Document:

<PAGE>

                                                                    EXHIBIT 10.2

                               FIRST AMENDMENT TO
                                CREDIT AGREEMENT

                                    between

                                DRIL-QUIP, INC.

                                      and

                     BANK ONE, TEXAS, NATIONAL ASSOCIATION

                                Effective as of
                                  May 26, 2000
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                               TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                        PAGE
                                                        ----
<C>       <S>                                           <C>
ARTICLE I. DEFINITIONS                                    1
   1.01   Terms Defined Above..........................   1
   1.02   Terms Defined in Agreement...................   1
   1.03   References...................................   1
   1.04   Articles and Sections........................   1
   1.05   Number and Gender............................   2
ARTICLE II. AMENDMENTS.................................   2
   2.01   Amendment of Section 1.2.....................   2
   2.02   Amendment of Section 2.9.....................   2
   2.03   Amendment of Exhibit I.......................   2
ARTICLE III. CONDITIONS................................   3
   3.01   Receipt of Documents.........................   3
   3.02   Accuracy of Representations and Warranties...   3
   3.03   Matters Satisfactory to Lender...............   3
ARTICLE IV. REPRESENTATIONS AND WARRANTIES.............   3
ARTICLE V. RATIFICATION................................   3
ARTICLE VI. MISCELLANEOUS..............................   3
   6.01   Scope of Amendment...........................   3
   6.02   Agreement as Amended.........................   4
   6.03   Parties in Interest..........................   4
   6.04   Rights of Third Parties......................   4
   6.05   ENTIRE AGREEMENT.............................   4
   6.06   GOVERNING LAW................................   4
   6.07   JURISDICTION AND VENUE.......................   4
</TABLE>

                                       i
<PAGE>

                      FIRST AMENDMENT TO CREDIT AGREEMENT

        This FIRST AMENDMENT TO CREDIT AGREEMENT (this "First Amendment") is
made and entered into effective as of May 26, 2000, between DRIL-QUIP, INC., a
Delaware corporation (the "Borrower"), and BANK ONE, TEXAS, NATIONAL
ASSOCIATION, a national banking association (the "Lender"),

                                  WITNESSETH:

        WHEREAS, the above named parties did execute and exchange counterparts
of that certain Credit Agreement dated August 27, 1999 (the "Agreement"), to
which reference is here made for all purposes;

        WHEREAS, the parties subject to and bound by the Agreement are
desirous of amending the Agreement in the particulars hereinafter set forth;

        NOW, THEREFORE, in consideration of the mutual covenants and
agreements of the parties to the Agreement, as set forth therein, and the mutual
covenants and agreements of the parties hereto, as set forth in this First
Amendment, the parties hereto agree as follows:

                                  ARTICLE I.
                                  DEFINITIONS

        1.01 Terms Defined Above. As used herein, each of the terms "Agreement,"
"Borrower," "First Amendment," and "Lender" shall have the meaning assigned to
such term hereinabove.

        1.02 Terms Defined in Agreement. As used herein, each term defined in
the Agreement shall have the meaning assigned thereto in the Agreement, unless
expressly provided herein to the contrary.

        1.03 References. References in this First Amendment to Article or
Section numbers shall be to Articles and Sections of this First Amendment,
unless expressly stated herein to the contrary. References in this First
Amendment to "hereby," "herein," "hereinafter," "hereinabove," "hereinbelow,"
"hereof," and "hereunder" shall be to this First Amendment in its entirety and
not only to the particular Article or Section in which such reference appears.

        1.04 Articles and Sections. This First Amendment, for convenience only,
has been divided into Articles and Sections and it is understood that the
rights, powers, privileges, duties, and other legal relations of the parties
hereto shall be determined from this First Amendment as an entirety and without
regard to such division into Articles and Sections and without regard to
headings prefixed to such Articles and Sections.

        1.05 Number and Gender. Whenever the context requires, reference herein
made to the single number shall be understood to include the plural and likewise
the plural shall be understood to include the singular. Words denoting sex shall
be construed to include the masculine, feminine, and neuter, when such
construction is appropriate, and specific enumeration

                                       1
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shall not exclude the general, but shall be construed as cumulative. Definitions
of terms defined in the singular and plural shall be equally applicable to the
plural or singular, as the case may be.

                                  ARTICLE II.
                                  AMENDMENTS

        The Borrower and the Lender hereby amend the Agreement in the following
particulars:

        2.01 Amendment of Section 1.2. Section 1.2 of the Agreement is hereby
amended as follows:

          The following definitions are added or amended to read as follows:

               "Applicable Margin" shall mean as to each LIBO Rate Loan, one and
          three-quarters percent (1.75%)."

               "Available Commitment" shall mean, at any time, an amount equal
          to the remainder, if any, of (a) $30,000,000 minus (b) the Loan
          Balance at such time."

               "Commitment Termination Date" shall mean June 30, 2003."

               "Final Maturity" shall mean June 30, 2003."

        2.02 Amendment of Section 2.9. Section 2.9 of the Agreement is hereby
amended to read as follows:

               "2.9  Facility Fee.  In addition to interest on the Note as
          provided herein and all other fees payable hereunder and to compensate
          the Lender for the costs of the extension of credit hereunder, the
          Borrower shall pay to the Lender on the date of execution of this
          First Amendment, in immediately available funds, a facility fee in the
          amount of $50,000."

        2.03 Amendment of Exhibit I. Exhibit I, i.e. the Form of Promissory
Note, is as set forth on Exhibit I to this First Amendment.

                                 ARTICLE III.
                                  CONDITIONS

          The obligation of the Lender to amend the Agreement as provided herein
is subject to the fulfillment of the following conditions precedent:

        3.01 Receipt of Documents. The Lender shall have received, reviewed, and
approved the following documents and other items, appropriately executed when
necessary and in form and substance satisfactory to the Lender:

        (a) multiple counterparts of this First Amendment as requested by the
     Lender;

                                       2
<PAGE>

        (b)  the Note; and

        (c)  such other agreements, documents, items, instruments, opinions,
     certificates, waivers, consents, and evidence as the Lender may reasonably
     request.

        3.02 Accuracy of Representations and Warranties. The representations and
Warranties contained in Article IV of the Agreement and this First Amendment
shall be true and correct.

        3.03 Matters Satisfactory to Lender. All matters incident to the
consummation of the transactions contemplated hereby shall be satisfactory to
the Lender.

                                  ARTICLE IV.
                         REPRESENTATIONS AND WARRANTIES

          The Borrower hereby expressly remakes, in favor of the Lender, all of
the representations and warranties set forth in Article IV of the Agreement, and
represents and warrants that all such representations and warranties remain true
and unbreached.

                                  ARTICLE V.
                                 RATIFICATION

          Each of the parties hereto does hereby adopt, ratify, and confirm the
Agreement and the other Loan Documents, in all things in accordance with the
terms and provisions thereof, as amended by this First Amendment.

                                  ARTICLE VI.
                                 MISCELLANEOUS

        6.01 Scope of Amendment. The scope of this First Amendment is expressly
limited to the matters addressed herein and this First Amendment shall not
operate as a waiver of any past, present, or future breach, Default, or Event of
Default under the Agreement, except to the extent, if any, that any such breach,
Default, or Event of Default is remedied by the effect of this First Amendment.

        6.02 Agreement as Amended. All references to the Agreement in any
document heretofore or hereafter executed in connection with the transactions
contemplated in the Agreement shall be deemed to refer to the Agreement as
amended by this First Amendment.

        6.03 Parties in Interest. All provisions of this First Amendment shall
be binding upon and shall inure to the benefit of the Borrower, the Lender and
their respective successors and assigns.

        6.04 Rights of Third Parties. All provisions herein are imposed solely
and exclusively for the benefit of the Lender and the Borrower, and no other
Person shall have standing to require satisfaction of such provisions in
accordance with their terms and any or all of

                                       3
<PAGE>

such provisions may be freely waived in whole or in part by the Lender at any
time if in its sole discretion it deems it advisable to do so.

        6.05 ENTIRE AGREEMENT. THIS FIRST AMENDMENT CONSTITUTES THE ENTIRE
AGREEMENT BETWEEN THE PARTIES HERETO WITH RESPECT TO THE SUBJECT HEREOF AND
SUPERSEDES ANY PRIOR AGREEMENT, WHETHER WRITTEN OR ORAL, BETWEEN SUCH PARTIES
REGARDING THE SUBJECT HEREOF. FURTHERMORE IN THIS REGARD, THIS FIRST AMENDMENT,
THE AGREEMENT, THE NOTE, THE SECURITY INSTRUMENTS, AND THE OTHER WRITTEN
DOCUMENTS REFERRED TO IN THE AGREEMENT OR EXECUTED IN CONNECTION WITH OR AS
SECURITY FOR THE NOTE REPRESENT, COLLECTIVELY, THE FINAL AGREEMENT AMONG THE
PARTIES THERETO AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR,
CONTEMPORANEOUS, OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES. THERE ARE NO
UNWRITTEN ORAL AGREEMENTS AMONG THE PARTIES.

        6.06 GOVERNING LAW. THIS FIRST AMENDMENT, THE AGREEMENT AND THE NOTE
SHALL BE DEEMED TO BE CONTRACTS MADE UNDER AND SHALL BE CONSTRUED IN ACCORDANCE
WITH AND GOVERNED BY THE LAWS OF THE STATE OF TEXAS. THE PARTIES ACKNOWLEDGE AND
AGREE THAT THIS AGREEMENT AND THE NOTE AND THE TRANSACTIONS CONTEMPLATED HEREBY
BEAR A NORMAL, REASONABLE, AND SUBSTANTIAL RELATIONSHIP TO THE STATE OF TEXAS.

        6.07 JURISDICTION AND VENUE. ALL ACTIONS OR PROCEEDINGS WITH RESPECT
TO, ARISING DIRECTLY OR INDIRECTLY IN CONNECTION WITH, OUT OF, RELATED TO, OR
FROM THIS FIRST AMENDMENT, THE AGREEMENT OR ANY OTHER LOAN DOCUMENT MAY BE
LITIGATED IN COURTS HAVING SITUS IN HARRIS COUNTY, TEXAS. EACH OF THE BORROWER
AND THE LENDER HEREBY SUBMITS TO THE JURISDICTION OF ANY LOCAL, STATE, OR
FEDERAL COURT LOCATED IN HARRIS COUNTY, TEXAS, AND HEREBY WAIVES ANY RIGHTS IT
MAY HAVE TO TRANSFER OR CHANGE THE JURISDICTION OR VENUE OF ANY LITIGATION
BROUGHT AGAINST IT BY THE BORROWER OR THE LENDER IN ACCORDANCE WITH THIS
SECTION.

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<PAGE>

          IN WITNESS WHEREOF, this First Amendment to Credit Agreement is
executed effective the date first hereinabove written.

                            BORROWER:

                            DRIL-QUIP, INC.

                            By:    /s/ J. Mike Walker
                                 --------------------
                                 J. Mike Walker
                                 Co-Chairman

                            LENDER:

                            BANK ONE, TEXAS, NATIONAL ASSOCIATION

                            By:    /s/ Michelle A. Wolpert
                                 -------------------------
                                 Michelle A. Wolpert
                                 Vice President

                                       5
<PAGE>

                                   EXHIBIT I

                                  FORM OF NOTE

                                PROMISSORY NOTE

$30,000,000                      Houston, Texas                    May 26, 2000

          FOR VALUE RECEIVED and WITHOUT GRACE, the undersigned ("Maker")
promises to pay to the order of BANK ONE, TEXAS, NATIONAL ASSOCIATION
("Payee"), at its banking quarters in Houston, Harris County, Texas, the sum of
THIRTY MILLION DOLLARS ($30,000,000), or so much thereof as may be advanced
against this Note pursuant to the Credit Agreement dated of even date herewith
by and between Maker and Payee (as amended, restated, or supplemented from time
to time, the "Credit Agreement"), together with interest at the rates and
calculated as provided in the Credit Agreement.

          Reference is hereby made to the Credit Agreement for matters governed
thereby, including, without limitation, certain events which will entitle the
holder hereof to accelerate the maturity of all amounts due hereunder.
Capitalized terms used but not defined in this Note shall have the meanings
assigned to such terms in the Credit Agreement.

          This Note is issued pursuant to, is the "Note" under, and is payable
as provided in the Credit Agreement. Subject to compliance with applicable
provisions of the Credit Agreement, Maker may at any time pay the full amount or
any part of this Note without the payment of any premium or fee, but such
payment shall not, until this Note is fully paid and satisfied, excuse the
payment as it becomes due of any payment on this Note provided for in the Credit
Agreement.

          THIS NOTE SHALL BE GOVERNED AND CONTROLLED BY THE LAWS OF THE STATE OF
TEXAS WITHOUT GIVING EFFECT TO PRINCIPLES THEREOF RELATING TO CONFLICTS OF LAW;
PROVIDED, HOWEVER, THAT CHAPTER 345 OF THE TEXAS FINANCE CODE (WHICH REGULATES
CERTAIN REVOLVING CREDIT LOAN ACCOUNTS AND REVOLVING TRIPARTY ACCOUNTS) SHALL
NOT APPLY TO THIS NOTE.

                                    DRIL-QUIP, INC.

                                    By:
                                       ------------------------
                                       J. Mike Walker
                                       Co-Chairman

                                      I-1<PAGE>

                                THIRD AMENDMENT

     THIS THIRD AMENDMENT dated as of August 11, 2000 (this "Amendment") amends
the Second Amended and Restated Credit Agreement dated as of February 3, 1999
(as previously amended, the "Credit Agreement") among U S Liquids Inc. (the
"Company"), various financial institutions (the "Banks") and Bank of America,
N.A. (formerly known as Bank of America National Trust and Savings Association),
as Agent (in such capacity, the "Agent"). Terms defined in the Credit Agreement
are, unless otherwise defined herein or the context otherwise requires, used
herein as defined therein.

     WHEREAS, the Company, the Banks and the Agent have entered into the Credit
Agreement; and

     WHEREAS, the parties hereto desire to amend the Credit Agreement in certain
respects as more fully set forth herein;

     NOW, THEREFORE, the parties hereto agree as follows:

     SECTION 1  Amendments.  Subject to the satisfaction of the conditions
precedent set forth in Section 2, the Credit Agreement shall be amended as
follows.

     1.1  Deletion of Definition.  The definition of Bounce Back Event is
deleted from Section 1.1.

     1.2  Amendments to Definitions.  (a) The definition of "Commitment Amount"
is amended by deleting the reference to "$225,000,000" and substituting
"$150,000,000" therefor.

     (b) The definitions of "Funded Debt to EBITDA Ratio", "Interest Coverage
Ratio" and "Interest Expense" are amended in their entirety to read as follows,
respectively:

          Funded Debt to EBITDA Ratio means, at any time, the ratio of (a)
     Funded Debt at such time to (b) the total of (i) EBITDA for the Computation
     Period ending on the last day of the most recent Fiscal Quarter with
     respect to which the Company has delivered financial statements plus (ii)
     any Detroit Facility Reserve Charge taken during such Computation Period
     minus (iii) any Recoveries received (or, in the case of reversal of
     charges, taken) during such Computation Period minus (iv) any non-cash
     income resulting from the cancellation during such Computation Period of
     obligations of the Company to pay any amount to Waste Management, Inc. with
     respect to the Detroit Facility which was previously classified as a
     "contract reserve" on the Company's balance sheet; provided that clause (b)
     above shall be calculated for the period
<PAGE>

     ending (x) June 30, 2000 based upon the period of two consecutive Fiscal
     Quarters ending on such date and then multiplied by two and (y) September
     30, 2000 based upon the period of three consecutive Fiscal Quarters ending
     on such date and then multiplied by one and one-third.

          Interest Coverage Ratio means the ratio of (a) the total of (i)
     Consolidated Net Income before deducting Interest Expense and income tax
     expense for any Computation Period plus (ii) any Detroit Facility Reserve
     Charge taken during such Computation Period minus (iii) any Recoveries
     received (or, in the case of reversal of charges, taken) during such
     Computation Period minus (iv) any non-cash income resulting from the
     cancellation during such Computation Period of obligations of the Company
     to pay any amount to Waste Management, Inc. with respect to the Detroit
     Facility which was previously classified as a "contract reserve" on the
     Company's balance sheet plus (v) for any Fiscal Quarter ending on or prior
     to March 31, 2001, $428,000 to (b) Interest Expense for such Computation
     Period; provided that the Interest Coverage Ratio shall be calculated for
     the period ending (x) June 30, 2000 based upon the Fiscal Quarter ending on
     such date, (y) September 30, 2000 based upon the period of two consecutive
     Fiscal Quarters ending on such date and (z) December 31, 2000 based upon
     the period of three consecutive Fiscal Quarters ending on such date.

          Interest Expense means for any period the consolidated interest
     expense of the Company and its Subsidiaries for such period (including all
     imputed interest on Capital Leases); provided that for purposes of
     calculating the Interest Coverage Ratio, Interest Expense shall exclude
     amortization of deferred financing costs.

     1.3  Limitation on Total Outstandings.  Section 2.1.3 is amended in its
entirety to read as follows:

          2.1.3  Limitation on Total Outstandings.  Notwithstanding the
     foregoing provisions of this Section 2.1 or any other provision of this
     Agreement, Total Outstandings shall not exceed (1) $125,000,000 so long as
     the conditions in clause (2) or (3) below have not been satisfied; (2)
     $135,000,000 beginning on the date that the Company has delivered a
     compliance certificate showing (i) compliance with all financial covenants
     contained in Section 10.6 for the period ending September 30, 2000 and (ii)
     that EBITDA for the Company and its Subsidiaries on a consolidated basis
     (excluding any portion thereof attributable to acquisitions completed after
     December 31, 1999) equals or exceeds $10,942,000 for the fiscal quarter
     ended September 30, 2000, and (3) $150,000,000 so long as

                                       2
<PAGE>

     (i) either the conditions in clause (2) above have been satisfied or the
     Company has delivered a compliance certificate showing that EBITDA for the
     period of two consecutive Fiscal Quarters ending December 31, 2000
     (excluding any portion thereof attributable to acquisitions completed after
     December 31, 1999) equals or exceeds $22,107,000 and (ii) the Company has
     delivered a compliance certificate showing (x) compliance with all
     financial covenants contained in Section 10.6 for the period ending
     December 31, 2000 and (y) that EBITDA for the Fiscal Quarter ending
     December 31, 2000 (excluding any portion thereof attributable to
     acquisitions completed after December 31, 1999) equals or exceeds
     $11,165,000.

     1.4  Amendment to Section 10.6.3.  Section 10.6.3 is amended in its
entirety to read as follows:

          10.6.3  Funded Debt to EBITDA Ratio.  Not permit the Funded Debt to
     EBITDA Ratio as of the last day of any Fiscal Quarter to exceed (a) as of
     the last day of the Fiscal Quarter ending June 30, 2000, 3.30 to 1, (b) as
     of the last day of the Fiscal Quarters ending September 30, 2000 and
     December 31, 2000, 3.25 to 1.0, and (c) as of the last day of any Fiscal
     Quarter ending thereafter, 3.0 to 1.0.

     1.5  Amendment to Section 10.11. Clause (3)(i) of Section 10.11 is amended
by deleting the phrase "(or, if the maximum Total Outstandings permitted under
Section 2.1.3 is equal to or greater than $150,000,000, $5,000,000)".

     1.6  Amendment to Section 11.2.1.  Section 11.2.1 is amended by (a)
deleting the word "and" at the end of clause (b)(ii); (b) deleting the period at
the end of clause (c) and substituting a semi-colon followed by the word "and"
therefor; and (c) inserting the following new clause (d):

          (d)  after giving effect to the making of such Loan or the issuance of
     such Letter of Credit (and, in the case of the making of a Loan, the use of
     the proceeds thereof), the Funded Debt to EBITDA Ratio will not exceed (ii)
     at any time prior to September 30, 2000, 3.30 to 1, (ii) at any time
     March 31, 2001, 3.25 to 1.0, and (iii) at any time thereafter, 3.0 to 1.0.

     1.7  Amendment to Schedule 1.1.  Schedule 1.1 is amended in its entirety to
read as set forth on Schedule 1.1 hereto (and the revised pricing set forth
therein shall become effective on the date of the effectiveness of this
Amendment based upon the most recent financial statements delivered by the
Company as of such date, subject to adjustment as set forth in such Schedule).

                                       3
<PAGE>

     SECTION 2  Effectiveness.  The amendments set forth in Section 1 above
shall become effective when the Agent shall have received (i) counterparts of
this Amendment executed by the Company and the Required Banks, (ii) a
Confirmation, substantially in the form of Exhibit A, signed by the Company and
each Subsidiary, and (iii) an amendment fee for each Bank which, on or before
noon (Chicago time) on August 11, 2000, executes and delivers to the Agent (by
facsimile or otherwise) a counterpart hereof, such fee to be in an amount equal
to 0.125% of such Bank's Commitment after giving effect hereto.

     SECTION 3  Miscellaneous.

     3.1  Continuing Effectiveness, etc.  As herein amended, the Credit
Agreement shall remain in full force and effect and is hereby ratified and
confirmed in all respects.  After the effectiveness of this Amendment, all
references in the Credit Agreement and the other Loan Documents to "Credit
Agreement" or similar terms shall refer to the Credit Agreement as amended
hereby.

     3.2  Counterparts.  This Amendment may be executed in any number of
counterparts and by the different parties on separate counterparts, and each
such counterpart shall be deemed to be an original but all such counterparts
shall together constitute one and the same Amendment.

     3.3  Governing Law.  This Amendment shall be a contract made under and
governed by the laws of the State of Illinois applicable to contracts made and
to be performed entirely within such state.

     3.4  Successors and Assigns.  This Amendment shall be binding upon the
Company, the Banks and the Agent and their respective successors and assigns,
and shall inure to the benefit of the Company, the Banks and the Agent and the
respective successors and assigns of the Banks and the Agent.

                                       4
<PAGE>

     Delivered at Chicago, Illinois, as of the day and year first above written.

                              U S LIQUIDS INC.

                              By
                                 ------------------------------
                              Title
                                   ----------------------------

                              BANK OF AMERICA, N.A., as Agent

                              By
                                 ------------------------------
                              Title
                                   ----------------------------

                              BANK OF AMERICA, N.A., as a Bank

                              By
                                 ------------------------------
                              Title
                                   ----------------------------

                              FLEET NATIONAL BANK

                              By
                                 ------------------------------
                              Title
                                   ----------------------------

                              BANK ONE TEXAS, N.A.

                              By
                                 ------------------------------
                              Title
                                   ----------------------------

                                      S-1

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                              THE BANK OF NOVA SCOTIA

                              By
                                 ------------------------------
                              Title
                                   ----------------------------

                              UNION BANK OF CALIFORNIA

                              By
                                 ------------------------------
                              Title
                                   ----------------------------

                              COMERICA BANK

                              By
                                 ------------------------------
                              Title
                                   ----------------------------

                              WELLS FARGO BANK, N.A.

                              By
                                 ------------------------------
                              Title
                                   ----------------------------

                              BNP PARIBAS

                              By
                                 ------------------------------
                              Title
                                   ----------------------------

                              By
                                 ------------------------------
                              Title
                                   ----------------------------

                                      S-2

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