Document:

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                                                                 Exhibit 10.16

                                  GENRAD, INC.
                               SEVERANCE AGREEMENT

         This is an AGREEMENT entered into between GenRad, Inc. (the "Company")
and Brian C. Quirk ("Executive") effective as of the 21st day of August, 1998.

         Executive is a key executive of the Company and a vital part of its
management. In consideration of Executive's continued employment with the
Company, the parties agree as follows:

         1. TERM; WINDOW PERIOD. The term during which this Agreement (the
"Agreement") will be in effect (the "Term of the Agreement") will begin on
August 21, 1998 (the "Effective Date") and, except as provided below, will
terminate on the date which is two years from the date the Company advises the
Executive in writing that it is terminating this Agreement. If a Change of
Control (as defined in Exhibit A) occurs during the Term of the Agreement, the
Agreement will remain in effect until all obligations hereunder have been
discharged. The period starting on the date of such a Change of Control and
ending on the third anniversary of the Change of Control will be a "Window
Period" during which special provisions of this Agreement will apply.

         2. POSITIONS AND DUTIES. Subject to the provisions of the Agreement:

              2.1 Executive will serve as Vice President, Manufacturing
Operations, of the Company with responsibilities consistent with these
positions.

              2.2 Executive will be a full-time employee of the Company and,
except for reasonable work-related travel, will perform his duties at the
Company's headquarters location or, if different, the location at which he now
principally performs his employment duties for the Company.

              2.3 Executive will devote his entire business time and attention
and his best efforts to the duties and services of his positions. However,
Executive may serve on boards of directors of other businesses and attend to
personal investments and community and charitable service, provided that such
activities are not competitive with the business of the Company and do not
interfere with the performance of Executive's duties to the Company.

         3. COMPENSATION AND BENEFITS. During the term of the Agreement, the
Company will provide compensation and benefits to Executive as follows:

              3.1 BASE SALARY. Executive's base salary as of the Effective Date
will be $150,000 per year, payable in accordance with the applicable payroll
practices of the Company. The company will review Executive's base salary
annually, and Executive will receive such increases in base salary, if any, for
each succeeding year as the Board of

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                                                             Severance Agreement
                                                                    Page 2 of 10

Directors of the Company (the "Board") determines in its sole discretion.
Executive's Base Salary will not be decreased during the Term of the Agreement
except as part of a general reduction in which the base salaries of all
corporate officers of the Company have been decreased and will not be decreased
during a Window Period without Executive's prior written agreement.

              3.2 PERFORMANCE BONUS. Executive will be eligible for an annual
performance bonus. Executive's bonus for any year ending during a Window Period
will not be less than 100 percent of his bonus for the completed year
immediately preceding the Change of Control.

              3.3 OTHER BENEFITS. Executive will be entitled to participate in
all policies and arrangements (or in any successor or supplemental plans,
policies or arrangements) generally made available to officers of the Company.
Such benefits shall not be reduced during the Window Period.

         4. TERMINATION OF EMPLOYMENT; Severance Benefits.

              4.1 TERMINABILITY OF EMPLOYMENT. Either the Company or Executive
may at any time terminate Executive's employment with the Company after giving
30 days' written notice to the other party. However, if Executive's employment
terminates during the Term of the Agreement, the parties will be required to
discharge the applicable obligations described in this Section 4 and elsewhere
in this Agreement. If Executive's employment terminates at any time other than
during the Term of the Agreement, Executive will have no rights under the
Agreement.

              4.2 TERMINATION UPON DEATH OR DISABILITY. If Executive ceases to
be an employee of the Company as a result of death or disability, the Executive
will be entitled to receive the severance benefits set forth in Section 4.4.
However, nothing in this Agreement is intended to interfere with the rights of
Executive and his family or beneficiaries under other applicable plans, policies
or arrangements of the Company. For purposes of this Section 4.2, the Company
may terminate Executive's employment for "disability" if, because of physical or
mental incapacity, Executive is unable for a period of 30 consecutive days to
perform each of the material duties of his position and if determined by a
qualified physician chosen by the Company (and, if during a Window Period,
approved by the Executive or his conservator) to be probable that such
incapacity will continue for an additional 60 consecutive days.

              4.3 TERMINATION BY THE COMPANY FOR CAUSE OR BY EXECUTIVE WITHOUT
GOOD REASON. If the Company terminates Executive's employment for Cause (as
defined in this Section 4.3) or if Executive terminates his employment other
than for Good Reason (as defined in Section 4.4), the Company will have no
further obligation or liability to Executive hereunder other than for Base
Salary earned and unpaid at the time of

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                                                             Severance Agreement
                                                                    Page 3 of 10

termination and compensation for accrued vacation, and the term of the Agreement
will end when those amounts are paid.

              "Cause" mean (a) willful malfeasance or gross negligence in the
performance by Executive of his duties, resulting in harm to the Company, (b)
fraud or dishonesty by Executive with respect to the Company, or (c) Executive's
conviction of a felony.

              4.4  BY THE COMPANY WITHOUT CAUSE OR BY EXECUTIVE FOR GOOD REASON.

                      (a) ENTITLEMENT TO SEVERANCE BENEFITS. If, during the Term
              of the Agreement, the Company terminates Executive's employment
              without Cause, or if Executive terminates his employment for Good
              Reason, the Company will, subject to Section 5 below, provide
              severance benefits to Executive as set forth below in this Section
              4.4.

                      "Good Reason" means (i) failure by the Company to maintain
              Executive in the positions described in Section 2 or assignment to
              Executive of duties materially inconsistent with such positions,
              (ii) failure by the Company to provide Executive with the
              compensation and benefits described in Section 3, or (iii)
              relocation of Executive's principal place of work to a location
              more than 50 miles from the previous location.

                      (b) NORMAL SEVERANCE BENEFITS. Except as provided in
              paragraph (c), the Company will provide severance benefits as
              follows:

                              (i)   The Company will pay to Executive within 30
                                    days of the termination a lump-sum cash
                                    amount equal to one hundred percent (100%)
                                    of his annual Base Salary in effect at the
                                    time of his termination (or, if his Base
                                    Salary has been reduced within 60 days of
                                    the termination, his Base Salary in effect
                                    prior to the reduction).

                              (ii)  The Company will continue for a period of
                                    one year from the date of termination to
                                    provide Executive with the benefits set
                                    forth in Section 3.3 above. To the extent
                                    that the Company is unable to provide such
                                    benefits to Executive under its existing
                                    plans and arrangements, it will pay
                                    Executive cash amounts equal to the cost the
                                    Company would have incurred to provide these
                                    benefits.

                              (iii) Notwithstanding any contrary provisions of
                                    the plans or arrangements under which they
                                    are granted, all options to purchase Company
                                    stock held by Executive will immediately
                                    become exercisable.

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                                                             Severance Agreement
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                      (c) SEVERANCE BENEFITS FOLLOWING A CHANGE OF CONTROL. If
              the termination occurs during a Window Period, the Company will,
              instead of the benefits prescribed in paragraph (b), provide
              severance benefits to Executive as follows:

                              (i)   The Company will pay to Executive within 30
                                    days of the termination a lump-sum cash
                                    amount equal to two hundred percent (200%)
                                    of the sum of (A) Executive's annual Base
                                    Salary in effect immediately prior to the
                                    termination (or, if his Base Salary has been
                                    reduced within 60 days of the termination or
                                    at any time after the Change of Control, his
                                    Base Salary in effect prior to the
                                    reduction), plus (B) an amount equal to the
                                    bonus earned by Executive for the fiscal
                                    year completed immediately prior to the
                                    termination.

                              (ii)  The Company will also pay to Executive
                                    within 30 days of the termination a pro-rata
                                    portion of his target bonus (provided for in
                                    Section 3.2 above) for the year of
                                    termination.

                              (iii) The Company will continue for a period of
                                    three years from the date of termination to
                                    provide Executive with the benefits set
                                    forth in Section 3.3 above. To the extent
                                    the Company is unable to provide such
                                    benefits to Executive under its existing
                                    plans and arrangements, it will either
                                    arrange to provide Executive with
                                    substantially similar benefits upon
                                    comparable terms or pay Executive cash
                                    amounts equal to Executive's cost of
                                    obtaining such benefits.

                              (iv)  Notwithstanding any contrary provisions of
                                    the plans or arrangements under which they
                                    are granted, all options to purchase Company
                                    stock held by Executive will immediately
                                    become exercisable.

         5. LIMITATIONS ON SEVERANCE BENEFITS.

              5.1 Except as provided in Section 5.2 below, the payments and
benefits to which Executive will be entitled under Section 4 of this Agreement
will be reduced to the extent necessary to prevent Executive from becoming
liable for the excise tax levied on certain "excess parachute payments" under
section 4999 of the Internal Revenue Code of

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                                                             Severance Agreement
                                                                    Page 5 of 10

1986, as amended (the "Code"). If a reduction is made under this Section 5.1,
Executive will have the right to determine which payments and benefits will be
reduced.

              5.2 The limitations of Section 5.1 will not apply if--

                        (i)  the present value, net of all federal, state and
                             other income and excise taxes, of all payments and
                             benefits to which Executive is entitled hereunder
                             without such limitations, exceeds

                        (ii) the present value, net of all federal, state and
                             other income and excise taxes, of all payments and
                             benefits to which Executive would be entitled
                             hereunder if such limitations applied.

              5.3 Determinations under this Section 5 will be made by the firm
of certified public accountants then serving as the Company's auditor unless
Executive has reasonable objections to the use of that firm, in which case the
determinations will be made by a comparable firm chosen by Executive after
consultation with the Company. The determinations of such firm will be binding
upon the Company and Executive.

         6. WITHHOLDING. All payments required to be made by the Company to
Executive under this Agreement will be subject to the withholding of such
amounts, if any, relating to tax and other payroll deductions as may be required
by law.

         7. FEES AND EXPENSES. In the event of Executive's termination of
employment during a Window Period, the Company will pay any and all fees and
expenses (including legal fees and other costs of arbitration or litigation)
that may be incurred by Executive in enforcing his rights under this Agreement.
If the termination of employment does not occur during a Window Period, the
Company will pay that amount of such fees and expenses that bears the same ratio
to the total fees and expenses as the dollar amount of payments and benefits
determined to be payable to Executive bears to the total dollar amount of
payments and benefits in dispute.

         8. NO DUTY TO MITIGATE. Benefits payable under this Agreement as a
result of termination of Executive's employment will be considered severance pay
in consideration of his past service and his continued service from the
Effective Date, and his entitlement thereto will neither be governed by any duty
to mitigate his damages by seeking further employment nor offset by any
compensation that he may receive from other employment.

         9. CONFIDENTIALITY AND EXCLUSIVITY. Executive agrees to maintain the
confidentiality of the Company's (and its related entities and projects) books,
records, financial information, technical information, business plans and/or
strategies, and other confidential matters unless required to make disclosure in
the performance of his duties for the Company or as a result of a legal
proceeding or other legally mandated cause. In the event of termination without
Good Reason by Executive, other than such a

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                                                             Severance Agreement
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termination occurring during a Window Period, Executive will not for one year
following termination act as an executive officer for any company that directly
competes against the Company. The parties recognize and agree that should the
Company be required to pursue a claim against Executive under this Section 9,
the Company will likely be required to seek injunctive relief as well as damages
at law. Accordingly, Section 11, Arbitration, will not apply to any action by
the Company against Executive for violation of this Section 9. Executive agrees
for purposes of any disputes arising under this Section 9 to submit to the
exclusive jurisdiction of the federal and state courts in the Commonwealth of
Massachusetts.

         10. INDEMNIFICATION. To the extent permitted by law, the Company will
defend, indemnify and hold Executive harmless from and against any and all
losses, liabilities, damages, expenses (including attorneys' fees and costs),
actions, causes of action or proceedings arising directly or indirectly from
Executive's performance of this Agreement or services as an employee of the
Company. Executive may retain his own counsel to defend himself in such actions,
and the Company will pay for the reasonable costs and expense of such counsel.
This indemnification is in addition to any right of indemnification to which
Executive may be entitled under the Company's Articles of Organization and
By-laws and any insurance policies that may be maintained by the Company.

         11. ARBITRATION. Except as otherwise provided in Section 9, any dispute
or controversy between the parties involving the construction or application of
any terms, covenants or conditions of this Agreement, or any claim arising out
of or relating to this Agreement, or any claim arising out of or relating to
Executive's employment by the Company that is not resolved within ten days by
the parties will be settled by arbitration in Boston, Massachusetts, in
accordance with the rules of the American Arbitration Association then in
effect, and judgment upon the award rendered by the arbitrator(s) may be entered
in any court having jurisdiction thereof. The Company and Executive agree that
the arbitrator(s) will have no authority to award punitive or exemplary damages
or so-called consequential or remote damages such as damages for emotional
distress. Any decision of the arbitrator(s) will be final and binding upon the
parties. Upon request, the arbitrator(s) shall submit written findings of fact
and conclusions of law. The parties agree and understand that they hereby waive
their rights to a jury trial of any dispute or controversy relating to the
matters specified above in this Section 11.

         12. RIGHTS OF SURVIVORS. If Executive dies after becoming entitled to
benefits under Section 4 following termination of employment but before all such
benefits have been provided, (a) all unpaid cash amounts will be paid to the
beneficiary that have been designated by Executive in writing (the
"beneficiary"), or if none, to Executive's estate, (b) all applicable insurance
coverage will be provided to Executive's family as though Executive had
continued to live, and (c) any stock options that become exercisable under
Section 4.4(b)(iii) or Section 4.4(iv) will be exercisable by the beneficiary,
or if none, the estate.

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                                                             Severance Agreement
                                                                    Page 7 of 10

         13. SUCCESSORS. This Agreement will inure to and be binding upon the
Company's successors. The Company will require any successor to all or
substantially all of the business and/or assets of the Company by sale, merger
or consolidation (where the Company is not the surviving corporation), lease or
otherwise, by agreement in form and substance satisfactory to Executive, to
assume this Agreement expressly. This Agreement is not otherwise assignable by
the Company.

         14. SUBSIDIARIES. For purposes of this Agreement, employment by a
corporation or other entity that is controlled directly or indirectly by the
Company will be deemed to be employment by the Company. Thus, references in the
Agreement to "Company" include such corporations or other entities where
appropriate in the context.

         15. AMENDMENT OR MODIFICATION; WAIVER. Except as provided in clause (1)
of Exhibit A, this Agreement may not be amended unless agreed to in writing by
Executive and the Company. No waiver by either party of any breach of this
Agreement will be deemed a waiver of a subsequent breach.

         16. SEVERABILITY. In the event that any provision of this Agreement is
determined to be invalid or unenforceable, the remaining provisions shall remain
in full force and effect to the fullest extent permitted by law.

         17. CONTROLLING LAW. This Agreement will be controlled and interpreted
pursuant to Massachusetts law without regard to the conflict of laws principles
thereof.

         18. SUPERSEDED AGREEMENT. This Agreement supersedes any prior or
contemporaneous agreement between the parties with respect to the subject matter
hereof.

         19. NOTICES. Any notices required or permitted to be sent under this
Agreement are to be delivered by hand or mailed by registered or certified mail,
return receipt requested, and addressed as follows:

              IF TO THE COMPANY:

              GenRad, Inc.
              7 Technology Park Drive
              Westford, MA  01886-0033
              Attn:  President

              IF TO EXECUTIVE:

              Brian C. Quirk
              48 Audrey Road
              Belmont, MA 02178

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                                                             Severance Agreement
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         Either party may change its address for receiving notices by giving
notice to the other party.

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

                                          ---------------------------------
                                          Brian C. Quirk

                                          GENRAD, INC.

                                          By________________________________
                                            Jim F. Lyons
                                            Its President

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                                                             Severance Agreement
                                                                    Page 9 of 10

                                    EXHIBIT A

         "Change of Control" means the occurrence of any of the following
events:

                  (1) any Person becomes the owner of 20% or more of the
         Company's Common Stock; provided, however, that the Board of Directors
         of the Company may unilaterally amend this clause (1) to increase the
         20% threshold to any percentage up to, but not exceeding, 50%; or

                  (2) individuals who, as of the Effective Date, constitute the
         Board of Directors of the Company (the "Continuing Directors") cease
         for any reason to constitute at least a majority of such Board;
         provided, however, that any individual becoming a director after the
         Effective Date whose election or nomination for election by the
         Company's shareholders was approved by a vote of at least a majority of
         the Continuing Directors will be deemed to be a Continuing Director,
         but excluding for this purpose any such individual whose initial
         assumption of office occurs as a result of either an actual or
         threatened election contest (as such terms are used in Rule 14a-11 of
         Regulation 14A promulgated under the Securities and Exchange Act of
         1934 (the "Exchange Act")) or other actual or threatened solicitation
         of proxies or consents by or on behalf of a Person other than the
         Board; or

                  (3) approval by the shareholders of the Company of a
         reorganization, merger, consolidation or other transaction that will
         result in the transfer of ownership of more than 50% of the Company's
         Common Stock; or

                  (4) liquidation or dissolution of the Company or sale of
         substantially all of the Company's assets.

         In addition, for purposes of this definition the following terms have
the meanings set forth below:

         "Common Stock" means the then outstanding Common Stock of the Company
plus, for purposes of determining the stock ownership of any Person, the number
of unissued shares of Common Stock which such Person has the right to acquire
(whether such right is exercisable immediately or only after the passage of
time) upon the exercise of conversion rights, exchange rights, warrants or
options or otherwise. Notwithstanding the foregoing, the term "Common Stock"
does not include shares of preferred stock or convertible debt or options or
warrants to acquire shares of Common Stock (including any shares of Common Stock
issued or issuable upon the conversion or exercise thereof) to the extent that
the Board expressly so determines in any future transaction or transactions.

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                                                             Severance Agreement
                                                                   Page 10 of 10

         A Person will be deemed to be the "owner" of any Common Stock of which
such Person would be the "beneficial owner", as such term is defined in Rule
13d-3 promulgated by the Securities and Exchange Commission under the Exchange
Act.

         "Person" has the meaning used in Section 13(d) of the Exchange Act,
except that "Person" does not include (i) the Employee, an Employee Related
Party, or any group of which the Employee or Employee Related Party is a member,
or (ii) the Company or a wholly-owned subsidiary of the Company or an employee
benefit plan (or related trust) of the Company or of a wholly-owned subsidiary.

         An "Employee Related Party" means any affiliate or associate of the
Employee other than the Company or a subsidiary of the Company. The terms
"affiliate" and "associate" have the meanings given in Rule 12b-2 under the
Exchange Act; the term "registrant" in the definition of "associate" means, in
this case, the Company.<PAGE>

                                                           EXHIBIT 10.8

                                                                [EXECUTION COPY]

=======================================================================

                                 FIRST AMENDMENT
                 TO SECOND AMENDED AND RESTATED CREDIT AGREEMENT

                            dated as of May 26, 2000

                                      among

                           MARKWEST HYDROCARBON, INC.,
                                as the Borrower,

                                       and

                    CERTAIN COMMERCIAL LENDING INSTITUTIONS,
                                 as the Lenders,

                                       and

                             BANK OF AMERICA, N.A.,
           as the Administrative and Syndication Agent for the Lenders

=======================================================================
<PAGE>

                                 FIRST AMENDMENT
                 TO SECOND AMENDED AND RESTATED CREDIT AGREEMENT

     THIS FIRST AMENDMENT TO SECOND AMENDED AND RESTATED CREDIT AGREEMENT, dated
as of May 26, 2000 (this "AMENDMENT"), is among MARKWEST HYDROCARBON, INC., a
Delaware corporation (the "BORROWER"), the various commercial lending
institutions as are or may become parties hereto (the "LENDERS"), and BANK OF
AMERICA, N.A., as the Administrative Agent and Syndication Agent for the Lenders
(in such capacity, "AGENT").

                              W I T N E S S E T H:

     1.   Borrower, Lenders and Agent have heretofore entered into that certain
Second Amended and Restated Credit Agreement, dated as of September 29, 1999
(the "CREDIT AGREEMENT").

     2.   The parties to the Credit Agreement intend to amend the Credit
Agreement to add additional Lenders as parties to the Credit Agreement and to
otherwise amend the Credit Agreement as follows:

     II.  AMENDMENTS TO CREDIT AGREEMENT.

     A.   SECTION 1.1 of the Credit Agreement is hereby amended by adding the
following definitions of "First Amendment", "Frac Spread", "Keep Whole Contract"
and "Siloam Plant" in appropriate alphabetical order:

     " "FIRST AMENDMENT" means that certain First Amendment to Second Amended
     and Restated Credit Agreement, dated as of May 26, 2000, among the
     Borrower, the Lenders, and the Agent."

     " "FRAC SPREAD" means the sum of (i) the sales price per gallon received by
     the Borrower and its Subsidiaries with respect to the sale of natural gas
     liquids produced at the Siloam Plant pursuant to Keep Whole Contracts LESS
     (ii) the cost per gallon of natural gas paid by the Borrower and its
     Subsidiaries with respect to the sale of natural gas liquids produced at
     the Siloam Plant pursuant to Keep Whole Contracts."

     " "KEEP WHOLE CONTRACT" means any contract which requires Borrower to
     replace the energy content for natural gas liquids extracted from gas
     received by Borrower from producers with natural gas."

     " "SILOAM PLANT" means the fractionation plant covered by the Siloam
     Mortgage."
<PAGE>

     B.   The definitions of "Conversion Date", "Lenders", "Reducing Loan
Commitment Amount", "Reducing Loan Commitment Termination Date", "Revolving Loan
Commitment Amount", "Revolving Loan Commitment Termination Date", and "Stated
Maturity Date" appearing in SECTION 1.1 of the Credit Agreement are hereby
amended in their entirety to the followings:

     " "CONVERSION DATE" means the date the initial Reducing Loan is made
     pursuant to the terms hereof which shall be December 31, 2002 if a
     Commitment Termination Event has not previously occurred."

     " "LENDERS" means each financial institution listed on the signature pages
     of the First Amendment, and each other financial institution that becomes a
     party to this Agreement."

     " "REDUCING LOAN COMMITMENT AMOUNT" means an amount equal to the lesser of
     (i) $65,000,000 or (ii) the aggregate amount of Revolving Loans outstanding
     on the Conversion Date, as such amount may be reduced from time to time
     pursuant to SECTION 2.2."

     " "REDUCING LOAN COMMITMENT TERMINATION DATE" means the earliest of (a)
     December 31, 2006; (b) the date on which the Reducing Loan Commitment
     Amount is terminated in full or reduced to zero pursuant to SECTION 2.2;
     and (c) the date on which any Commitment Termination Event occurs. Upon the
     occurrence of any event described in CLAUSE (b) or (c), the Revolving Loan
     Commitments shall terminate automatically and without any further action."

     " "REVOLVING LOAN COMMITMENT AMOUNT" means, on any date, $65,000,000, as
     such amount may be reduced from time to time pursuant to SECTION 2.2."

     " "REVOLVING LOAN COMMITMENT TERMINATION DATE" means the earliest of (a)
     December 31, 2002; (b) the date on which the Revolving Loan Commitment
     Amount is terminated in full or reduced to zero pursuant to SECTION 2.2;
     and (c) the date on which any Commitment Termination Event occurs. Upon the
     occurrence of any event described in CLAUSE (b) or (c), the Revolving Loan
     Commitments shall terminate automatically and without any further action."

     " "STATED MATURITY DATE"means (a) in the case of any Revolving Loan,
     December 31, 2002, (b) in the case of any Letter of Credit, December 31,
     2006 and (c) in the case of any Reducing Loan, December 31, 2006."

     C.   SECTION 3.1.4 of the Credit Agreement is hereby amended in its
entirety to the following:

                                       2
<PAGE>

     " SECTION 3.1.4. MANDATORY AS TO MANDATORY PREPAYMENT RATIO. In the event
     that the Borrower's Mandatory Prepayment Ratio is at any time greater than
     (i) for the period from May 26, 2000 through December 31, 2000, 4.00 to
     1.0, (ii) for the period from January 1, 2001 through December 31, 2001,
     3.50 to 1.0, and (iii) on or after January 1, 2002, 3.00 to 1.0, the
     Borrower shall be required to make a mandatory prepayment with respect to
     outstanding Loans in an amount equal to the amount necessary for the
     Borrower to return to compliance with the required Mandatory Prepayment
     Ratio (the "MPR AMOUNT"). Borrower shall have the option to make such
     mandatory prepayment of the MPR Amount either (a) immediately on the date
     of the Borrower's failure to comply with the Mandatory Prepayment Ratio or
     (b) in up to six (6) equal monthly installments with the first such
     mandatory prepayment being due immediately on the date of such non-
     compliance and, assuming that the Borrower remains out of compliance with
     the Mandatory Prepayment Ratio, each subsequent payment shall be due and
     payable to the Agent on the monthly anniversary of the Borrower's failure
     to comply with the Mandatory Prepayment Ratio."

     D.   SECTION 7.1.8 of the Credit Agreement is hereby amended in its
entirety to the following:

     " SECTION 7.1.8 COMPLIANCE WITH HEDGING POLICY. (a) Borrower shall at all
     times comply with, and perform any and all obligations and actions set
     forth in, the terms and provisions of the Hedging Policy.

          (b)  At all times during the 2000 calendar year, Borrower shall have
     entered into Hedging Agreements (the "FRAC SPREAD HEDGING AGREEMENTS") for
     the period from May 2000 through December 2000 satisfactory to the Agent,
     which together with actual results for the period from January 2000 through
     April 2000, result in Borrower having an expected average Frac Spread of at
     least $0.20 per gallon for the 2000 calendar year with respect to at least
     sixty percent (60%) of natural gas liquids volumes fractionated at the
     Siloam Plant pursuant to Keep Whole Contracts. Any certificate delivered by
     the Borrower pursuant to SECTION 7.1.1(c) and relating to the 2000 calendar
     year shall contain a representation by the Borrower that Borrower is in
     compliance with this SECTION 7.1.8 in all respects."

     E.   The Credit Agreement is hereby amended by replacing EXHIBIT X to the
Credit Agreement with EXHIBIT X to this First Amendment.

     F.   After giving effect to, and as of the date of, this Amendment, the
applicable "Percentage" for (i) Bank of America, N.A. shall be 38.46153846%,
(ii) U.S. Bank, National Association shall be 38.46153846%, and (iii) KeyBank
National Association shall be 23.07692308%.

                                       3
<PAGE>

     III. EFFECTIVENESS. This Amendment shall become effective as of the date
hereof when Agent shall have received:

     A.   Counterparts hereof duly executed by Borrower, the Lenders and Agent
          (or, in the case of any party as to which an executed counterpart
          shall not have been received, telegraphic, telex, or other written
          confirmation from such party of execution of a counterpart hereof by
          such party);

     B.   Notes of even date herewith payable to the order of each Lender duly
          executed by Borrower in the original principal amount of each Lender's
          Commitment;

     C.   The fees set forth in that certain Fee Letter of even date herewith
          between Borrower and Agent;

     D.   A mortgagee title policy insuring the properties covered by the Kenova
          Mortgage, in form and substance and from title companies satisfactory
          to the Agent; and

     E.   Satisfactory evidence that Borrower is in compliance with SECTION
          7.1.8(b) of the Credit Agreement.

Upon effectiveness of this Amendment, each Lender or Agent signatory to this
Amendment shall for all purposes be a Lender or an Agent, respectively, party to
the Credit Agreement as amended by this Amendment and any other Loan Documents
executed by the Lenders or the Agents, respectively, and shall have the rights
and obligations of a Lender or an Agent, respectively, under the Loan Documents
to the same extent as if they were originally parties to the Credit Agreement,
and no further consent or action by the Borrower, the Lenders or the Agent or
any other agent shall be required and the Banks shall have the Commitments set
forth in SECTION II.E of this Amendment.

     IV.  REAFFIRMATION OF REPRESENTATIONS AND WARRANTIES. To induce Lenders and
Agent to enter into this Amendment, Borrower hereby reaffirms, as of the date
hereof, its representations and warranties in their entirety contained in
ARTICLE VI of the Credit Agreement and in all other documents executed pursuant
thereto (except to the extent such representations and warranties relate solely
to an earlier date) and additionally represents and warrants as follows:

          (i)  Borrower is a corporation duly incorporated, validly existing and
     in good standing under the laws of its jurisdiction of incorporation and
     has all requisite authority, permits and approvals, and is in good standing
     to conduct its business in each jurisdiction in which its business is
     conducted.

          (ii) Borrower has the corporate power and authority and legal right to
     execute and deliver this Amendment and to perform its obligations
     hereunder. The execution and delivery by Borrower of this Amendment and the
     performance of its obligations hereunder have been duly authorized by
     proper corporate proceedings, and this Amendment and the

                                       4
<PAGE>

     Credit Agreement, as amended hereby, constitute the legal, valid and
     binding obligations of Borrower, enforceable against Borrower in accordance
     with their terms, except as enforceability may be limited by bankruptcy,
     insolvency or similar laws affecting the enforcement of creditors' rights
     generally.

          (iii) No Default or Event of Default has occurred and is continuing as
     of the date hereof.

          (iv) There has been no material adverse change (a) in the financial
     condition, operations, assets, businesses, properties or prospects of
     Borrower and its Subsidiaries from September 29, 1999, except as otherwise
     disclosed in compliance with Section 7.1.1 of the Credit Agreement, (b)
     affecting the rights and remedies of Lenders under and in connection with
     this Amendment and the Credit Agreement, as amended by this Amendment, or
     (c) in the ability of Borrower to perform its obligations under this
     Amendment or the Credit Agreement, as amended by this Amendment.

          (v)  There is no pending or, to the knowledge of Borrower, threatened
     litigation, action, proceeding, or labor controversy affecting Borrower or
     any of its Subsidiaries, or any of their respective properties, businesses,
     assets or revenues, which may materially adversely affect the financial
     condition, operations, assets, business, properties or prospects of
     Borrower or any Subsidiary or which purports to affect the legality,
     validity or enforceability of this Amendment, Credit Agreement, the Notes
     or any other Loan Document, except as disclosed in ITEM 6.7 ("Litigation")
     of the Disclosure Schedule to the Credit Agreement and as supplemented in
     the Borrower's monthly financial report delivered pursuant to Section
     7.1.1(a) of the Credit Agreement.

          (vi) Borrower has not amended its Hedging Policy dated as of January,
     2000, which is attached as EXHIBIT X to the Credit Agreement and to this
     Amendment, and such Hedging Policy is in full force and effect as of the
     date of this First Amendment.

     V.   DEFINED TERMS. Except as amended hereby, terms used herein when
defined in the Credit Agreement shall have the same meanings herein unless the
context otherwise requires.

     VI.  REAFFIRMATION OF CREDIT AGREEMENT. This Amendment shall be deemed to
be an amendment to the Credit Agreement, and the Credit Agreement, as amended
hereby, is hereby ratified, approved and confirmed in each and every respect.
All references to the Credit Agreement herein and in any other document,
instrument, agreement or writing shall hereafter be deemed to refer to the
Credit Agreement as amended hereby.

     VII. GOVERNING LAW. THIS AMENDMENT, THE CREDIT AGREEMENT, THE NOTES AND
EACH OTHER LOAN DOCUMENT SHALL EACH BE DEEMED TO BE A CONTRACT MADE UNDER AND
GOVERNED BY THE INTERNAL LAWS OF THE STATE OF NEW YORK. All obligations of the
Borrower and rights of Lenders and Agent and

                                       5
<PAGE>

any other holders of the Notes expressed herein shall be in addition to and not
in limitation of those provided by applicable law.

     VIII.  SEVERABILITY OF PROVISIONS. Any provision in this Amendment that is
held to be inoperative, unenforceable, or invalid in any jurisdiction shall, as
to that jurisdiction, be inoperative, unenforceable, or invalid without
affecting the remaining provisions in that jurisdiction or the operation,
enforceability, or validity of that provision in any other jurisdiction, and to
this end the provisions of this Amendment are declared to be severable.

     IX.  COUNTERPARTS. This Amendment may be executed in any number of
counterparts, all of which taken together shall constitute one agreement, and
any of the parties hereto may execute this Amendment by signing any such
counterpart.

     X.   HEADINGS. Article and section headings in this Amendment are for
convenience of reference only, and shall not govern the interpretation of any of
the provisions of this Amendment.

     XI. SUCCESSORS AND ASSIGNS. This Amendment shall be binding upon and inure
to the benefit of the parties hereto and their respective successors and
assigns.

     XII. NOTICE. THIS WRITTEN AMENDMENT TOGETHER WITH THE CREDIT AGREEMENT AND
THE OTHER LOAN DOCUMENTS REPRESENT THE FINAL AGREEMENT BETWEEN THE PARTIES 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.

                                       6
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed by their respective officers thereunto duly authorized as of the day
and year first above written.

                                   MARKWEST HYDROCARBON, INC.

                                   By:
                                      ----------------------------------
                                   Name: Gerry Tywoniuk
                                   Title: Vice President of Finance

                                      S-1
<PAGE>

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

                                   By:
                                      ----------------------------------
                                   Name:
                                   Title:

                                      S-2
<PAGE>

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

                                   By:
                                      ----------------------------------
                                   Name:
                                   Title:

                                      S-3
<PAGE>

                                   KEYBANK NATIONAL ASSOCIATION, as a Lender

                                   By:
                                      ----------------------------------
                                   Name:
                                   Title:

                                      S-4
<PAGE>

                                                                       EXHIBIT X

                                 HEDGING POLICY

                                [to be attached]

                               Exhibit X - Page 1

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00022-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00022-of-00352.parquet"}]]