalized terms used herein shall have the meaning set forth in the Credit Agreement; all
section and schedule references herein are to sections and schedules in the Credit Agreement; and all paragraph references herein are to paragraphs in this Amendment. 

RECITALS  

        A.    On the Effective Date as herein defined and immediately prior to the effectiveness of this Amendment, Bank of America,
N.A. is assigning a portion of its Commitment and its Loans to Royal Bank of Canada pursuant to a Lender Assignment Agreement. 

        B.    The Borrower has requested certain amendments to the Credit Agreement in order to, among other things, (i) decrease
the amount of the Commitments, (ii) shorten the maturity, (iii) add a borrowing base, (iv) amend certain financial covenants, and (v) revise the amortization schedule. 

        C.    Subject to the terms and conditions of this Amendment, the Administrative Agent and the undersigned Lenders are willing to
agree to such amendments. 

        Accordingly,
for adequate and sufficient consideration, the parties hereto agree, as follows: 

 Paragraph 1. Amendments.  

        1.1  Definitions.

        (a)  The
definition of "Accrued Columbia Settlement Balances" is inserted alphabetically into  Section 1.1: 

"Accrued Columbia Settlement Balances' means the amount of natural gas which has been earned by the Borrower to date pursuant to the Settlement
Agreement dated as of October 16, 1999, between the Borrower and Columbia Gas Transmission Corporation ("Columbia") (the
"Settlement Agreement"), provided that such amounts shall not be included if: 

	(i)
	the
Administrative Agent fails to have a first priority Lien on the Borrower's right, title and interest in and to the Settlement Agreement;

	(ii)
	Columbia
has disputed, or is in default of any of, its obligations under the Settlement Agreement;

	(iii)
	Columbia
is the subject of any of the events of the type described in clause (v) of the definition of Eligible Midstream Accounts
Receivable; or

	(iv)
	any
other event or condition occurs or exists which leads the Required Lenders to believe, in the exercise of their reasonable judgment, that the
Borrower's prospect of receiving, or the Lenders' ability to exercise their Lien on, the natural gas in question could reasonably be expected to be impaired." 

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        (b)  The
definition of "Applicable Margin" is amended in its entirety to read as follows: 

"Applicable Margin' means, with respect to any Loan of any type or any Letter of Credit, and at such time as the Leverage Ratio is in one of the
following ranges, the number of basis points ("b.p.") per annum for the relevant type of Loan, Commitment Fee or Letter of Credit and the relevant range
set forth below: 

	 
	 	 
	 	Applicable Margin

	Pricing

Level
	 	Leverage Ratio
	 	LIBO Rate

Loan
	 	Letter of

Credit
	 	Base Rate Loan
	 	Commitment Fee

	1	 	Less than or equal to 1.0X	 	175.0 b.p.	 	175.0 b.p.	 	37.5 b.p.	 	25.0 b.p.
	2	 	Greater than 1.0X, but less than or equal to 2.0X	 	200.0 b.p.	 	200.0 b.p.	 	62.5 b.p.	 	30.0 b.p.
	3	 	Greater than 2.0X, but less than or equal to 2.75X	 	225.0 b.p.	 	225.0 b.p.	 	87.5 b.p.	 	37.5 b.p.
	4	 	Greater than 2.75X, but less than or equal to 3.25X	 	250.0 b.p.	 	250.0 b.p.	 	112.5 b.p.	 	50.0 b.p.
	5	 	Greater than 3.25X	 	275.0 b.p.	 	275.0 b.p.	 	137.5 b.p.	 	50.0 b.p.

The
Leverage Ratio shall be determined from the then most recent quarterly financial statements delivered by the Borrower pursuant to  Section 7.1.1, and any changes in Applicable Margin shall become
effective the first day of the third month following the date such financial
statements are dated. In the event that the Borrower shall at any time fail to furnish the Lenders such financial statements required to be delivered under  Section 7.1.1, the maximum Applicable
Margin and Commitment Fee as set forth above shall apply until such time as such financial statements are
so delivered. Changes in the Applicable Margin and Commitment Fee as a result of a change in the Leverage Ratio will occur automatically as aforesaid without notice. The Applicable Margin and
Commitment Fee shall be set at Pricing Level 4 for the period beginning on the Effective Date and ending on June 30, 2002, unless during such
period the Leverage Ratio falls within Pricing Level 5, in which case Pricing Level 5 will apply." 

        (c)  The
following definition of "Available Borrowing Base" is inserted alphabetically into  Section 1.1: 

"Available Borrowing Base' means, at the particular time in question, the U.S. Borrowing Base in effect minus the U.S. Effective Amount at such time." 

        (d)  The
following definition of "Canadian Borrowing Base" is inserted alphabetically into  Section 1.1: 

"Canadian Borrowing Base' means the Canadian Dollar Equivalent of the amount of the Global Semi-Annual Borrowing Base allocated to the
Canadian Facility pursuant to Section 2.1.3(a)(ii), provided,  however, in no event shall the Canadian
Borrowing Base ever exceed the sum of the Revolving Loan Commitment Amount as defined in the Canadian Credit
Agreement and Term Loans outstanding under the Canadian Credit Agreement." 

        (e)  The
definition of "Canadian Dollar Equivalent" is hereby amended to read as follows: 

"Canadian Dollar Equivalent' means, with respect to an amount denominated in Dollars, the amount of the CAN$ which would be required to purchase such
amount of Dollars at the Noon Rate (as defined in the Canadian Credit Agreement) for such currencies on the applicable date (unless such date is not a Business Day, in which case the applicable date
shall be the Business Day immediately proceeding such date of determination). For the purpose of determining the "Canadian Dollar Equivalent' in connection with determination and allocation 

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of the Global Semi-Annual Borrowing Base and the Canadian Borrowing Base, the date of determination shall be the effective date of the applicable Reserve Report." 

        (f)    The
following definition of "Canadian Effective Amount" is inserted alphabetically into  Section 1.1: 

"Canadian Effective Amount' means, on any date, the aggregate outstanding principal amount of all Loans under the Canadian Facility after giving effect
to any prepayments or repayments of such Loans occurring on such date plus the Letter of Credit Outstandings under the Canadian Facility." 

        (g)  The
following definition of "Eligible Midstream Accounts Receivable" is inserted alphabetically into  Section 1.1: 

"Eligible Midstream Accounts Receivable' shall mean Midstream Accounts Receivable, excluding any Midstream Account Receivable: 

	(i)
	with
respect to which more than ninety (90) days have elapsed since the date of the original invoice;

	(ii)
	with
respect to which any of the representations, warranties, covenants, and agreements contained in any Collateral Document are incorrect or have been
breached in any material respect;

	(iii)
	with
respect to which, in whole or in part, a check, promissory note, draft, trade acceptance or other instrument for the payment of money has been
received, presented for payment and returned uncollected for any reason for such Midstream Account Receivable (or any other Midstream Account Receivable due from such account debtor);

	(iv)
	which
represents a progress billing (as hereinafter defined) or as to which the Borrower or any of its Subsidiaries has extended the time for payment
without the consent of the Administrative Agent; for the purposes hereof, "progress billing" means any invoice for goods sold or leased or services rendered under a contract or agreement pursuant to
which the account debtor's obligation to pay such invoice is conditioned upon the Borrower's or any of its Subsidiaries' completion of any further performance under the contract or agreement;

	(v)
	with
respect to which any one or more of the following events has occurred to the account debtor on such Midstream Account Receivable: death or judicial
declaration of incompetency of an account debtor who is an individual; the filing by or against the account debtor of a request or petition for liquidation, reorganization, arrangement, adjustment of
debts, adjudication as a bankrupt, winding-up, or other relief under the bankruptcy, insolvency, or similar laws of the United States, any state or territory thereof, or any foreign
jurisdiction, now or hereafter in effect; the making of any general assignment by the account debtor for the benefit of creditors; the appointment of a receiver or trustee for the account
debtor or for any of the assets of the account debtor, including, without limitation, the appointment of or taking possession by a "custodian," as defined in the U.S. Federal Bankruptcy Code; the
institution by or against the account debtor of any other type of insolvency proceeding (under the bankruptcy laws of the United States or otherwise) or of any formal or informal proceeding for the
dissolution or liquidation of, settlement of claims against, or winding up of affairs of, the account debtor; the sale, assignment, or transfer of all or any material part of the assets of the account
debtor; the nonpayment generally by the account debtor of its debts as they become due; or the cessation of the business of the account debtor as a going concern; 

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	(vi)
	if
fifteen percent (15%) or more of the aggregate Dollar amount of outstanding Midstream Accounts Receivable owed at such time by the account debtor
thereon is classified as ineligible under clause (i) above, provided, however, any Midstream
Account Receivable classified as ineligible under clause (i) above shall not be included in the calculation of the fifteen percent (15%) threshold in this  clause (vi) if such Midstream
Account Receivable is the subject of a bona fide dispute between such account debtor and the Borrower;

	(vii)
	owed
by an account debtor which: (1) does not maintain its chief executive office in the United States; or (2) is not organized under
the laws of the United States or any state thereof; or (3) is the government of any foreign country or sovereign state, or of any state, province, municipality, or other political subdivision
thereof, or of any department, agency, public corporation, or other instrumentality thereof; except to the extent that such Midstream Account Receivable is secured or payable by a letter of credit
satisfactory to the Administrative Agent in its discretion;

	(viii)
	owed
by an account debtor which is an Affiliate or employee of the Borrower or any of its Subsidiaries;

	(ix)
	except
as provided in clause (xi) below, with respect to which either the perfection,
enforceability, or validity of the Administrative Agent's Liens in such Midstream Account Receivable, or the Administrative Agent's right or ability to obtain direct payment to the Administrative
Agent of the proceeds of such Midstream Account Receivable, is governed by any federal, state, or local statutory requirements other than those of the U.C.C.;

	(x)
	owed
by an account debtor to which the Borrower or any of its Subsidiaries, is indebted in any way, or which is subject to any right of setoff or
recoupment by the account debtor, unless the account debtor has entered into an agreement acceptable to the Administrative Agent to waive setoff rights; or if the account debtor thereon has disputed
liability or made any claim with respect to any other Midstream Account Receivable due from such account debtor; but in each such case only to the extent of such indebtedness, setoff, recoupment,
dispute, or claim;

	(xi)
	owed
by the government of the United States, or any department, agency, public corporation, or other instrumentality thereof, unless the Federal
Assignment of Claims Act of 1940, as amended (31 U.S.C. § 3727 et seq.), and any other steps necessary to perfect the Administrative Agent's Liens therein, have been complied with to the
Administrative Agent's satisfaction with respect to such Midstream Account Receivable;

	(xii)
	owed
by any state, municipality, or other political subdivision of the United States, or any department, agency, public corporation, or other
instrumentality thereof and as to which the Administrative Agent determines that its Lien therein is not or cannot be perfected;

	(xiii)
	which
represents a sale on a bill-and-hold, guaranteed sale, sale and return, sale on approval, consignment, or
other repurchase or return basis;

	(xiv)
	which
is evidenced by a promissory note or other instrument or by chattel paper;

	(xv)
	if
the Required Lenders believe, in the exercise of their reasonable judgment, that the prospect of collection of such Midstream Account Receivable is
reasonably likely to be impaired or that the Midstream Account Receivable could reasonably be expected not to be paid by reason of the account debtor's financial inability to pay; 

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	(xvi)
	with
respect to which the account debtor is located in any state requiring the filing of a Notice of Business Activities Report or
similar report in order to permit the Borrower or any of its Subsidiaries to seek judicial enforcement in such state of payment of such Midstream Account Receivable, unless such Borrower or Subsidiary
has qualified to do business in such state or has filed a Notice of Business Activities Report or equivalent report for the then current year;

	(xvii)
	which
arises out of a sale not made in the ordinary course of the Borrower's or any of its Subsidiaries' Midstream Business;

	(xviii)
	with
respect to which the goods giving rise to such Midstream Account Receivable have not been shipped and delivered to and accepted
by the account debtor or the services giving rise to such Midstream Account Receivable have not been performed by the Borrower or its Subsidiary, as applicable, and, if applicable, accepted by the
account debtor, or the account debtor revokes its acceptance of such goods or services;

	(xix)
	owed
by an account debtor which is obligated to the Borrower or any of its Subsidiaries respecting Midstream Accounts Receivable the
aggregate unpaid balance of which exceeds twenty percent (20%) of the aggregate unpaid balance of all Midstream Accounts Receivable owed to the Borrower or any of its Subsidiaries at such time by all
of the Borrower's and its Subsidiaries account debtors, but only to the extent of such excess; provided, however, that account debtors Columbia Natural
Resources, Inc., a subsidiary of N:Source Inc. and Equitable Production Company, a subsidiary of Equitable Resources, Inc., shall not be subject to the foregoing twenty percent
(20%) limitation;

	(xx)
	which
is not subject to a first priority and perfected security interest in favor of the Administrative Agent for the benefit of the Lenders; or

	(xxi)
	which
the Administrative Agent and the Required Lenders in their reasonable discretion determine to be ineligible. 

If
any Midstream Account Receivable at any time ceases to be an Eligible Midstream Account Receivable, then such Midstream Account Receivable shall promptly be excluded from the calculation of
Eligible Midstream Accounts Receivable." 

        (h)  The
following definition of "Eligible Midstream Inventory" is inserted alphabetically into  Section 1.1: 

"Eligible Midstream Inventory' shall mean (i) Accrued Columbia Settlement Balances and (ii) all Midstream Inventory excluding any
Midstream Inventory: 

	(i)
	that
is not owned by the Borrower or any of its Domestic Subsidiaries;

	(ii)
	that
is not subject to the Administrative Agent's Liens, which are perfected as to such Midstream Inventory, or that are subject to any other Lien
whatsoever (other than the Liens described in clause (f) and (o) (to the extent
clause (ix) below has been complied with) of Section 7.2.3 provided that such Permitted Liens (1) are junior in priority to
the Administrative Agent's Liens and (2) do not impair directly or indirectly the ability of the Administrative Agent to realize on or obtain the full benefit of such Midstream Inventory);

	(iii)
	that
does not consist of finished goods or raw materials;

	(iv)
	that
consists of work-in-process, samples, prototypes, supplies, or packing and shipping materials; 

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	(v)
	that
is not in good condition, is unmerchantable, or does not meet all standards imposed by any governmental authority, having regulatory authority over
such goods, their use or sale;

	(vi)
	that
is obsolete or returned or repossessed or used goods taken in trade;

	(vii)
	that
is located outside the United States of America (or that is in-transit from vendors or suppliers);

	(viii)
	that
is located in a public warehouse or in possession of a bailee or in a facility leased by the Borrower of any of its Subsidiaries,
if the warehouseman, or the bailee, or the lessor has not delivered to the Administrative Agent, if requested by the Administrative Agent, a subordination agreement in form and substance satisfactory
to the Administrative Agent or if a sufficient amount has been deducted from the value of such Midstream Inventory to cover rents or storage charges;

	(ix)
	that
contains or bears any intellectual property rights licensed to the Borrower or any of its Subsidiaries by any Person, if the Administrative Agent
is not satisfied that it may sell or otherwise dispose of such Midstream Inventory in accordance with the terms of any Collateral Document and Section 8.3  without infringing the rights of the
licensor of such intellectual property rights or violating any contract with such licensor (and without payment of any royalties other than
any royalties due with respect to the sale or disposition of such Midstream Inventory pursuant to the existing license agreement), and, as to which the Borrower has not delivered to the Administrative
Agent a consent or sublicense agreement from such licensor in form and substance acceptable to the Administrative Agent if requested;

	(x)
	that
is not reflected in the details of a current perpetual inventory report;

	(xi)
	that
is Midstream Inventory placed on consignment; or

	(xii)
	which
the Administrative Agent and the Required Lenders in their reasonable discretion determine to be ineligible. 

If
any Midstream Inventory at any time ceases to be Eligible Midstream Inventory, such Midstream Inventory shall promptly be excluded from the calculation of Eligible Midstream Inventory." 

        (i)    The
definition of "Fixed Charge Coverage Ratio" is amended by (i) deleting the term "12 months" and
replacing it with the term "four Fiscal Quarters" and (ii) deleting each reference to the term "12-month" and replacing each such reference with the term "four-Fiscal
Quarter." 

        (j)    The
following definition of "Global Borrowing Base" is inserted alphabetically in  Section 1.1: 

"Global Borrowing Base' means at the particular time in question, the sum of (i) the Global Semi-Annual Borrowing Base and
(ii) the U.S. Monthly Borrowing Base, provided, however, in no event shall the Global Borrowing
Base ever exceed the sum of (i) the Revolving Loan Commitment Amount plus the Term Loans outstanding hereunder and (ii) the U.S. Dollar Equivalent of the Revolving Loan Commitment Amount
plus Term Loans as defined in and outstanding under the Canadian Credit Agreement." 

        (k)  The
following definition of "Global Lenders" is inserted alphabetically in  Section 1.1: 

"Global Lenders' means the Lenders hereunder and the Lenders under the Canadian Credit Agreement." 

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        (l)    The
following definition of "Global Semi-Annual Borrowing Base" is inserted alphabetically into  Section 1.1: 

"Global Semi-Annual Borrowing Base' means at the particular time in question, the amount provided for in  Section 2.1.3(a), provided, however, in no event
shall the Global Semi-Annual Borrowing Base ever exceed the sum of (i) the Revolving Loan Commitment Amount plus the Term Loans outstanding and (ii) the U.S. Dollar
Equivalent of the Revolving Loan Commitment Amount plus Term Loans as defined in and outstanding under the Canadian Credit Agreement." 

        (m)  The
following definition of "Hedged Eligible Midstream Inventory" is inserted alphabetically into  Section 1.1: 

"Hedged Eligible Midstream Inventory' means Eligible Midstream Inventory subject to a Hedging Agreement with respect to such inventory and satisfactory
to the Administrative Agent and the Required Lenders." 

        (n)  The
definition of "Leverage Ratio" is amended by (i) deleting the phrase "twelve months most recently
ended" and replacing it with the phrase "four Fiscal Quarters most recently ended" and (ii) deleting each reference to the term "12 months" and replacing each such reference with the
term "four Fiscal Quarters." 

        (o)  The
following definition of "Midstream Accounts Receivable" is inserted alphabetically into  Section 1.1: 

"Midstream Accounts Receivable' means and includes all of the Borrower's and its Domestic Subsidiaries' now owned or hereafter acquired or arising
accounts, as defined in the U.C.C., including any rights to payment for the sale or lease of goods or rendition of services, whether or not they have been earned by performance, which arise as a
result of the Midstream Business." 

        (p)  The
following definition of "Midstream Business" is inserted alphabetically into  Section 1.1: 

"Midstream Business' means any and all operations of the Borrower and its Domestic Subsidiaries in the United States related to the gathering and
processing of natural gas and the fractionation, transportation, marketing, and storage of natural gas liquids." 

        (q)  The
following definition of "Midstream Inventory" is inserted alphabetically into  Section 1.1: 

"Midstream Inventory' shall mean, for any of the Borrower and its Domestic Subsidiaries, all now owned or hereafter acquired inventory, goods and
merchandise, wherever located, to be furnished under any contract of service or held for sale or lease, all returned goods, raw materials, work-in-process, finished goods
(including embedded software), other materials and supplies of any kind, nature or description which are used or consumed in the Midstream Business or used in connection with the packing, shipping,
advertising, selling or finishing of such goods, merchandise, each valued at the lower of cost or market, and all documents of title or other documents (as defined in the U.C.C.) representing them." 

        (r)  The
following definition of "Midstream Report" is inserted alphabetically into  Section 1.1: 

"Midstream Report' means a report, covering the Midstream Business, and any related non-Oil and Gas Properties businesses, prepared in
accordance with customary and prudent practices in form and substance acceptable to the Administrative Agent, setting forth (a) the total quantity of gas and liquids to be gathered, processed
and fractionated, (b) the estimated future net revenues and cumulative estimated future net revenues, (c) the present discounted value of future net revenues, and (d) such other
information and data with respect to the 

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Midstream Business, and any related non-Oil and Gas Properties businesses, as the Administrative Agent may reasonably request." 

        (s)  The
following definition of "Required Global Lenders" is inserted alphabetically in  Section 1.1: 

"Required Global Lenders' means, at any time, the Administrative Agent and Global Lenders holding at least 66% of the then aggregate outstanding
principal amount of the Notes and the Notes under the Canadian Credit Agreement then held by the Global Lenders, or, if no such principal amount is then outstanding, the Administrative Agent and the
Global Lenders having at least 66% of the aggregate Commitments and the U.S. Dollar Equivalent of the Commitments under the Canadian Credit Agreement." 

        (t)    The
definition of "Revolving Loan Commitment Amount" is amended by deleting the number "$55,000,000" and replacing it
with the number "$45,000,000." 

        (u)  The
definition of "Revolving Loan Commitment Termination Date" is amended by deleting the number "2005" and replacing it
with the number "2004." 

        (v)  The
following definition of "Semi-Annual Borrowing Base Period" is inserted alphabetically into  Section 1.1: 

"Semi-Annual Borrowing Base Period' means with respect to the Semi-Annual Borrowing Base the period from March 29, 2002,
to April 30, 2002, and each six-month period commencing May 1, 2002, and each subsequent November 1 and May 1 thereafter." 

        (w)  The
definition of "Stated Maturity Date" is amended by deleting the number "2005" and replacing it with the number
"2004." 

        (x)  The
following definition of "U.S. Borrowing Base" is inserted alphabetically in  Section 1.1: 

"U.S. Borrowing Base' means the sum of (i) the U.S. Semi-Annual Borrowing Base and (ii) the U.S. Monthly Borrowing Base,  provided, however, in no event shall the U.S. Borrowing Base ever exceed the sum of the Revolving Loan
Commitment Amount and the Term Loans outstanding." 

        (y)  The
definition of "U.S. Dollar Equivalent" is hereby amended to read as follows: 

"U.S. Dollar Equivalent' with respect to an amount denominated in CAN$, (a) means, for purposes of the definition of the term "Canadian
Commitment Portion,' the amount of Dollars required to purchase the relevant stated amount of CAN$based on the Noon Rate (as defined in the Canadian Credit Agreement) in effect on such day and
(b) means, for purposes of the definitions of "Global Borrowing Base' and "Required Global Lenders' and for purposes of Section 2.1.3(a),
the amount of Dollars required to purchase the relevant stated amount of CAN$based on the Noon Rate (as defined in the Canadian Credit Agreement) in effect on the effective date of the applicable
Reserve Report." 

        (z)  The
following definition of "U.S. Effective Amount" is inserted alphabetically into  Section 1.1: 

"U.S. Effective Amount' means, on any date, the aggregate outstanding principal amount of all Loans after giving effect to any prepayments or repayments
of Loans occurring on such date plusthe Letter of Credit Outstandings." 

        (aa) The
following definition of "U.S. Monthly Borrowing Base" is inserted alphabetically into  Section 1.1: 

"U.S. Monthly Borrowing Base' has the meaning set forth in Section 2.1.3(b)." 

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        (bb) The
following definition of "U.S. Monthly Borrowing Base Certificate" is inserted alphabetically into  Section 1.1: 

"U.S. Monthly Borrowing Base Certificate' means a certificate in the form of Exhibit N or any
other form approved by the Administrative Agent, together with all attachments contemplated thereby." 

        (cc) The
following definition of "U.S. Semi-Annual Borrowing Base" is inserted alphabetically into  Section 1.1: 

"U.S. Semi-Annual Borrowing Base' means the amount of the Global Semi-Annual Borrowing Base allocated to the Revolving Facility
and the Term Loan Facility pursuant to Section 2.1.3(a)(ii), provided,  however, in no event shall the
U.S. Borrowing Base ever exceed the sum of the Revolving Loan Commitment Amount and the Term Loans outstanding." 

        (dd) The
following definition of "Unhedged Eligible Midstream Inventory" is inserted alphabetically into  Section 1.1: 

"Unhedged Eligible Midstream Inventory' means all Eligible Midstream Inventory other than Hedged Eligible Midstream Inventory." 

        1.2  Section 2.1.1(b). Section 2.1.1(b) is deleted in its
entirety and amended to read as follows: 

        "(b) On
the terms and subject to the conditions hereof, each Lender severally, but not jointly, agrees to lend to the Borrower such Lender's Percentage of one or more Borrowings
under the Revolving Facility, not to exceed such Lender's Percentage of the lesser of (i) the Revolving Loan Commitment Amount and (ii) the U.S. Borrowing Base less the aggregate amount
of all Term Loans outstanding." 

        1.3  Section 2.1.3.  Section 2.1.3 is deleted in its entirety and amended to read as
follows: 

        "SECTION
2.1.3 Global Borrowing Base Determinations.

        (a) (i) Global Semi-Annual Borrowing Base Determinations. From and after March 29, 2002, the U.S.
Semi-Annual Borrowing Base shall be $65,000,000 and the Global Semi-Annual Borrowing Base shall be $100,000,000, each until redetermined hereunder. The Global
Semi-Annual Borrowing Base shall be redetermined for each Semi-Annual Borrowing Base Period by the Global Lenders. The Global Semi-Annual Borrowing Base shall be
determined based upon the Oil and Gas Properties reflected in the most recently delivered Reserve Report and the assets reflected in the most recently delivered Midstream Report, and such credit and
other factors (including without limitation the assets, liabilities, cash flow, business, properties, prospects, management and ownership of the Borrower, MarkWest Canada Co., and their respective
Subsidiaries (excluding Midstream Accounts Receivable and Midstream Inventory) as the Global Lenders deem relevant. The Global Lenders' determination of the Global Semi-Annual Borrowing
Base shall be in each of their sole discretion, exercised in accordance
with its standard and usual practice for determining borrowing base loans that it generally applies to borrowers in the oil and gas business. On or before April 15 and October 15 of each
year, the Administrative Agent shall recommend to the Global Lenders a new Global Semi-Annual Borrowing Base, a copy of which recommendation shall be provided concurrently to the Borrower.
The Global Lenders shall, within fifteen (15) days of such recommendation (by unanimous agreement in the case of increasing the Global Semi-Annual Borrowing Base and by agreement of
the Required Global Lenders in the case of maintaining or decreasing the Global Semi-Annual Borrowing Base), inform the Administrative Agent in writing as to whether such Global Lender
agrees or disagrees with the Administrative Agent's recommendation. If a Global Lender disagrees, such notice shall contain the highest amount such Global Lender has approved for the Global
Semi-Annual Borrowing Base. If at the end 

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of such fifteen (15) day period any Global Lender has not communicated its approval or disapproval, such silence shall be deemed to be its approval. If the Administrative Agent's recommended
Global Semi-Annual Borrowing Base is not approved or deemed approved as aforesaid by the Required Global Lenders at the end of such fifteen (15) day period, the Global
Semi-Annual Borrowing Base shall be the highest amount on which all of the Global Lenders can agree if increasing the Global Semi-Annual Borrowing Base or all of the Required
Global Lenders can agree if maintaining or decreasing the Global Semi-Annual Borrowing Base. After such re-determined Global Semi-Annual Borrowing Base is approved
or otherwise determined as aforesaid, the Administrative Agent will notify the Borrower and the Global Lenders of the amount of the re-determined Global Semi-Annual Borrowing
Base, and such amount shall become effective as of the next succeeding May 1 or November 1, as applicable. If the Borrower does not furnish the Reserve Reports or all such other
information and data by the date required, the Global Lenders may nonetheless determine a new Global Semi-Annual Borrowing Base. It is expressly understood that the Global Lenders shall
have no obligation to determine the Global Semi-Annual Borrowing Base at any particular amount, either in relation to the Commitment Amount or otherwise. 

        (ii)
Global Semi-Annual Borrowing Base Allocations. The Global Semi-Annual Borrowing Base shall be comprised of
the U.S. Semi-Annual Borrowing Base and the Canadian Borrowing Base, and the sum of the U.S. Semi-Annual Borrowing Base and the Canadian Borrowing Base shall not exceed the
Global Semi-Annual Borrowing Base. From and after March 29, 2002, the U.S. Semi-Annual Borrowing Base shall be $65,000,000 and the Canadian Borrowing Base shall be the
Canadian Dollar Equivalent of $35,000,000, until redetermined hereunder. Within three (3) Business Days of each redetermination of the Global Semi-Annual Borrowing Base pursuant to  Section 2.1.3(a)(i), the Administrative Agent shall notify the Borrower in writing of such redetermination. Upon receipt by the Borrower of such
notice of redetermination, the Borrower shall, within ten (10) days, allocate the Global Semi-Annual Borrowing Base between the U.S. Semi-Annual Borrowing Base and the
Canadian Borrowing Base (utilizing the Canadian Dollar Equivalent) and notify the Administrative Agent in writing of such allocation. Subject to the last sentence of this  Section 2.1.3(a)(ii), the
Borrower shall, in its sole discretion, allocate the U.S. Borrowing Base to the Revolving Facility and the Term Loan
Facility; provided however, that in the event a Default or Event of Default shall exist, such allocation shall be done by the Administrative Agent
acting with the concurrence of the Required Lenders. In the event the Borrower fails to provide the Administrative Agent such notice of allocation, the Global Semi-Annual Borrowing Base
shall be allocated by the Administrative Agent in the same proportion as existed prior to such redetermination. Promptly upon such allocation of the Global Semi-Annual Borrowing Base, the
Administrative Agent shall notify the Global Lenders, the Borrower, and the Canadian Administrative Agent in writing of the amount of the U.S. Semi-Annual Borrowing Base and the Canadian
Borrowing Base to be in effect during the relevant Semi-Annual Borrowing Base Period. Notwithstanding the foregoing, the Borrower
may not allocate a U.S. Dollar Equivalent amount to the Canadian Borrowing Base which is less than the U.S. Dollar Equivalent of the Canadian Effective Amount at the time of such allocation. 

        (iii)
Special Global Semi-Annual Borrowing Base Determinations. In addition to the Global Semi-Annual Borrowing
Base determinations made pursuant to Section 2.1.3(a)(i), the Borrower and the Administrative Agent (acting upon the direction of the Required
Global Lenders) may each request one (1) additional Global Semi-Annual Borrowing Base redetermination during each Semi-Annual Borrowing Base Period (each such additional
determination herein called a "Special Global Semi-Annual Borrowing Base Determination"). In the event the Borrower requests a Special
Global Semi-Annual Borrowing Base Determination 

10

 

pursuant to this Section 2.1.3(a)(iii), the Borrower shall deliver written notice of such request to the Global Lenders which shall include a
Reserve Report prepared by the Borrower as of a date not more than thirty (30) calendar days prior to the date of such request, for the benefit of the Global Lenders. Following receipt
by the Administrative Agent of such request, the Administrative Agent may request in writing other information and the Borrower shall provide such information prepared as of a date not more than
thirty (30) calendar days prior to the date of such request. Each Special Global Semi-Annual Borrowing Base Determination shall be made pursuant to the procedures set forth
in Section 2.1.3(a)(i), and the Administrative Agent shall give the Borrower notice of the redetermined Global Semi-Annual Borrowing
Base pursuant to Section 2.1.3(a)(i), and the Borrower shall allocate the Global Semi-Annual Borrowing Base between the Canadian
Borrowing Base and the U.S. Semi-Annual Borrowing Base pursuant to Section 2.1.3(a)(ii). 

        (b) U.S. Monthly Borrowing Base Determinations. The U.S. Monthly Borrowing Base (the "U.S. Monthly
Borrowing Base") shall be equal to the lesser of (i) the sum of seventy-five percent (75%) of the Eligible Midstream Accounts Receivable,
seventy-five percent (75%) of the Unhedged Eligible Midstream Inventory, and (85%) of the Hedged Eligible Midstream Inventory; and (ii) $20,000,000. The U.S. Monthly Borrowing Base
shall be determined each month by reference to the most recent U.S. Monthly Borrowing Base Certificate delivered to the Administrative Agent (absent any error in such U.S. Monthly Borrowing Base
Certificate) which shall be effective as of the date such certificate is required to be delivered pursuant to Section 7.1.1(m)." 

        1.4.  Section 2.1.5.  Section 2.1.5 is amended by deleting each reference to the term
"Revolving Loan Commitment Amount" and replacing each such reference with the
term "U.S. Borrowing Base less the aggregate amount of all Term Loans outstanding." 

        1.5  Section 2.1.6. Section 2.1.6 is
amended by (i) deleting the number "$75,000,000" and replacing it with the number "$65,000,000" and (ii) deleting the number "$110,000,000" and replacing it with the number
"100,000,000." 

        1.6  Section 2.2.2.  Section 2.2.2 is amended by deleting the number "$3,667,000" and
replacing it with the number "$3,000,000." 

        1.7  Section 3.1(b).  Section 3.1(b) is deleted in its entirety and amended to read as
follows: 

        "(b) The Term Loans. The Borrower shall repay the principal of and interest on the Term Loans as follows: the Borrower shall make
principal payments on each date set forth below (each, a "Principal Payment Date"), such that the maximum outstanding Term Loans shall be reduced to the
dollar amount set forth below opposite such date. Each principal payment 

11

 

made on a Principal Payment Date shall be made together with accrued and unpaid interest thereon." 

	Principal Payment Date
 
	 	Term Loan Commitment

	March 31, 2002	 	$37,200,000
	June 30, 2002	 	$34,400,000
	September 30, 2002	 	$30,287,500
	December 31, 2002	 	$25,725,000
	March 31, 2003	 	$21,162,500
	June 30, 2003	 	$16,600,000
	September 30, 2003	 	$12,037,500
	December 31, 2003	 	$10,532,800
	March 31, 2004	 	$  9,028,100
	June 30, 2004	 	$  7,523,400
	August 9, 2004	 	The remaining principal balance of the Term Loan

        1.8  Section 3.1.2. Section 3.1.2 is deleted in its entirety and
amended to read as follows: 

        "SECTION
3.1.2 Mandatory Prepayment.

        (a)  Mandatory Prepayments by Reason of Change in Borrowing Base. On any date (i) the U.S. Effective Amount shall
exceed the U.S. Borrowing Base or (ii) the sum of the U.S. Effective Amount and the U.S. Dollar Equivalent of the Canadian Effective Amount shall exceed the Global Borrowing Base, then the
Borrower shall make mandatory prepayments of Revolving Loans equal to such excess, and if any such excess remains after such prepayments, the Borrower shall make mandatory prepayments of Term Loans
equal to the remaining amount of such excess, and if any such excess remains after such prepayments, to the extent of such excess the Borrower shall immediately Cash Collateralize the Reimbursement
Obligations in an amount equal to the aggregate Stated Amount of all Letters of Credit outstanding and undrawn. Notwithstanding the foregoing, the Borrower may, with the consent of the Required
Lenders, in lieu of making mandatory prepayments of all or a portion of the Term Loans, prepay all or a portion of outstanding Loans under the Canadian Facility. The Borrower shall (A) make
fifty percent (50%) of such prepayments within ninety (90) days following its receipt of the written notice of the Global Borrowing Base redetermination in accordance with  Section 2.1.3(a)(i) or Section 2.1.3.(a)(iii) and the remaining fifty
percent (50%) of such prepayments within one hundred eighty (180) days following its receipt of the notice of the Global Borrowing Base redetermination, (B) make such prepayment within
thirty (30) days following its delivery of the U.S. Monthly Borrowing Base Certificate pursuant to Section 7.1.1(m), or (C) make
such prepayment on the date of any Sale which results in a reduction in the U.S. Semi-Annual Borrowing Base pursuant to  Section 7.2.9(b). Subject to the last sentence of Section 2.1.3(a)(i), Revolving Loans
prepaid pursuant to this Section 3.1.2(a) may be reborrowed to the extent the Global Borrowing Base subsequently is redetermined to a
level that would allow such reborrowing and the other conditions to Borrowing have been satisfied. 

        (b)  Mandatory Prepayments: Annual Clean Down. At least once each calendar year, the Borrower shall make mandatory prepayments
as provided in this Subsection (b) so that the U.S. Effective Amount equals the U.S. Semi-Annual Borrowing Base. Such prepayments
shall be applied first, to repay Revolving Loans, then to repay Term Loans, and then to Cash Collateralize Letters of Credit." 

12

 

        1.9  Section 3.3.2.  Section 3.3.2 is amended to add the following phrase immediately
prior to the period at the end of such section: 

        "and
to Administrative Agent, as an annual engineering fee, $5,000 on each April 30, commencing April 30, 2002, until the Stated Maturity Date." 

        1.10 Section 7.1.1(c).  Section 7.1.1(c) is amended by deleting the term "month" and
replacing it with the term "Fiscal Quarter." 

        1.11 Section 7.1.1(k).  Section 7.1.1(k) is amended to read as follows: 

        "(k)(i) on
or before April 1 of each year, a Reserve Report, effective January 1 of such year, prepared by an independent petroleum engineer acceptable to the
Required Global Lenders (the "Independent Engineer"), and annually commencing October 1, 2002, effective as of July 1 of each year, a
Reserve Report prepared by personnel of the Borrower, (ii) together with each Reserve Report, a certificate from an officer of the Borrower with principal responsibility for reserve engineering
certifying that, to the best of his knowledge: (A) the information contained in the Reserve Report has been prepared in accordance with customary and prudent practices in the petroleum
engineering industry and Financial Accounting Standards Board Statement 69, (B) attached to the certificate is a schedule of the Oil and Gas Properties evaluated by such Reserve Report that are
subject to the Lien of the Collateral Documents; and (C) attached to the certificate is a list of all marketing agreements not cancelable on 60 days or less notice (without penalty or
detriment) for the sale of production at a fixed price from the Borrower's or its Subsidiaries' Oil and Gas Properties (including, without limitation, calls on, or other rights to purchase, production
whether or not the same are currently being exercised), and (iii) on or before April 1 and October 1 of each year, effective as of January 1 and July 1,
respectively, a Midstream Report prepared by personnel of the Borrower and accompanied by a certificate of a technical officer of the Borrower certifying that, to the best of his knowledge, the
information contained in the Midstream Report has been prepared in accordance with customary and prudent practices in the petroleum engineering industry." 

        1.12 Section 7.1.1(m).  Section 7.1.1 is amended by re-designating clause (m) to be
clause (n) and adding the following  Section 7.1.1(m): 

        "(m)
within ten (10) Business Days after the end of each calendar month, (i) a completed Borrowing Base Certificate calculating and certifying the U.S. Monthly Borrowing
Base as of the last day of such calendar month, certified as complete and correct and signed on behalf of the Borrower by its chief financial officer, and (ii) such other supporting
documentation and additional reports with respect to the U.S. Monthly Borrowing Base as the Administrative Agent shall request; and" 

        1.13 Section 7.1.8. Section 7.1.8 is amended to add the
following phrase immediately prior to the period at the end of subsections (a) and (b): 

",
provided, MarkWest Energy Partners, L.P., a Delaware limited partnership, and each of its Subsidiaries and MarkWest Energy GP, L.L.C., a Delaware
limited liability company, shall not be required to comply with this Section so long as the only assets of such entities are cash or Cash Equivalent Investments in an aggregate amount not to
exceed $5,000.00." 

        1.14 Section 7.2.4(a).  Section 7.2.4(a) is amended by deleting each reference to the term
"month" and replacing each such reference with the term "Fiscal Quarter" and
deleting the term "after Closing" and replacing it with the term "after July 1, 2001." 

        1.15 Section 7.2.4(b).  Section 7.2.4(b) is amended by deleting the term "calendar month" and
replacing it with the term "Fiscal Quarter." 

13

 

para 

        1.16 Section 7.2.4(c).  Section 7.2.4(c) is deleted in its entirety and amended to read as
follows: 

        "(c) Its
Leverage Ratio to be greater than the amounts set forth below as of the last day of each Fiscal Quarter ending during the following periods: 

	Maximum Leverage Ratio
 
	 	As of the Date of

each Fiscal Quarter Ending

as Set Forth Below

	4.00	 	12/31/01
	3.75	 	3/31/02
	3.50	 	6/30/02
	3.25	 	9/30/02
	3.00	 	12/31/02 and Fiscal Quarters ending thereafter"

        1.17 Section 7.2.4(d).  Section 7.2.4(d)is deleted in its entirety and amended to read as
follows: 

        "(d) Its
Fixed Charge Coverage Ratio to be less than the amounts set forth below as of the last day of each Fiscal Quarter ending during the following periods: 

	Minimum Fixed Charge Coverage Ratio
 
	 	As of the Date of

each Fiscal Quarter Ending

as Set Forth Below

	1.40	 	12/31/01
	1.50	 	03/31/02 through 12/31/02
	1.75	 	3/31/03 and thereafter"

        1.18 Section 7.2.9(b). Section 7.2.9(b) is deleted in its
entirety and amended to read as follows: 

        "(b) The
Borrower will not, and will not permit any of its Subsidiaries to, sell, convey, contribute or transfer any asset (including, without limitation, any sale or assignment
with or without recourse of any receivable) except: (i) retirement of assets in the ordinary course of business; (ii) the sale of Oil and Gas production and sale of inventory in the
ordinary course of business, including in connection with hedge agreements or pursuant to long-term contracts; (iii) any conveyance or transfer by a Subsidiary of the Borrower to
the Borrower, or by a Subsidiary of the Borrower to a wholly owned Subsidiary of Borrower; (iv) transfers by the Borrower to a Subsidiary permitted by  Section 7.2.5; (v) transfers of
Hydrocarbon Interests which transfers constitute payments in kind pursuant to the Incentive Payments
Agreement; and (vi) any other sale, conveyance, contribution or transfer of any asset or assets other than accounts receivable (the transfers permitted pursuant to this
clause (vi) being referred to as a "Sale"), provided, any such Sales made since the date
of the most recent U.S. Semi-Annual Borrowing Base redetermination exceeding, individually or in the aggregate, ten percent (10%) of the U.S. Semi-Annual Borrowing Base then in
effect, shall result in a review of the U.S. Semi-Annual Borrowing Base as provided in this Section. The Borrower shall give the Administrative Agent and the Global Lenders notice of any
such proposed Sale not less than twenty (20) Business Days prior to the anticipated closing date of the proposed Sale. The Administrative Agent shall, within ten (10) Business Days and
utilizing the Reserve Report and Midstream Report delivered in connection with the most recent redetermination of the U.S. Semi-Annual Borrowing Base, and any other information deemed
relevant by the Administrative Agent, propose to the Global Lenders the amount of the U.S. Semi-Annual Borrowing Base to be in effect after such Sale. Thereafter, the Global Lenders shall
have eight (8) Business Days to approve or object to such proposed amount; and any failure to object shall be deemed to be an approval. In the event there is no approval or deemed 

14

 

approval, the Administrative Agent shall poll the Global Lenders to ascertain the greatest amount of the U.S. Semi-Annual Borrowing Base then acceptable to the Required Global Lenders and
such amount shall be the amount of the U.S. Semi-Annual Borrowing Base. The Administrative Agent shall give the Borrower and the Global Lenders notice of the amount of the revised U.S.
Semi-Annual Borrowing Base, and the Borrower may reallocate the sum of the revised U.S. Semi-Annual Borrowing Base and the Canadian Borrowing Base as provided in  Section 2.1.3(a)(ii).
Notwithstanding the foregoing, the Borrower shall not, nor shall the Borrower permit any of its Subsidiaries to, transfer
any assets, other than the sale of Oil and Gas production and inventory and payment of trade payables in the ordinary course of business pursuant to  Section 7.2.9(b)(ii), to any Person pursuant to
this Section 7.2.9 if a Default shall have
occurred and be continuing or would otherwise be existing after, or result from, any such transfer." 

        1.19 Section 7.2.15. A new  Section 7.2.15 is added to read as follows: 

"SECTION
7.2.15 Gas Imbalances, Take-or-Pay or Other Prepayments. The Borrower will not allow net gas imbalances in excess of
200,000 MMBTU of gas, take-or-pay or other prepayments with respect to the Oil and Gas Properties of the Borrower or its Subsidiaries that would require the Borrower or its
Subsidiaries to deliver Oil and Gas produced on Oil and Gas Properties at some future time without then or thereafter receiving full payment therefore." 

        1.20 Section 10.1(a).  Section 10.1(a) is amended by deleting the word
"or" appearing immediately before subclause (e) thereof and inserting the following phrase
immediately after such subclause (e): "or (f) increase the Global Borrowing Base pursuant to Section 2.1.3 without consent of the Global
Lenders, provided, the Required Global Lenders may maintain or decrease the Global Borrowing Base pursuant to  Section 2.1.3." 

        1.21 Schedule V.  Schedule V to the Credit Agreement is amended to read as set forth in
Schedule Vattached
hereto. 

        1.22 Exhibit F.  Exhibit F to the Credit Agreement is hereby amended to read as
Schedule V attached hereto. 

        1.23 Exhibit N.  Exhibit N attached hereto hereby is added to the Credit Agreement.

        Paragraph 2. Effective Date.    Notwithstanding any contrary provision, this Amendment is not
effective until the date (the "Effective Date") the following conditions are satisfied: 

        (a)  The
Administrative Agent shall have received counterparts of this Amendment, executed by the Borrower, the Guarantors, and the Required Lenders. 

        (b)  The
Borrower shall have executed and delivered a new Note reflecting the Commitments as amended except that new Notes shall not be required for the Lenders whose
Commitments have not changed. 

        (c)  The
Administrative Agent shall have received counterparts of the Guaranty (MarkWest Energy Appalachia, L.L.C.), the Pledge and Security Agreement (MarkWest Energy
Appalachia, L.L.C.), and the Acknowledgment of Pledge, each executed by MarkWest Energy Appalachia, L.L.C. and the related financing statement. 

        (d)  The
Administrative Agent shall have received from the Borrower and each Guarantor a certificate dated as of the Effective Date of its secretary, assistant secretary,
manager or general partner as applicable (i) as to resolutions of its board of directors or managers or their equivalent authorizing the execution and performance of this Amendment, and
(ii) if the officer executing this 

15

 

Amendment is not named in the incumbency certificate delivered at the time of execution of the Credit Agreement, as to the incumbency and signature of said officer. 

        (e)  The
Administrative Agent shall have received a legal opinion from counsel to the Borrower and each Guarantor as to the due authorization, execution and delivery of this
Amendment. 

        (f)    The
"Effective Date" shall occur simultaneously as defined in the First Amendment to the Canadian Credit Agreement. 

        (g)  Fees
and expenses required to be paid pursuant to Paragraph 5 of this Amendment have been paid to the extent invoiced prior to the Effective Date. 

        (h)  The
Administrative Agent shall have received such other assurances, certificates, documents and consents as the Administrative Agent may require. 

        Paragraph 3. Acknowledgment and Ratification.    As a material inducement to the Administrative
Agent and the Lenders to execute and deliver this Amendment, each of the Borrower and the Guarantors (a) consents to the agreements in this Amendment and (b) agrees and acknowledges that
the execution, delivery, and performance of this Amendment shall in no way release, diminish, impair, reduce, or
otherwise affect the respective obligations of the Borrower or any Guarantor under the Loan Documents to which it is a party, which Loan Documents shall remain in full force and effect, and all rights
thereunder are hereby ratified and confirmed. 

        Paragraph 4. Representations.    As a material inducement to the Administrative Agent and the
Lenders to execute and deliver this Amendment, each of the Borrower and the Guarantors represents and warrants to the Administrative Agent and the Lenders that as of the Effective Date of this
Amendment and as of the date of execution of this Amendment, (a) all representations and warranties in the Loan Documents are true and correct in all material respects as though made on the
date hereof, except to the extent that any of them speak to a different specific date, and (b) no Default or Event of Default exists. 

        Paragraph 5. Expenses.    The Borrower shall pay within ten (10) days of demand all
reasonable costs, fees, and expenses paid or incurred by the Administrative Agent incident to this Amendment, including, without limitation, the fees and expenses of the Administrative Agent's counsel
in connection with the negotiation, preparation, delivery, and execution of this Amendment and any related documents, filing and recording costs, and the costs of title insurance endorsements if
required. 

        Paragraph 6. Miscellaneous.    This Amendment is a "Loan Document"  referred to
in the Credit Agreement. The provisions relating to Loan Documents in Article 10 of the Credit Agreement are
incorporated in this Amendment by reference. Unless stated otherwise (a) the singular number includes the plural and vice versa and words of any
gender include each other gender, in each case, as appropriate, (b) headings and captions may not be construed in interpreting provisions, (c) this Amendment must be construed, and its
performance enforced, under Texas law and applicable U.S. federal law, (d) if any part of this Amendment is for any reason found to be unenforceable, all other portions of it nevertheless
remain enforceable, and (e) this Amendment may be executed in any number of counterparts with the same effect as if all signatories had signed the same document, and all of those counterparts
must be construed together to constitute the same document. 

        Paragraph 7. Entire Agreement.    This Amendment represents the final
agreement between the parties about the subject matter of this Amendment and may not be contradicted by evidence of prior, contemporaneous, or subsequent oral agreements of the parties. There are no
unwritten oral agreements between the parties.

        Paragraph 8. Parties.    This Amendment binds and inures to the benefit of the Borrower, the
Guarantors, the Administrative Agent, the Lenders, and their respective successors and assigns. 

16

 

        Paragraph 9. Further Assurances.    The parties hereto each agree to execute from time to time
such further documents as may be necessary to implement the terms of this Agreement. 

        The
parties hereto have executed this Amendment in multiple counterparts to be effective as of the Effective Date. 

Remainder of Page Intentionally Blank.

Signature Pages to Follow.  

17

 

	
 	
 	
BORROWER
	

 	
 	

MARKWEST HYDROCARBON, INC.
	

 	
 	

By:	
 	

 Gerald A. Tywoniuk

Senior Vice President, Finance
	

 	
 	
GUARANTORS
	

 	
 	

MARKWEST MICHIGAN, INC., a Colorado corporation
	

 	
 	

By:	
 	

 Gerald A. Tywoniuk

Vice President, Finance
	

 	
 	

MARKWEST RESOURCES, INC., a Colorado corporation
	

 	
 	

By:	
 	

 Gerald A. Tywoniuk

Vice President, Finance
	

 	
 	

WEST SHORE PROCESSING COMPANY, L.L.C., a Michigan limited liability company
	

 	
 	

By: Markwest Michigan, Inc., its Manager
	

 	
 	

By:	
 	

 
	 	 	 	 	

	 	 	Name:	 	 
	 	 	 	 	

	 	 	Title:	 	 
	 	 	 	 	

	

 	
 	

BASIN PIPELINE, L.L.C., a Michigan limited liability company
	

 	
 	

By: Markwest Michigan, Inc., its Manager
	

 	
 	

By:	
 	

 
	 	 	 	 	

	 	 	Name:	 	 
	 	 	 	 	

	 	 	Title:	 	 
	 	 	 	 	

18

 

	

 	
 	

MATREX, L.L.C., a Michigan limited liability company
	

 	
 	

By: Markwest Resources, Inc., its Manager
	

 	
 	

By:	
 	

 
	 	 	 	 	

	 	 	Name:	 	 
	 	 	 	 	

	 	 	Title:	 	 
	 	 	 	 	

	

 	
 	

MARKWEST ENERGY APPALACHIA, L.L.C., a Delaware limited liability company
	

 	
 	

By: MarkWest Hydrocarbon, Inc., a Delaware corporation, its sole member
	

 	
 	

By:	
 	

 
	 	 	 	 	

	 	 	Name:	 	 
	 	 	 	 	

	 	 	Title:	 	 
	 	 	 	 	

	

 	
 	

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

 	
 	

By:	
 	

 Richard L. Stein

Vice President
	

 	
 	

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

 	
 	

By:	
 	

 
	 	 	 	 	

	 	 	Name:	 	 
	 	 	 	 	

	 	 	Title:	 	 
	 	 	 	 	

19FIRST AMENDMENT TO CREDIT AGREEMENT  

        THIS FIRST AMENDMENT TO CREDIT AGREEMENT (this "Amendment") is entered into as of March 29, 2002, among
MARKWEST RESOURCES CANADA CORP. (previously known as MarkWest Acquisitions Corp.), an Alberta corporation (the "Borrower"), the undersigned Guarantors
(the "Guarantors"), BANK OF AMERICA, N.A. [acting through its Canadian branch], successor to Bank of America Canada, as Canadian
Administrative Agent (the "Administrative Agent") for the Lenders parties to the hereinafter defined
Credit Agreement, and the undersigned Lenders. 

        Reference
is made to the Credit Agreement dated as of October 12, 2001, (the "Credit Agreement") among Borrower, Administrative
Agent, and the Lenders parties thereto. Unless otherwise defined in this Amendment, capitalized terms used herein shall have the meaning set forth in the Credit Agreement; all section and
schedule references herein are to sections and schedules in the Credit Agreement; and all paragraph references herein are to paragraphs in this Amendment. 

RECITALS  

        A.    On the Effective Date as herein defined and immediately prior to the effectiveness of this Amendment, Bank of America,
N.A. [acting through its Canadian branch], is assigning a portion of its Commitment and its Loans to Royal Bank of Canada pursuant to a Lender Assignment Agreement. 

        B.    The Borrower has requested certain amendments to the Credit Agreement in order to, among other things, (i) decrease
the amount of the facility, (ii) add a borrowing base, and (iii) amend certain financial covenants. 

        C.    Subject to the terms and conditions of this Amendment, the Administrative Agent and the undersigned Lenders are willing to
agree to such amendments. 

        Accordingly,
for adequate and sufficient consideration, the parties hereto agree, as follows: 

 Paragraph 1. Amendments.  

        1.1  Definitions. 

        (a)  The
definition of "Applicable Margin" is amended in its entirety to read as follows: 

"Applicable Margin' means, with respect to any Loan of any type or any Letter of Credit, and at such time as the Leverage Ratio is in one of the
following ranges, the number of basis points ("b.p.") per annum for the relevant type of Loan, Commitment Fee or Letter of Credit and the relevant range
set forth below: 

	 
	 	 
	 	Applicable Margin

	Pricing

Level
	 	Leverage Ratio
	 	LIBO Rate Loan
	 	Letter of Credit
	 	Canadian

Prime Rate

Loan
	 	Commitment Fee

	1	 	Less than or equal to 1.0X	 	175.0 b.p.	 	175.0 b.p.	 	37.5 b.p.	 	25.0 b.p.
	2	 	Greater than 1.0X, but less than or equal to 2.0X	 	200.0 b.p.	 	200.0 b.p.	 	62.5 b.p.	 	30.0 b.p.
	3	 	Greater than 2.0X, but less than or equal to 2.75X	 	225.0 b.p.	 	225.0 b.p.	 	87.5 b.p.	 	37.5 b.p.
	4	 	Greater than 2.75X, but less than or equal to 3.25X	 	250.0 b.p.	 	250.0 b.p.	 	112.5 b.p.	 	50.0 b.p.
	5	 	Greater than 3.25X	 	275.0 b.p.	 	275.0 b.p.	 	137.5 b.p.	 	50.0 b.p.

The
Leverage Ratio shall be determined from the then most recent quarterly financial statements delivered by the Borrower pursuant to Section 7.1.1  and any changes in Applicable 

1

 

Margin shall become effective the first day of the third month following the date such financial statements are dated. In the event that the Borrower shall at any time fail to furnish the Lenders
such financial statements required to be delivered under Section 7.1.1, the maximum Applicable Margin and Commitment Fee as set forth above shall
apply until such time as such financial statements are so delivered. Changes in the Applicable Margin and Commitment Fee as a result of a change in the Leverage Ratio will occur automatically as
aforesaid without notice. The Applicable Margin and Commitment Fee shall be set at Pricing Level 4 for the period beginning on the Effective Date and ending on June 30, 2002,  unless during such
period the Leverage Ratio falls within Pricing Level 5, in which case Pricing Level 5 will apply." 

        (b)  The
following definition of "Available Borrowing Base" is inserted alphabetically into  Section 1.1: 

"Available Borrowing Base' means, at the particular time in question, the Canadian Borrowing Base in effect minus the Canadian Effective Amount at such
time." 

        (c)  The
following definition of "Borrowing Base Period" is inserted alphabetically into  Section 1.1: 

"Borrowing Base Period' means the period from March 29, 2002, to April 30, 2002, and each six-month period commencing
May 1, 2002, and each subsequent November 1 and May 1 thereafter." 

        (d)  The
following definition of "Canadian Borrowing Base" is inserted alphabetically into  Section 1.1: 

"Canadian Borrowing Base' means, if the U.S. Credit Agreement is effective, the Canadian Dollar Equivalent of the amount of the Global
Semi-Annual Borrowing Base allocated to the credit facilities hereunder pursuant to Section 2.1.3(b)(i), or, if the U.S. Credit
Agreement is not effective, the amount determined pursuant to Section 2.1.3(b)(ii), provided,  however,
in no event shall the Canadian Borrowing Base ever exceed the sum of the Revolving Loan Commitment Amount and Term Loans outstanding." 

        (e)  The
definition of "Canadian Dollar Equivalent" is hereby amended to read as follows: 

"Canadian
Dollar Equivalent' with respect to an amount denominated in U.S. Dollars (a) means, for all purposes other than the definition of "Canadian Borrowing Base' and  Section 2.1.3, the amount of the
Cdn. Dollars which would be required to purchase the relevant stated amount of U.S. Dollars based on an exchange
rate equal to 1.5657, and (b) means, for purposes of a Global Semi-Annual Borrowing Base determination pursuant to Section 2.1.3(a)  of the U.S. Credit Agreement, and for the purposes of the
definition of "Canadian Borrowing Base,' the amount of Cdn. Dollars which would be required to purchase the relevant
stated amount of U.S. Dollars based on the Noon Rate in effect on the effective date of the applicable Reserve Report." 

        (f)    The
following definition of "Canadian Effective Amount" is inserted alphabetically into  Section 1.1: 

"Canadian Effective Amount' means, on any date, the aggregate outstanding principal amount of all Loans after giving effect to any prepayments or
repayments of Loans occurring on such date plusthe Letter of Credit Outstandings." 

        (g)  The
definition of "Canadian Resident Lender" is amended by deleting the phrase "that is not" and replacing it with the
phrase "whose Canadian business income is not treated as income of". 

2

 

        (h)  The
definition of "Fixed Charge Coverage Ratio" is amended by (i) deleting the term "12 months" and
replacing it with the term "four Fiscal Quarters" and (ii) deleting each reference to the term "12-month" and replacing each such reference with the term "four-Fiscal
Quarter." 

        (i)    The
following definition of "Global Semi-Annual Borrowing Base" is inserted alphabetically in  Section 1.1: 

"Global Semi-Annual Borrowing Base' means, at the particular time in question, the amount provided for in  Section 2.1.3, provided, however, in no event
shall the Global Semi-Annual Borrowing Base ever exceed the sum of (i) the U.S. Dollar Equivalent of the Revolving Loan Commitment Amount plus the U.S. Dollar Equivalent of the Term
Loans outstanding hereunder and (ii) the Revolving Loan Commitment Amount and Terms Loans as defined in and outstanding under the U.S. Credit Agreement." 

        (j)    The
definition of "Letter of Credit Sublimit" is amended in its entirety to read as follows: "Letter of Credit Sublimit"
means the amount of Cdn. $7,828,500. 

        (k)  The
definition of "Leverage Ratio" is amended by (i) deleting the phrase "twelve most recently
ended months" and replacing it with the phrase "four Fiscal Quarters most recently ended" and (ii) deleting each reference to the term "12 months" and replacing each such
reference with the term "four Fiscal Quarters." 

        (l)    The
following definition of "Midstream Business" is inserted alphabetically into  Section 1.1.: 

"Midstream Business' means any and all operations of the Borrower and its Domestic Subsidiaries in Canada related to the gathering and processing of
natural gas and the fractionation, transportation, marketing, and storage of natural gas liquids." 

        (m)  The
following definition of "Midstream Business" is inserted alphabetically into  Section 1.1.: 

"Midstream Report' means a report, covering the Midstream Business, and any related non-Oil and Gas Properties businesses, prepared in
accordance with customary and prudent practices in form and substance acceptable to the Administrative Agent, setting forth (a) the total quantity of gas and liquids to be gathered, processed
and fractionated, (b) the estimated future net revenues and cumulative estimated future net revenues, (c) the present discounted value of future net revenues, and (d) such other
information and data with respect to the Midstream Business, and any related non-Oil and Gas Properties businesses, as the Administrative Agent may reasonably request." 

        (n)  The
definition of "Revolving Loan Commitment Amount" is amended by deleting the phrase "the Canadian Dollar Equivalent of
U.S. $35,000,000" and replacing such phrase with the term "Cdn. $54,799,500." 

        (o)  The
following definition of "U.S. Borrowing Base" is inserted alphabetically in  Section 1.1: 

"U.S. Borrowing Base' means the sum of (i) the Global Semi-Annual Borrowing Base allocated to the credit facilities governed by the
U.S. Credit Agreement pursuant to Section 2.1.3 thereof and (ii) the U.S. Monthly Borrowing Base (as defined in the U.S. Credit
Agreement), provided, however, in no event shall the U.S. Borrowing Base ever exceed the sum of the
Revolving Loan Commitment Amount and the Term Loans outstanding under the U.S. Credit Agreement." 

        (p)  The
definition of "U.S. Dollar Equivalent" is hereby amended to read as follows: 

"U.S. Dollar Equivalent' with respect to an amount denominated in Cdn. Dollars (a) means, for purposes of the definition of Global Borrowing Base
and for purposes of a Global Semi-Annual Borrowing Base determination pursuant to Section 2.1.3(a) of the U.S. Credit 

3

 

Agreement, the amount of U.S. Dollars required to purchase the relevant stated amount of Cdn. Dollars based on the Noon Rate in effect on the effective date of the relevant Reserve Report and
(b) means, for all purposes other than those described in the foregoing clause (a), the amount of U.S. Dollars required to purchase the relevant stated amount of Cdn. Dollars based on
the Noon Rate in effect on the day of determination." 

        (q)  The
following definition of "U.S. Effective Amount" is inserted alphabetically into  Section 1.1: 

"U.S. Effective Amount' means, on any date, the aggregate outstanding principal amount of all Loans under the U.S. Credit Agreement after giving effect
to any prepayments or repayments of such Loans occurring on such date plus the Letter of Credit Outstandings under the U.S. Credit Agreement." 

        1.2  Section 2.1.1(a). Section 2.1.1(a) is deleted in its
entirety and amended to read as follows: 

"(a) On
the terms and subject to the conditions hereof, each Lender severally, but not jointly, agrees to lend to the Borrower such Lender's Percentage of one or more Borrowings during the
Revolving Loan Availability Period, not to exceed such Lender's Percentage of the lesser of (i) the Revolving Loan Commitment Amount and (ii) the Canadian Borrowing Base." 

        1.3  Section 2.1.3.  Section 2.1.3 is deleted in its entirety and amended to read as
follows: 

"SECTION
2.1.3 Global Semi-Annual Borrowing Base Determinations and Allocations.

        (a)  Global Semi-Annual Borrowing Base and Canadian Borrowing Base Determinations.

        (i)    At
all times the U.S. Credit Agreement is effective, the Global Semi-Annual Borrowing Base will be governed by Section 2.1.3  of the U.S. Credit Agreement. 

        (ii)  If
the U.S. Credit Agreement is not effective, the Global Semi-Annual Borrowing Base will no longer be determined and the following provisions will govern
the determination of the Canadian Borrowing Base. At all times prior to the Revolving Loan Commitment Termination Date, the Canadian Effective Amount shall not exceed the Canadian Borrowing Base then
in effect. The Canadian Borrowing Base shall be redetermined for each Borrowing Base Period. The Canadian Borrowing Base shall be determined based upon the Oil and Gas Properties reflected in the most
recently delivered Reserve Report and the assets reflected in the most recently delivered Midstream Report and such credit and other factors (including, without limitation the assets, liabilities,
cash flow, business, properties, prospects, management and ownership of the Borrower and its Subsidiaries) as the Lenders deem relevant. The Lenders' determination of the Canadian Borrowing Base shall
be in each of their sole discretion, exercised in accordance with its standard and usual practice for determining borrowing base loans that it generally applies to borrowers in the oil and gas
business. On or before April 15 and October 15 of each year, the Canadian Administrative Agent shall recommend to the Lenders a new Canadian Borrowing Base, a copy of which
recommendation shall be provided concurrently to the Borrower. The Lenders shall, within fifteen (15) days of such recommendation (by unanimous agreement in the case of increasing the Canadian
Borrowing Base and by agreement of the Required Lenders in the case of maintaining or decreasing the Canadian Borrowing Base) inform the Canadian Administrative Agent in writing as to whether such
Lender agrees or disagrees with the Canadian Administrative Agent's recommendation. If a Lender disagrees, such notice shall contain the highest amount such Lender has approved for the Canadian
Borrowing Base. If at the end of such fifteen (15) day period any Lender has not communicated its approval or disapproval, such silence shall be deemed to be its approval. If the Canadian
Administrative Agent's recommended Canadian Borrowing 

4

 

Base is not approved or deemed approved as aforesaid by the Required Lenders at the end of such fifteen (15) day period, the Canadian Borrowing Base shall be the highest amount on which all of
the Lenders can agree if increasing the Canadian Borrowing Base or all of the Required Lenders can agree if maintaining or decreasing the Canadian Borrowing Base. After such redetermined Borrowing
Base is approved or otherwise determined as aforesaid, the Administrative Agent will notify the Borrower and the Lenders of the amount of the redetermined Canadian Borrowing Base, and such amount
shall become effective as to the next succeeding May 1 or November 1, as applicable. If the Borrower does not furnish the Reserve Reports or all such other information and data by the
date required, the Lenders may nonetheless determine a new Canadian Borrowing Base. It is expressly understood that the Lenders shall have no obligation to determine the Canadian Borrowing Base at any
particular amount, either in relation to the Commitment or otherwise. Promptly upon each redetermination of
the Canadian Borrowing Base pursuant to Section 2.1.3(a)(ii), the Canadian Administrative Agent shall notify the Borrower in writing of such
redetermination. 

        (b)  Special Semi-Annual Borrowing Base and Canadian Borrowing Base Determinations.

        (i)    At
all times the U.S. Credit Agreement is effective, Special Semi-Annual Borrowing Base Determinations (as defined in the U.S. Credit Agreement) will be
governed by Section 2.1.3(a)(iii) of the U.S. Credit Agreement. 

        (ii)  If
the U.S. Credit Agreement is not effective, Special Semi-Annual Borrowing Base Determinations (as defined in the U.S. Credit Agreement) will no longer be
made and the following provisions shall govern Special Canadian Borrowing Base Determinations (as hereinafter defined). In addition to the Canadian Borrowing Base determinations made pursuant to  Section 2.1.3(a)(ii)
, the Borrower and the Canadian Administrative Agent acting upon the direction of the Required Lenders may each request one
(1) additional Canadian Borrowing Base redetermination during each Borrowing Base Period (each such additional determination herein called a "Special Canadian Borrowing
Base Determination"). In the event the Borrower requests a Special Canadian Borrowing Base Determination pursuant to this  Section 2.1.3(b)(ii), the Borrower shall deliver
written notice of such request to the Lenders which shall include a Reserve Report prepared by
the Borrower as of a date not more than thirty (30) calendar days prior to the date of such request, for the benefit of the Lenders, and following receipt by the Canadian Administrative Agent
of such request, the Canadian Administrative Agent may request in writing other information prepared as of a date not more than thirty (30) calendar days prior to the date of such
request. Each Special Canadian Borrowing Base Determination shall be made pursuant to the procedures set forth in Section 2.1.3(a)(ii) and the
Canadian Administrative Agent shall give the Borrower notice of the redetermined Canadian Borrowing Base pursuant to Section 2.1.3(a)(ii)." 

        1.4.  Section 2.1.5.  Section 2.1.5 is amended by deleting each reference to the term
"Revolving Loan Commitment Amount" and replacing each such reference with the
term "Canadian Borrowing Base." 

        1.5  Section 2.1.6. Section 2.1.6 is
amended by (i) deleting the number "$20,000,000" and replacing it with the number "$10,000,000" and (ii) deleting the number "$110,000,000" and replacing it with the number
"$100,000,000." 

        1.6  Section 3.1(c). Section 3.1(c) is deleted in its entirety. 

        1.7  Section 3.1.2. Section 3.1.2 is deleted in its entirety and
amended to read as follows: 

        "SECTION
3.1.2 Mandatory Prepayment.

5

 

        (a)  Unless
otherwise directed by the Global Lenders (as defined in the U.S. Credit Agreement), if on any date the sum of the U.S. Dollar Equivalent of the Canadian Effective
Amount and the U.S. Effective Amount shall exceed the Global Borrowing Base, and no additional mandatory prepayments are made pursuant to Section 3.1.2  of the U.S. Credit Agreement to remedy any
remaining excess ("Unremedied Excess"), then the Borrower shall make mandatory
prepayments of Loans equal to such Unremedied Excess, and if any such Unremedied Excess remains after such prepayments, to the extent of such Unremedied Excess the Borrower shall immediately Cash
Collateralize the Reimbursement Obligations in an amount equal to the aggregate Stated Amount of all Letters of Credit outstanding and undrawn. The Borrower shall make fifty percent (50%) of such
payments within ninety (90) days following its receipt of the written notice of the Global Borrowing Base and Canadian Borrowing Base redetermination in accordance with  Section 2.1.3(a)(ii) of
the U.S. Credit Agreement, and the remaining fifty percent (50%) of such prepayments within one hundred eighty
(180) days following its receipt of the notice of the relevant redetermination. 

        (b)  If
on any date the U.S. Credit Agreement is not effective and the Canadian Effective Amount shall exceed the Canadian Borrowing Base, then the Borrower shall make
mandatory prepayments of Loans equal to such excess, and if any such excess remains after such prepayments, to the extent of such excess the Borrower shall immediately Cash Collateralize the
Reimbursement Obligations in an amount equal to the aggregate Stated Amount of all Letters of Credit outstanding and undrawn. The Borrower shall be obligated to (A) make fifty percent (50%) of
such prepayments within ninety (90) days following its receipt of the written notice of the Canadian Borrowing Base redetermination in accordance with  Section 2.1.3(a), and the remaining fifty
percent (50%) of such prepayments within one hundred eighty (180) days following its receipt of
notice of the relevant redetermination, or (B) make such prepayment on the date of any Sale which results in a reduction in the Canadian Borrowing Base pursuant to  Section 7.2.9(b)."

        (c)  During
the Revolving Loan Availability Period, Loans prepaid pursuant to this Section 3.1.2 may be
re-borrowed to the extent the Canadian Borrowing Base subsequently is re-determined to a level that would allow such re-borrowing and the conditions to Borrowing
hereunder have been satisfied. 

        1.8  Section 3.3.2.  Section 3.3.2 is amended to add the following phrase immediately
prior to the period at the end of such section: 

        "and
if the U.S. Credit Agreement is not effective, to Administrative Agent, as an annual engineering fee, $5,000 on each April 30, commencing April 30, 2002, until the
Stated Maturity Date." 

        1.9  Section 7.1.1(c).  Section 7.1.1(c) is amended by deleting the term "month" and
replacing it with the term "Fiscal Quarter." 

        1.10 Section 7.1.1(k).  Section 7.1.1(k) is amended to read as follows: 

        "(k)(i) on
or before April 1, effective January 1, of each year, a Reserve Report prepared by an independent petroleum engineer acceptable to the Required Lenders
(the "Independent Engineer"), and annually commencing October 1, 2002, effective as of July 1 of each year, a Reserve Report prepared by
personnel of the Borrower, (ii) together with each Reserve Report, a certificate from an officer of the Borrower with principal responsibility for reserve engineering certifying that, to the
best of his knowledge: (A) the information contained in the Reserve Report has been prepared in accordance with customary and prudent practices in the petroleum engineering industry and
Financial Accounting Standards Board Statement 69 (or the Canadian equivalent thereof), (B) attached to the certificate is a schedule of the Oil and Gas Properties evaluated by such Reserve
Report that are subject to the Lien of the Collateral Documents; and 

6

 

(C) attached to the certificate is a list of all marketing agreements not cancelable on 60 days or less notice without penalty or detriment) for the sale of production at a fixed price
from the Borrower's or its Subsidiaries' Oil and Gas Properties (including, without limitation, calls on, or other rights to purchase, production whether or not the same are currently being
exercised), and (iii) on or before April 1 and October 1 of each year, effective as of January 1 and July 1 respectively, a Midstream Report prepared by personnel of
the Borrower and accompanied by a certificate of a technical officer of the Borrower certifying that, to the best of his knowledge, the information contained in the Midstream Report has been prepared
in accordance with customary and prudent practices in the petroleum engineering industry." 

        1.11 Section 7.1.8. Section 7.1.8 is amended to add the
following phrase immediately prior to the period at the end of subsections (a) and (b): 

",
provided, MarkWest Energy Partners, L.P., a Delaware limited partnership, and each of its Subsidiaries and MarkWest Energy GP, L.L.C., a Delaware
limited liability company, shall not be required to comply with this Section so long as the only assets of such entities are cash or Cash Equivalent Investments in an aggregate amount not to
exceed $5,000.00." 

        1.12 Section 7.2.2. Section 7.2.2 is amended by:
(i) deleting the term "the Canadian Dollar Equivalent of U.S. $2,700,000" and replacing it with the term "Cdn.. $4,227,390," and (ii) deleting the term "the Canadian Dollar Equivalent of
U.S. $10,000,000" and replacing it with the term "Cdn.. $15,657,000." 

        1.13 Section 7.2.4(a).  Section 7.2.4(a) is amended by (i) deleting each reference to
the term "calendar month" and replacing each such reference with the term
"Fiscal Quarter" and (ii) deleting the term "after Closing" and replacing it with the term "after July 1, 2001." 

        1.14 Section 7.2.4(b).  Section 7.2.4(b) is amended by deleting the term "calendar month" and
replacing it with the term "Fiscal Quarter." 

        1.15 Section 7.2.4(c).  Section 7.2.4(c) is deleted in its entirety and amended to read as
follows: 

        "(c) The
Parent's Leverage Ratio to be greater than the amounts set forth below as of the last day of each Fiscal Quarter ending during the following periods: 

	Maximum Leverage Ratio
 
	 	As of the Date of

each Fiscal Quarter Ending

as Set Forth Below

	4.00	 	12/31/01
	3.75	 	3/31/02
	3.50	 	6/30/02
	3.25	 	9/30/02
	3.00	 	12/31/02 and Fiscal Quarters ending thereafter"

        1.16 Section 7.2.4(d).  Section 7.2.4(d)is deleted in its entirety and amended to read as
follows: 

        "(d) The
Parent's Fixed Charge Coverage Ratio to be less than the amounts set forth below as of the last day of each Fiscal Quarter ending during the following periods: 

	Minimum Fixed Charge Coverage Ratio
 
	 	As of the Date of

each Fiscal Quarter Ending

as Set Forth Below

	1.40	 	12/31/01
	1.50	 	3/31/02 through 12/31/02
	1.75	 	3/31/03 and thereafter"

7

 

        1.17 Section 7.2.9(b). Section 7.2.9(b) is deleted in its
entirety and amended to read as follows: 

        "(b) The
Borrower will not, and will not permit any of its Subsidiaries to, sell, convey, contribute or transfer any asset (including, without limitation, any sale or assignment
with or without recourse of any receivable) except: (i) retirement of assets in the ordinary course of business; (ii) the sale of Oil and Gas production and sale of inventory in the
ordinary course of business, including in connection with hedge agreements or pursuant to long-term contracts; (iii) any conveyance or transfer by a Subsidiary of the Borrower to
the Borrower, or by a Subsidiary of the Borrower to a wholly owned Subsidiary of Borrower; (iv) transfers by the Borrower to a Subsidiary permitted by  Section 7.2.5; (v) transfers of
Hydrocarbon Interests which transfers constitute payments in kind pursuant to the Incentive Payments
Agreement; and (vi) any other sale, conveyance, contribution or transfer of any asset or assets other than accounts receivable (the transfers permitted pursuant to this clause (vi) being
referred to as a "Sale"), provided, any such Sales made since the date of the most recent Canadian
Borrowing Base redetermination exceeding, individually or in the aggregate, ten percent (10%) of the Canadian Borrowing Base then in effect, shall result in a review of the Canadian Borrowing Base as
provided in this Section. The Borrower shall give the Administrative Agent and the Global Lenders notice of any such proposed Sale not less than twenty (20) Business Days prior to the
anticipated closing date of the proposed Sale. The Administrative Agent shall, within ten (10) Business Days and utilizing the Reserve Report and Midstream Report delivered in connection with
the most recent redetermination of the Canadian Borrowing Base, and any other information deemed relevant by the Canadian Administrative Agent propose to the Global Lenders the amount of the Canadian
Borrowing Base to be in effect after such Sale. Thereafter, the Global Lenders shall have eight (8) Business Days to approve or object to such proposed amount; and any failure to object shall
be deemed to be an approval. In the event there is no approval or deemed approval, the Administrative Agent shall poll the Global Lenders to ascertain the greatest amount of the Canadian Borrowing
Base then acceptable to the Required Global Lenders and such amount shall be the amount of the Canadian Borrowing Base. The Administrative Agent shall give the Borrower and the Global Lenders notice
of the amount of the revised Canadian Borrowing Base, and, if the U.S. Credit Agreement is effective, the Borrower may reallocate the sum of the U.S. Semi-Annual Borrowing Base and the
revised Canadian Borrowing Base as provided in Section 2.1.3(a)(ii) of the U.S. Credit Agreement. If the U.S. Credit Agreement is not effective,
references in this paragraph to Administrative Agent shall mean Canadian Administrative Agent, Global Lenders shall mean Lenders, and Required Global Lenders shall mean Required Lenders.
Notwithstanding the foregoing, the Borrower shall not, nor shall the Borrower permit any of its Subsidiaries to, transfer any assets, other than the sale of Oil and Gas production and inventory and
payment of trade payables in the ordinary course of business pursuant to Section 7.2.9(b)(ii), to any Person pursuant to this  Section 7.2.9 if a
Default shall have occurred and be continuing or would otherwise be existing after, or result from, any such transfer." 

        1.18 Section 7.2.15. A new  Section 7.2.15 is hereby inserted to read as follows: 

"SECTION
7.2.15. Gas Imbalances, Take-or-Pay or Other Prepayments. The Borrower will not allow net gas imbalances in excess of
200,000 MMBTU of gas, take-or-pay or other prepayments with respect to the Oil and Gas Properties of the Borrower or its Subsidiaries that would require the Borrower or its
Subsidiaries to deliver Oil and Gas produced on Oil and Gas Properties at some future time without then or thereafter receiving full payment therefore." 

        1.19 Section 10.1(a).  Section 10.1(a) is amended by deleting the word "or" appearing
immediately before subclause (e) thereof and inserting the following phrase
immediately after such subclause (e): "or (f) increase the Canadian Borrowing Base pursuant to Section 2.1.3 of the U.S. Credit Agreement
without the consent of the Lenders or increase the Global Borrowing Base pursuant to Section 2.1.3 of 

8

 

the U.S. Credit Agreement without the consent of the Global Lenders (as defined in the U.S. Credit Agreement), provided, the Required Lenders may
maintain or decrease the Canadian Borrowing Base pursuant to Section 2.1.3 of the U.S. Credit Agreement and the Required Global Lenders (as
defined in the U.S. Credit Agreement) may maintain or decrease the Global Borrowing Base pursuant to Section 2.1.3." 

        1.20 Schedule V.  Schedule V to the Credit Agreement is hereby amended to read as set forth
in Schedule V
attached hereto. 

        1.21 Exhibit F. Exhibit F to the Credit Agreement is hereby
amended to read as Exhibit F attached hereto. 

        Paragraph 2. Effective Date.    Notwithstanding any contrary provision, this Amendment is not
effective until the date (the "Effective Date") the following conditions are satisfied. 

        (a)  The
Administrative Agent shall have received counterparts of this Amendment, executed by the Borrower, the Guarantors, and the Required Lenders. 

        (b)  The
Administrative Agent shall have received counterparts of the Guaranty (MarkWest Energy Appalachia, L.L.C.), the Pledge and Security Agreement (MarkWest Energy
Appalachia, L.L.C.), and the Acknowledgment of Pledge, each executed by MarkWest Energy Appalachia, L.L.C. and the related financing statement 

        (c)  The
Administrative Agent shall have received from the Borrower and each Guarantor a certificate dated as of the Effective Date of its secretary, assistant secretary,
manager or general partner as applicable (i) as to resolutions of its board of directors or managers or their equivalent authorizing the execution and performance of this Amendment, and
(ii) if the officer executing this Amendment is not named in the incumbency certificate delivered at the time of execution of the Credit Agreement, as to the incumbency and signature of said
officer. 

        (d)  The
Administrative Agent shall have received a legal opinion from counsel to the Borrower and each Guarantor as to the due authorization, execution and delivery of this
Amendment. 

        (e)  The
"Effective Date" shall occur simultaneously as defined in the First Amendment to the U.S. Credit Agreement. 

        (f)    Fees
and expenses required to be paid pursuant to Paragraph 5 of this Amendment have been paid to the extent invoiced prior to the Effective Date. 

        (g)  The
Administrative Agent shall have received such other assurances, certificates, documents and consents as the Administrative Agent may require. 

        Paragraph 3. Successor Canadian Administrative Agent.    Pursuant to  Section 9.4
of the Credit Agreement, Bank of America Canada has resigned as Canadian Administrative Agent and the Lenders hereby appoint Bank of
America, N.A. [acting through its Canadian branch], successor to Bank of America Canada as the successor Canadian Administrative Agent for the Lenders under the Credit
Agreement for all purposes of the Credit Agreement, the Intercreditor Agreement, the Notes and each other Loan Document. 

        Paragraph 4. Acknowledgment and Ratification.    As a material inducement to the Administrative
Agent and the Lenders to execute and deliver this Amendment, each of the Borrower and the Guarantors (a) consents to the agreements in this Amendment and (b) agrees and acknowledges that
the execution, delivery, and performance of this Amendment shall in no way release, diminish, impair, reduce, or otherwise affect the respective obligations of the Borrower or any Guarantor under the
Loan Documents to which it is a party, which Loan Documents shall remain in full force and effect, and all rights thereunder are hereby ratified and confirmed. 

9

 

        Paragraph 5. Representations.    As a material inducement to the Administrative Agent and the
Lenders to execute and deliver this Amendment, each of the Borrower and the Guarantors represents and warrants to the Administrative Agent and the Lenders that as of the Effective Date of this
Amendment and as of the date of execution of this Amendment, (a) all representations and warranties in the Loan Documents are true and correct in all material respects as though made on the
date hereof, except to the extent that any of them speak to a different specific date, and (b) no Default or Event of Default exists. 

        Paragraph 6. Expenses.    The Borrower shall pay within ten (10) days of demand all
reasonable costs, fees, and expenses paid or incurred by the Administrative Agent incident to this Amendment, including, without limitation, the fees and expenses of the Administrative Agent's counsel
in connection with the negotiation, preparation, delivery, and execution of this Amendment and any related documents and filing and recording costs, and costs of title insurance endorsements if
required. 

        Paragraph 7. Miscellaneous.    This Amendment is a "Loan
Document"referred to in the Credit Agreement. The provisions relating to Loan Documents in Article 10 of the Credit
Agreement are incorporated in this Amendment by reference. Unless stated otherwise (a) the singular number includes the plural and vice versa and
words of any gender include each other gender, in each case, as appropriate, (b) headings and captions may not be construed in interpreting provisions, (c) this Amendment must be
construed, and its performance enforced, under Alberta law and applicable Canadian federal law, (d) if any part of this Amendment is for any reason found to be unenforceable, all other portions
of it nevertheless remain enforceable, and (e) this Amendment may be executed in any number of counterparts with the same effect as if all signatories had signed the same document, and all of
those counterparts must be construed together to constitute the same document. 

        Paragraph 8. Entire Agreement.    This Amendment represents the final
agreement between the parties about the subject matter of this Amendment and may not be contradicted by evidence of prior, contemporaneous, or subsequent oral agreements of the parties. There are no
unwritten oral agreements between the parties.

        Paragraph 9. Parties.    This Amendment binds and inures to the benefit of the Borrower, the
Guarantors, the Administrative Agent, the Lenders, and their respective successors and assigns. 

        Paragraph 10. Further Assurances.    The parties hereto each agree to execute from time to time
such further documents as may be necessary to implement the terms of this Agreement. 

        The
parties hereto have executed this Amendment in multiple counterparts to be effective as of the Effective Date. 

Remainder of Page Intentionally Blank.

Signature Pages to Follow.  

10

 

	
 	
 	
BORROWER
	

 	
 	

MARKWEST RESOURCES CANADA CORP.
	

 	
 	

By:	
 	

 Gerald A. Tywoniuk

Vice President, Finance
	

 	
 	
GUARANTORS
	

 	
 	

MARKWEST RESOURCES, INC., a Colorado corporation
	

 	
 	

By:	
 	

 Gerald A. Tywoniuk

Senior Vice President, Finance
	

 	
 	

MARKWEST MICHIGAN, INC., a Colorado corporation
	

 	
 	

By:	
 	

 Gerald A. Tywoniuk

Senior Vice President, Finance
	

 	
 	

WEST SHORE PROCESSING COMPANY, L.L.C., a Michigan limited liability company
	

 	
 	

By: Markwest Michigan, Inc., its Manager
	

 	
 	

By:	
 	

 
	 	 	 	 	

	 	 	Name:	 	 
	 	 	 	 	

	 	 	Title:	 	 
	 	 	 	 	

	

 	
 	

BASIN PIPELINE, L.L.C., a Michigan limited liability company
	

 	
 	

By: Markwest Michigan, Inc., its Manager
	

 	
 	

By:	
 	

 
	 	 	 	 	

	 	 	Name:	 	 
	 	 	 	 	

	 	 	Title:	 	 
	 	 	 	 	

11

 

	

 	
 	

MATREX, L.L.C., a Michigan limited liability company
	

 	
 	

By: Markwest Resources, Inc., its Manager
	

 	
 	

By:	
 	

 
	 	 	 	 	

	 	 	Name:	 	 
	 	 	 	 	

	 	 	Title:	 	 
	 	 	 	 	

	

 	
 	

MARKWEST HYDROCARBON, INC.

a Delaware corporation
	

 	
 	

By:	
 	

 
	 	 	 	 	

	 	 	Name:	 	 
	 	 	 	 	

	 	 	Title:	 	 
	 	 	 	 	

	

 	
 	

MARKWEST CANADIAN MIDSTREAM SERVICES, INC. an Alberta corporation
	

 	
 	

By:	
 	

 
	 	 	 	 	

	 	 	Name:	 	 
	 	 	 	 	

	 	 	Title:	 	 
	 	 	 	 	

	

 	
 	

MARKWEST ENERGY APPALACHIA, L.L.C., a Delaware limited liability company
	

 	
 	

By: Markwest Hydrocarbon, Inc., a Delaware corporation, its sole member
	

 	
 	

By:	
 	

 
	 	 	 	 	

	 	 	Name:	 	 
	 	 	 	 	

	 	 	Title:	 	 
	 	 	 	 	

	

 	
 	

BANK OF AMERICA, N.A.

[acting through its Canadian branch], successor to Bank of America Canada, as Canadian Administrative Agent and as a Lender
	

 	
 	

By:	
 	

 
	 	 	 	 	

	 	 	Name:	 	 
	 	 	 	 	

	 	 	Title:	 	 
	 	 	 	 	

12

 

	

 	
 	

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

 	
 	

By:	
 	

 
	 	 	 	 	

	 	 	Name:	 	 
	 	 	 	 	

	 	 	Title:	 	 
	 	 	 	 	

13

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