<PAGE>

                                                                   EXHIBIT 10.23

                      FOURTH AMENDMENT TO CREDIT AGREEMENT

         THIS FOURTH AMENDMENT TO CREDIT AGREEMENT (as same may be renewed,
extended, modified, restated amended and/or rearranged, the "Fourth Amendment")
dated as of April 30, 2002, is between MOUNTAIN COMPRESSED AIR, INC., a Texas
corporation (hereinafter referred to as "Borrower") and WELLS FARGO BANK TEXAS,
NATIONAL ASSOCIATION, a national banking association ("Bank").

                                    RECITALS:

         A. Bank and Borrower entered into that certain Credit Agreement dated
as of February 6, 2001 (the "Original Agreement"), as amended by that certain
First Amendment to Credit Agreement dated as of August 9, 2001 (the "First
Amendment"), as amended by that certain Second Amendment to Credit Agreement
dated as of November 30, 2001 (the "Second Amendment"), as amended by that
certain Third Amendment to Credit Agreement dated as of January 31, 2002 (the
"Third Amendment", together with the Original Agreement, the First Amendment and
the Second Amendment referred to hereafter as the Agreement).

         B. Borrower has requested that Bank extend the maturity date of the
Line of Credit Note from April 30, 2002 to April 30, 2003. Bank has agreed to do
so, subject to the terms and conditions contained herein.

         C. OilQuip Rentals, Inc., a Delaware corporation (the "Parent")
("OilQuip"), Munawar and Jayne Hidayatallah (the "Hidayatallahs") and
Allis-Chalmers Company, a Delaware corporation ("Allis-Chalmers") each
guaranteed to the Bank the payment and performance of certain indebtedness and
obligations of Borrower to Bank.

         D. Borrower and Bank now desire to enter into this Fourth Amendment on
the terms set forth herein.

         NOW, THEREFORE, in consideration of the premises herein contained and
other good and valuable consideration, the receipt and sufficiency of which are
hereby acknowledged, the parties hereto agree as follows:

                                    ARTICLE 1

                                  GENERAL TERMS

         Section 1.1 TERMS DEFINED IN AGREEMENT. As used in this Fourth
Amendment, except as may otherwise be provided herein, all capitalized terms
which are defined in the Agreement, as amended, have the same meaning herein as
therein, all of such terms and their definitions being incorporated herein by
reference.

<PAGE>

         Section 1.2 CONFIRMATION AND EXTENT OF CHANGES. All terms which are
defined or referred to in the Agreement shall remain unchanged except as
otherwise specifically provided in this Fourth Amendment. It is hereby confirmed
that the term "Agreement" includes the Agreement as amended by this Fourth
Amendment.

                                    ARTICLE 2

                                   AMENDMENTS

         Section 2.1 AMENDMENT TO SECTION 1.1(a). Effective as of the date
hereof, Section 1.1(a) of the Agreement is hereby amended to read in its
entirety as follows:

                  "(a) Line of Credit. Subject to the terms and conditions of
         this Agreement, Bank hereby agrees to make advances to Borrower (i)
         from January 16, 2002 up to and including March 30, 2002, not to exceed
         at any time the aggregate principal amount of Seven Hundred
         Seventy-Five Thousand and No/100 Dollars ($775,000.00) and (ii) from
         March 31, 2002 up to and including April 30, 2003 not to exceed the
         aggregate principle amount of Five Hundred Thousand and No/100 Dollars
         ($500,000) ("Line of Credit"), the proceeds of which shall be used to
         support working capital, issue letters of credit (with a $240,000.00
         sublimit), and general corporate purposes. Borrower's obligation to
         repay advances under the Line of Credit shall be evidenced by a
         promissory note substantially in the form of Exhibit A-1 attached
         hereto ("Line of Credit Note"), all terms of which are incorporated
         herein by this reference. If at any time (including, without
         limitation, March 31, 2002 and thereafter, when the Line of Credit
         automatically reduces to $500,000.00) the outstanding principal amount
         of the Line of Credit plus the sum of all outstanding Letters of Credit
         exceeds the then current Line of Credit, then the Borrower shall
         promptly prepay the outstanding Line of Credit in an aggregate
         principal amount equal to such excess, together with interest on the
         principal amount paid accrued to the date of such prepayment."

         Section 2.2 AMENDMENT TO SECTION 1.1(b). Effective as of the date
hereof, Section 1.1(b) of the Agreement is hereby amended to read in its
entirety as follows:

                  "(b) Limitation on Borrowings. Outstanding borrowings under
         the Line of Credit, to a maximum of the principal amount set forth
         above, shall not exceed an aggregate of (i) $775,000.00 from January
         16, 2002 through and including March 30, 2002, when combined with the
         undrawn Letters of Credit and (ii) $500,00.00 from March 31, 2002
         through and including April 30, 2003, when combined with the undrawn
         Letters of Credit (as hereinafter defined). All borrowings under the
         Line of Credit shall be in amounts of at least $10,000. There will be
         no minimum amount required on borrowings under the Line of Credit if
         borrowed through Bank's credit sweep product."

         Section 2.3 Section 2.4 AMENDMENT TO SECTION 4.9. Effective as of the
date hereof, Section 4.9 of the Agreement is hereby amended to read in its
entirety as follows:

                                       2
<PAGE>

                  "4.9 FINANCIAL CONDITION. (a) Maintain, or cause to be
         maintained, Borrower's financial condition as follows using generally
         accepted accounting principles consistently applied and used
         consistently with prior practices (except to the extent modified by the
         definitions herein):

                  (i) Beginning February 6, 2001, Tangible Net Worth not at any
         time less than eighty-five percent (85%) of Tangible Net Worth as of
         February 6, 2001 (plus seventy-five percent (75%) of cumulative net
         income after February 6, 2001, excluding any fiscal quarters in which
         net income is negative), plus one hundred percent (100%) of equity
         offerings after the date hereof, with "Tangible Net Worth" defined
         herein as the aggregate of total stockholders' equity plus the Seller
         Note less any intangible assets.

                  (ii) Fixed Charge Coverage Ratio not less than 1.1 to 1.0 for
         the twelve (12) month period ending on the last day of each fiscal
         quarter, beginning with the fiscal quarter ending March 31, 2001, with
         "EBITDA" defined herein as net income plus interest charges, plus
         taxes, plus depreciation, amortization and non-cash charges on a
         trailing twelve (12) month basis and with "Fixed Charge Coverage Ratio"
         defined herein as (i) EBITDA plus applicable operating lease payments
         less unfinanced capital expenditures divided by (ii) the aggregate of
         total interest charges (excluding any applicable paid-in-kind ("PIK")
         charges), scheduled principal payments, operating lease payments, cash
         dividends paid, and paid taxes for the same period. EBITDA will be
         computed on a trailing twelve (12) months basis. Through September 30,
         2001, fixed charges will be annualized. Thereafter, fixed charges will
         be on a trailing twelve-month basis.

                  (iii) Beginning December 31, 2001, Total Funded Debt to EBITDA
         Ratio not more than 4.50 to 1.00; not more than 4.00 to 1.00 for the
         period ending March 31, 2002; not more than 3.75 to 1.00 for the
         periods ending June 30, 2002 and September 30, 2002; not more than 2.50
         to 1.00 for the period ending December 31, 2002; and not more than 2.00
         to 1.00 thereafter with "Total Funded Debt to EBITDA Ratio" defined as
         Total Funded Debt divided by the twelve (12) trailing months EBITDA.
         "Total Funded Debt" is defined herein as all interest-bearing
         obligations of Borrower, whether secured or unsecured, senior or
         subordinated, excluding the Seller Note.

         (b) Maintain, or cause to be maintained, Allis-Chalmers' consolidated
Debt Service Coverage Ratio as of each date set forth below, determined for the
period beginning on April 30, 2002 and ending on such date, at not less than the
amount set forth opposite such date using generally accepted accounting
principles consistently applied and used consistently with prior practices:

                DATE                         MINIMUM DEBT SERVICE COVERAGE RATIO

         June 30, 2002                                    0.9 to 1
         September 30, 2002                               1.0 to 1
         December 31, 2002                                1.1 to 1

                                       3
<PAGE>

                  "Debt Service Coverage Ratio" for any period means the ratio
         of (i) the sum of (A)Funds From Operations and (B) Interest Expense
         MINUS (C) Capital Expenditures to (ii) the sum of (A) Current
         Maturities of Long Term Debt and (B) Interest Expense, each for such
         period. "Funds From Operations" for any person or entity for a given
         period means the sum of such person's or entity's Net Income, (ii)
         depreciation and amortization, (iii) deferred income taxes, and (iv)
         other non-cash items, each as determined for such period. "Interest
         Expense" means, for any person or entity, for a fiscal year-to-date
         period, such person's or entity's total gross interest expense during
         such period (excluding interest income), and shall in any event,
         include, without limitation (i) interest expensed (whether or not paid
         on all Debt, (ii) the amortization of debt discounts, (iii) the
         amortization of all fees payable in connection with the incurrence of
         Debt to the extent included in interest expense, and (iv) the portion
         of any capitalized lease obligation allocable to interest expense.
         "Capital Expenditures" for any period means any expenditure of money
         for the lease, purchase or other acquisition of any capital asset, or
         for the lease of any other asset whether payable currently or in the
         future. "Current Maturities of Long Term Debt" for any person or entity
         for any period means the amount of such person's or entity's long term
         debt and capitalized leases which became due during such period. "Net
         Income" means fiscal year-to-date after tax net income from continuing
         operations (after overhead allocations from Allis-Chalmers, if any),
         less any deferred income tax benefit. "Debt" means for any person or
         entity as of a given date, all items of indebtedness or liability which
         in accordance with generally accepted accounting principles would be
         included in determining total liabilities as shown on the liabilities
         side of a balance sheet for such person or entity and shall also
         included the aggregate payments required to be made by such person or
         entity at any time under any lease that is considered a capitalized
         lease under generally accepted accounting principles."

         Section 2.5 AMENDMENT TO SECTION 6.1(m). Effective as of the date
hereof, Section 6.1(m) shall be amended to read in its entirety as follows:

                  "(m) Borrower shall fail to deliver to the Bank on or before
         May 31, 2002, a fully executed subordination agreement in favor of the
         Bank in form and substance acceptable to the Bank in the Bank's sole
         discretion, executed by Borrower, Bank, the Hidayatallahs, Jens H.
         Mortensen, Wells Fargo Credit, Inc., Allis-Chalmers, Strata Directional
         Technology, Inc., Jens' Oil Field Service, Inc., and such other parties
         as the Bank requires."

                                    ARTICLE 3

                         REPRESENTATIONS AND WARRANTIES

         In order to induce the Bank to enter into this Fourth Amendment and to
continue to make the loans provided for in the Agreement, the Borrower
represents and warrants (which representations and warranties will survive the
execution and delivery hereof and will be deemed for all purposes to be
additional representations and warranties of the Agreement) that:

                                       4
<PAGE>

         Section 3.1 REPRESENTATIONS AND WARRANTIES OF THE AGREEMENT AND THE
LOAN DOCUMENTS. The representations and warranties of the Borrower contained in
the Agreement and the Loan Documents and otherwise made in writing by or on
behalf of the Borrower pursuant to the Agreement and the Loan Documents were
true and correct when made, and are true and correct in all material respects at
and as of the time of delivery of this Fourth Amendment, except for such changes
in the facts represented and warranted as are not in violation of the Agreement
and the Loan Documents.

         Section 3.2 COMPLIANCE WITH OBLIGATIONS. The Borrower has performed and
complied with all agreements and conditions contained in the Agreement and the
Loan Documents required to be performed or complied with by the Borrower prior
to or at the time of delivery of this Fourth Amendment.

         Section 3.3 DEFAULTS. There exists, and after giving effect to this
Fourth Amendment, will exist, no default or Event of Default, or any condition,
or act which constitutes, or with notice or lapse of time (or both) would
constitute an event of default under any loan agreement, note agreement, or
trust indenture to which the Borrower is a party.

         Section 3.4 NO AMENDMENTS. Nothing in Article 3 of this Fourth
Amendment is intended to amend any of the representations or warranties of the
Agreement.

                                    ARTICLE 4

                                   CONDITIONS

         The Bank has relied upon the representations and warranties contained
in this Fourth Amendment in agreeing to the amendments and supplements to the
Agreement set forth herein and the amendments and supplements to the Agreement
set forth herein are conditioned upon and subject to the accuracy of each and
every representation and warranty of the Borrower made or referred to herein, to
the performance by the Borrower of its obligations to be performed under the
Agreement and the Loan Documents on or before the date of this Fourth Amendment
and to the following further conditions:

         Section 4.1 THE NOTE. The Borrower shall have duly and validly issued,
executed and delivered to the Bank the Promissory Note in the form of EXHIBIT
"A-1" to this Fourth Amendment.

         Section 4.2 OFFICERS' CERTIFICATE. The Bank shall have received a
certificate of the officers of the Borrower setting forth (i) resolutions of its
board of directors in form and substance satisfactory to the Bank authorizing
the Borrower (and such other parties as may be required by Bank) to execute the
Loan Documents to which it is a party, and (ii) specimen signatures of the
officers so authorized.

         Section 4.3 ADDITIONAL DOCUMENTATION. The Borrower shall deliver to the
Bank such additional approvals, opinions or documents as Bank may reasonably
require.

                                       5
<PAGE>

                                    ARTICLE 5

                                  MISCELLANEOUS

         Section 5.1 LOAN DOCUMENTS. All Loan Documents shall secure the
indebtedness and obligations previously secured by such Loan Documents, as such
indebtedness and obligations are affected by this Fourth Amendment (including,
without limitation, the $500,000.00 Renewed and Extended Promissory Note of even
date herewith from the Borrower to the Bank), whether or not such Loan Documents
shall be expressly amended or supplemented in connection with this Fourth
Amendment.

         Section 5.2 EXTENT OF AMENDMENTS. Except as otherwise expressly
provided herein, the Agreement, the Loan Documents, the Line of Credit and the
other instruments and agreements referred to therein are not amended, modified
or affected by this Fourth Amendment.

         Section 5.3 EFFECTIVE DATE. Except as otherwise expressly provided
herein, the effective date of all provisions of this Fourth Amendment shall be
the date of execution indicated below.

         Section 5.4 TITLES OF ARTICLES, SECTIONS AND SUBSECTIONS. All titles or
headings to articles, sections, subsections or other divisions of this Fourth
Amendment are only for the convenience of the parties and shall not be construed
to have any effect or meaning with respect to the other content of such
articles, sections, subsections, or other divisions, such other content being
controlling as to the Agreement among the parties hereto.

         Section 5.5 COUNTERPARTS. This Fourth Amendment may be executed in two
or more counterparts. It will not be necessary that the signatures of all
parties hereto be contained on any one counterpart hereof; each counterpart
shall be deemed an original, but all of which together shall constitute one and
the same instrument.

         Section 5.6 FEES AND EXPENSES. Borrower will pay all fees and expenses
incurred by Bank in connection with this Agreement and the transactions
contemplated herein including, without limitation filing fees, search fees, and
reasonable attorneys' fees.

         Section 5.7 ENTIRE AGREEMENT. THIS FOURTH AMENDMENT AND ALL OTHER
INSTRUMENTS, DOCUMENTS, AND AGREEMENTS EXECUTED AND DELIVERED IN CONNECTION WITH
THIS FOURTH AMENDMENT EMBODY THE FINAL, ENTIRE AGREEMENT AMONG THE PARTIES
HERETO WITH RESPECT TO THE SUBJECT MATTER HEREOF AND THEREOF AND SUPERSEDE ANY
AND ALL PRIOR COMMITMENTS, AGREEMENTS, REPRESENTATIONS AND UNDERSTANDINGS,
WHETHER WRITTEN OR ORAL, RELATING TO THIS FOURTH AMENDMENT AND THE OTHER
INSTRUMENTS, DOCUMENTS AND AGREEMENTS EXECUTED AND DELIVERED IN CONNECTION WITH
THIS FOURTH AMENDMENT, AND MAY NOT BE CONTRADICTED OR VARIED BY EVIDENCE OF
PRIOR, CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS OR DISCUSSIONS OF THE
PARTIES HERETO. THERE ARE NO ORAL AGREEMENTS AMONG THE PARTIES HERETO.

                                       6
<PAGE>

         IN WITNESS WHEREOF, the parties hereto have caused this instrument to
be duly executed as of the 30th day of April, 2002.

                                              BORROWER:

                                              MOUNTAIN COMPRESSED AIR, INC.


                                              By:   /s/ THEODORE F. POUND, III
                                                    ----------------------------
                                                    Theodore F. Pound, III
                                                    Vice President and Secretary


                                              BANK:

                                              WELLS FARGO BANK TEXAS,
                                              NATIONAL ASSOCIATION


                                              By:   /s/ SCOTT GILDEA
                                                    ----------------------------
                                                    Scott Gildea
                                                    Assistant Vice President



The Parent hereby consents and agrees to this Fourth Amendment and agrees that
the OilQuip Guaranty shall remain in full force and effect, shall continue to
the be legal, valid, and binding obligations of the Parent, and shall continue
to guarantee the indebtedness and obligations described in the OilQuip Guaranty
as such guaranteed obligations are amended by this Fourth Amendment including,
without limitation, such OilQuip Guaranty shall cover the $500,000.00 Renewed
and Extended Line of Credit Note, together with any and all renewals,
extensions, rearrangements, amendments, modifications, and/or increases of any
of the aforesaid, and such OilQuip Guaranty shall be enforceable against OilQuip
in accordance with its terms.

                                       7
<PAGE>

                                              GUARANTOR:

                                              OilQuip Rentals, Inc.,
                                              a Delaware corporation


                                              By:  /s/ THEODORE F. POUND, III
                                                   -----------------------------
                                                   Theodore F. Pound, III
                                                   Vice President and Secretary


Munawar and Jayne Hidayatallah hereby jointly and severally consent and agree to
this Fourth Amendment and agree that the Hidayatallah Guaranty shall remain in
full force and effect, shall continue to the be legal, valid, and binding
obligations of Munawar and Jayne Hidayatallah, and shall continue to guaranty
the indebtedness and obligations described in the Hidayatallah Guaranty as such
guaranteed obligations are amended by this Fourth Amendment including, without
limitation, such Hidayatallah Guaranty shall cover the $500,000.00 Renewed and
Extended Line of Credit Note, together with any and all renewals, extensions,
rearrangements, amendments, modifications, and/or increases of any of the
aforesaid, and such Hidayatallah Guaranty shall be enforceable against Munawar
and Jayne Hidayatallah in accordance with its terms.

                                               GUARANTOR:



                                               /S/ MUNAWAR HIDAYATALLAH
                                               ---------------------------------
                                               Munawar Hidayatallah



                                               /s/ Jayne Hidayatallah
                                               ---------------------------------
                                               Jayne Hidayatallah

                                       8
<PAGE>

Allis-Chalmers consents and agrees to this Fourth Amendment and agrees to comply
with and be bound by all of the terms hereof, and further agrees that its
guaranty shall remain in full force and effect, shall continue to the be legal,
valid, and binding obligations of Allis-Chalmers, and shall continue to
guarantee the indebtedness and obligations described in its guaranty as such
guaranteed obligations are amended by this Fourth Amendment including, without
limitation, such guaranty shall cover the $500,000.00 Renewed and Extended Line
of Credit Note, together with any and all renewals, extensions, rearrangements,
amendments, modifications, and/or increases of any of the aforesaid, and such
guaranty shall be enforceable against Allis-Chalmers in accordance with its
terms.


                                              GUARANTOR:

                                              Allis-Chalmers Company,
                                              a Delaware corporation


                                              By:  /s/ MUNAWAR HIDAYATALLAH
                                                   -----------------------------
                                                   Munawar Hidayatallah
                                                   Chief Executive Officer


                                       9
<PAGE>

                                   EXHIBIT A-1


RENEWED AND EXTENDED REVOLVING LINE OF CREDIT NOTE


$500,000.00                                                     Houston, Texas
                                                                April 30, 2002

         FOR VALUE RECEIVED, the undersigned MOUNTAIN COMPRESSED AIR, INC., a
Texas corporation ("Borrower"), promises to pay to the order of WELLS FARGO BANK
TEXAS, NATIONAL ASSOCIATION ("Bank") at its office at 1000 Louisiana, 3rd Floor,
Houston, Texas, or at such other place as the holder hereof may designate, in
lawful money of the United States of America and in immediately available funds,
the principal sum of Five Hundred Thousand and No/100 Dollars ($500,000.00), or
so much thereof as may be advanced and be outstanding, with interest thereon, to
be computed on each advance from the date of its disbursement as set forth
herein.

INTEREST:

ARTICLE 6 INTEREST. The Borrower agrees to pay interest at the Bank's address
listed above on the unpaid principal note hereof and, to the extent permitted by
law, the accrued interest in respect hereof from time to time from the date
hereof until payment in full of the principal amount hereof and accrued interest
hereon, at the rates and on the dates set forth on the Addendum attached hereto
and incorporated herein for all purposes.

ARTICLE 7 PAYMENT OF INTEREST. Interest accrued on this Note shall be payable on
the last day of each April, July, October, and January of each year, commencing
on the first such day after the date of this Note and on maturity hereof.

ARTICLE 8 DEFAULT INTEREST. From and after the maturity date of this Note, or
such earlier date as all principal owing hereunder becomes due and payable by
acceleration or otherwise, the outstanding principal balance of this Note shall
bear interest until paid in full at an increased rate per annum (computed on the
basis of a 360-day year, actual days elapsed, unless such calculation would
result in a usurious rate, in which case interest shall be computed on the basis
of a 365/366-day year, as the case may be, actual days elapsed) equal to two
percent (2%) above the rate of interest from time to time applicable to this
Note, but in no event at a rate greater than the Maximum Rate.

BORROWING AND REPAYMENT:

ARTICLE 9 BORROWING AND REPAYMENT. Borrower may from time to time during the
term of this Note borrow, partially or wholly repay its outstanding borrowings,
and reborrow, subject to all of the limitations, terms and conditions of this
Note and of any document executed in connection with or governing this Note;
provided however, that the total outstanding borrowings under this Note shall
not at any time exceed the principal amount stated above. The unpaid principal
balance of this obligation at any time shall be the total amounts advanced
hereunder by the holder hereof less the amount of principal payments made hereon
by or for any Borrower, which balance may be endorsed hereon from time to time
by the holder. The outstanding principal balance of this Note shall be due and
payable in full on April 30, 2003.

                                       10
<PAGE>

ARTICLE 10 ADVANCES. Advances hereunder, to the total amount of the principal
sum stated above, may be made by the holder at the oral or written request of
(i) Linda Huskey, V. William Archer, III, or M.H. Hidayatallah, any one acting
alone, who are authorized to request advances and direct the disposition of any
advances until written notice of the revocation of such authority is received by
the holder at the office designated above, or (ii) any person, with respect to
advances deposited to the credit of any deposit account of any Borrower, which
advances, when so deposited, shall be conclusively presumed to have been made to
or for the benefit of each Borrower regardless of the fact that persons other
than those authorized to request advances may have authority to draw against
such account. The holder shall have no obligation to determine whether any
person requesting an advance is or has been authorized by any Borrower. The
amount and date of each advance requested hereunder shall be designated by an
authorized representative's execution of a Borrowing Request to be received by
the Bank at least one (1) Business Day prior to the date of such loan, which
date shall be a Business Day. Each advance requested hereunder shall be made at
the office of the Bank, and shall be funded prior to 2:00 p.m. Houston time on
the day so requested in immediately available funds in the amount so requested.

ARTICLE 11 APPLICATION OF PAYMENTS. Each payment made on this Note shall be
credited first, to any interest then due and second, to the outstanding
principal balance hereof.

EVENTS OF DEFAULT:

         The occurrence of any of the following shall constitute an "Event of
Default" under this Note:

         (a) The failure to pay any principal, interest, fees or other charges
when due hereunder or under any contract, instrument or document executed in
connection with this Note.

ARTICLE 12 The filing of a petition by or against any Borrower, any guarantor of
this Note or any general partner or joint venturer in any Borrower which is a
partnership or a joint venture (with each such guarantor, general partner and/or
joint venturer referred to herein as a "Third Party Obligor") under any
provisions of the Bankruptcy Reform Act, Title 11 of the United States Code, as
amended or recodified from time to time, or under any similar or other law
relating to bankruptcy, insolvency, reorganization or other relief for debtors;
the appointment of a receiver, trustee, custodian or liquidator of or for any
part of the assets or property of any Borrower or Third Party Obligor; any
Borrower or Third Party Obligor becomes insolvent, makes a general assignment
for the benefit of creditors or is generally not paying its debts as they become
due; or any attachment or like levy on any property of any Borrower or Third
Party Obligor.

ARTICLE 13 The death or incapacity of any individual Borrower or Third Party
Obligor, or the dissolution or liquidation of any Borrower or Third Party
Obligor which is a corporation, partnership, joint venture or other type of
entity.

ARTICLE 14 Any default in the payment or performance of any obligation, or any
defined event of default, under any provisions of any contract, instrument or
document pursuant to which any Borrower or Third Party Obligor has incurred any
obligation for borrowed money, any purchase obligation, or any other liability
of any kind to any person or entity, including the holder.

                                       11
<PAGE>

ARTICLE 15 Any financial statement provided by any Borrower or Third Party
Obligor to Bank proves to be incorrect, false or misleading in any material
respect.

ARTICLE 16 Any sale or transfer of all or a substantial or material part of the
assets of any Borrower or Third Party Obligor other than in the ordinary course
of its business.

ARTICLE 17 Any violation or breach of any provision of, or any defined event of
default under, any addendum to this Note or any other promissory note or any
credit agreement (including without limitation that certain Credit Agreement
dated as of even date herewith between Borrower and the Bank), guaranty,
security agreement, deed of trust, mortgage, pledge agreement, subordination
agreement, or other document executed in connection with or securing this Note.

MISCELLANEOUS:

         (b) REMEDIES. Upon the occurrence of any Event of Default, the holder
of this Note, at the holder's option, may declare all sums of principal and
accrued and unpaid interest outstanding hereunder to be immediately due and
payable without presentment, demand, or any notices of any kind, including
without limitation notice of nonperformance, notice of protest, protest, notice
of dishonor, notice of intention to accelerate or notice of acceleration, all of
which are expressly waived by each Borrower, and the obligation, if any, of the
holder to extend any further credit hereunder shall immediately cease and
terminate. Each Borrower shall pay to the holder immediately upon demand the
full amount of all payments, advances, charges, costs and expenses, including
reasonable attorneys' fees (to include outside counsel fees and all allocated
costs of the holder's in-house counsel to the extent permissible), expended or
incurred by the holder in connection with the enforcement of the holder's rights
and/or the collection of any amounts which become due to the holder under this
Note, and the prosecution or defense of any action in any way related to this
Note, including without limitation, any action for declaratory relief, whether
incurred at the trial or appellate level, in an arbitration proceeding or
otherwise, and including any of the foregoing incurred in connection with any
bankruptcy proceeding (including without limitation, any adversary proceeding,
contested matter or motion brought by Bank or any other person) relating to any
Borrower or any other person or entity.

ARTICLE 18 OBLIGATIONS JOINT AND SEVERAL. Should more than one person or entity
sign this Note as a Borrower, the obligations of each such Borrower shall be
joint and several.

ARTICLE 19 GOVERNING LAW. THIS NOTE SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF TEXAS. THIS NOTE IS PERFORMABLE IN
HARRIS COUNTY, TEXAS. ANY ACTION OR PROCEEDING UNDER OR IN CONNECTION WITH THIS
NOTE AGAINST THE BORROWER OR ANY THIRD PARTY OBLIGOR MAY BE BROUGHT IN ANY STATE
OR FEDERAL COURT IN HARRIS COUNTY, TEXAS. BORROWER AND EACH THIRD PARTY OBLIGOR
HEREBY IRREVOCABLY (I) SUBMITS TO THE NON-EXCLUSIVE JURISDICTION OF SUCH COURTS,
AND (II) WAIVES ANY OBJECTION IT MAY NOW OR HEREAFTER HAVE AS TO THE VENUE OF
ANY SUCH ACTION OR PROCEEDING BROUGHT IN SUCH COURT OR THAT SUCH COURT IS AN
INCONVENIENT FORUM. NOTHING HEREIN SHALL AFFECT THE RIGHT OF THE BANK TO BRING
ANY ACTION OR PROCEEDING AGAINST THE BORROWER OR ANY THIRD PARTY OBLIGOR OR WITH
RESPECT TO ANY COLLATERAL IN ANY STATE OR FEDERAL COURT IN ANY OTHER
JURISDICTION. ANY ACTION OR PROCEEDING BY THE BORROWER OR ANY THIRD PARTY
OBLIGOR AGAINST LENDER SHALL BE BROUGHT ONLY IN A COURT LOCATED IN HARRIS
COUNTY, TEXAS.

                                       12
<PAGE>

ARTICLE 20 SAVINGS CLAUSE. It is the intention of the parties to comply strictly
with applicable usury laws. Accordingly, notwithstanding any provision to the
contrary in this Note, or in any contract, instrument or document evidencing or
securing the payment hereof or otherwise relating hereto (each, a "Related
Document"), in no event shall this Note or any Related Document require the
payment or permit the payment, taking, reserving, receiving, collection or
charging of any sums constituting interest under applicable laws that exceed the
maximum amount permitted by such laws, as the same may be amended or modified
from time to time (the "Maximum Rate"). If any such excess interest is called
for, contracted for, charged, taken, reserved or received in connection with
this Note or any Related Document, or in any communication by Bank or any other
person to Borrower or any other person, or in the event that all or part of the
principal or interest hereof or thereof shall be prepaid or accelerated, so that
under any of such circumstances or under any other circumstance whatsoever the
amount of interest contracted for, charged, taken, reserved or received on the
amount of principal actually outstanding from time to time under this Note shall
exceed the Maximum Rate, then in such event it is agreed that: (i) the
provisions of this paragraph shall govern and control; (ii) neither Borrower nor
any other person or entity now or hereafter liable for the payment of this Note
or any Related Document shall be obligated to pay the amount of such interest to
the extent it is in excess of the Maximum Rate; (iii) any such excess interest
which is or has been received by Bank, notwithstanding this paragraph, shall be
credited against the then unpaid principal balance hereof or thereof, or if this
Note or any Related Document has been or would be paid in full by such credit,
refunded to Borrower; and (iv) the provisions of this Note and each Related
Document, and any other communication to Borrower, shall immediately be deemed
reformed and such excess interest reduced, without the necessity of executing
any other document, to the Maximum Rate. The right to accelerate the maturity of
this Note or any Related Document does not include the right to accelerate,
collect or charge unearned interest, but only such interest that has otherwise
accrued as of the date of acceleration. Without limiting the foregoing, all
calculations of the rate of interest contracted for, charged, taken, reserved or
received in connection with this Note and any Related Document which are made
for the purpose of determining whether such rate exceeds the Maximum Rate shall
be made to the extent permitted by applicable laws by amortizing, prorating,
allocating and spreading during the period of the full term of this Note or such
Related Document, including all prior and subsequent renewals and extensions
hereof or thereof, all interest at any time contracted for, charged, taken,
reserved or received by Bank. The terms of this paragraph shall be deemed to be
incorporated into each Related Document.

         To the extent that either Chapter 303 or 306, or both, of the Texas
Finance Code apply in determining the Maximum Rate, Bank hereby elects to
determine the applicable rate ceiling by using the weekly ceiling from time to
time in effect, subject to Bank's right subsequently to change such method in
accordance with applicable law, as the same may be amended or modified from time
to time.

                                       13
<PAGE>

ARTICLE 21 RIGHT OF SETOFF; DEPOSIT ACCOUNTS. Upon and after the occurrence of
an Event of Default, (i) Borrower hereby authorizes Bank, at any time and from
time to time, without notice, which is hereby expressly waived by Borrower, and
whether or not Bank shall have declared this Note to be due and payable in
accordance with the terms hereof, to set off against, and to appropriate and
apply to the payment of, Borrower's obligations and liabilities under this Note
(whether matured or unmatured, fixed or contingent, liquidated or unliquidated),
any and all amounts owing by Bank to Borrower (whether payable in U.S. dollars
or any other currency, whether matured or unmatured, and in the case of
deposits, whether general or special (except trust and escrow accounts), time or
demand and however evidenced), and (ii) pending any such action, to the extent
necessary, to hold such amounts as collateral to secure such obligations and
liabilities and to return as unpaid for insufficient funds any and all checks
and other items drawn against any deposits so held as Bank, in its sole
discretion, may elect. Borrower hereby grants to Bank a security interest in all
deposits and accounts maintained with Bank and with any other financial
institution to secure the payment of all obligations and liabilities of Borrower
to Bank under this Note.

ARTICLE 22 CERTAIN TRI-PARTY ACCOUNTS. Borrower and Bank agree that Chapter 346
of the Texas Finance Code (which regulates certain revolving credit accounts and
revolving triparty accounts) shall not apply to any revolving loan accounts
created under this Note or maintained in connection herewith.

ARTICLE 23 This note is in renewal, extension and reduction of, but not in
novation or discharge of, that certain Revolving Line of Credit Note dated as of
January 31, 2002, in the original principal amount of $775,000.00, executed by
the Borrower and payable to the order of the Bank.

NOTICE: THIS NOTE AND ALL OTHER DOCUMENTS RELATING TO THE INDEBTEDNESS EVIDENCED
HEREBY CONSTITUTE A WRITTEN LOAN AGREEMENT WHICH REPRESENTS 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 RELATING TO THIS NOTE AND THE
INDEBTEDNESS EVIDENCED HEREBY.

         IN WITNESS WHEREOF, the undersigned has executed this Note as of the
date first written above.

                                                MOUNTAIN COMPRESSED AIR, INC.

                                                By: /S/THEODORE F. POUND, III
                                                    ----------------------------
                                                    Theodore F. Pound, III
                                                    Vice President & Secretary

                                       14
<PAGE>

ADDENDUM TO RENEWED AND EXTENDED REVOLVING LINE OF CREDIT NOTE
(BASE RATE PRICING ADJUSTMENTS)


         THIS ADDENDUM is attached to and made a part of that certain renewed
and extended promissory note executed by MOUNTAIN COMPRESSED AIR, INC., a Texas
corporation ("Borrower") and payable to WELLS FARGO BANK TEXAS, NATIONAL
ASSOCIATION ("Bank"), or order, dated as of April 30, 2002 in the principal
amount of FIVE HUNDRED THOUSAND AND NO/DOLLARS ($500,000.00) (the "Note").

         The following provisions are hereby incorporated into the Note to
reflect the interest rate adjustments agreed to by Bank and Borrower:

ARTICLE 24 DEFINITIONS

         As used herein, the following terms shall have the meanings set forth
after each, and any other term defined herein:

         Section 24.1 "BASE RATE" shall mean the higher of (a) Prime Rate per
annum in effect on that day, and (b) the Federal Fund Rate in effect on that day
as announced by the Federal Reserve Bank of New York, plus 0.5% per annum.

         Section 24.2 BUSINESS DAY" shall mean any day except a Saturday,
Sunday, or any other day on which commercial banks in Texas are authorized or
required to close by law.

         Section 24.3 "PRIME RATE" shall mean at any time the rate of interest
most recently announced within the Bank at its principal office in San Francisco
at its Prime Rate, with the understanding that the Bank's Prime Rate is one of
its base rates and serves as the basis upon which effective rates of interest
are calculated for those loans making reference thereto; and is evidenced by the
recording thereof after its announcement in such internal publication or
publications as the Bank may designate.

ARTICLE 25 INTEREST RATE ADJUSTMENTS

         Section 25.1 INITIAL INTEREST RATES. The initial interest rates
applicable to this Note shall be the rates set forth in the "INTEREST" paragraph
herein.

         Section 25.2 INTEREST RATE ADJUSTMENTS. In addition to any interest
rate adjustments resulting from changes in the Base Rate, Bank shall adjust the
Base Rate margin used to determine the rates of interest applicable to the Note
on the last day of each April, July, October, and January (each a "Quarterly
Date") of each year, commencing on the first Quarterly Date after the date of
the Note, if required to reflect a change in Borrower's ratio of Total Funded
Debt to EBITDA (as such terms are defined in the Credit Agreement referenced
herein), in accordance with the following grid:

                                       15
<PAGE>

                                                BASE                 UNUSED
         TOTAL FUNDED                           RATE                 COMMITMENT
         DEBT TO EBITDA                         MARGIN               FEE
         --------------                         ------               ---
         greater than 2.0 to 1.0                0.5%                 0.5%

         at least 2.0 to 1.0 but
         less than 2.5 to 1.0                    .75%                0.5%

         at least 2.5 to 1.0 but
         less than 3.0 to 1.0                   1.0%                 0.5%

         less than 3.0 to 1.0                   1.25%                0.5%


Each such adjustment shall be effective on the first Business Day of the
calendar quarter following the quarter during which Bank receives and reviews
Borrower's most current calendar quarter-end financial statements in accordance
with any requirements established by Bank for the preparation and delivery
thereof.

         IN WITNESS WHEREOF, this Addendum has been executed as of the same date
as the Note.

                                               MOUNTAIN COMPRESSED AIR, INC.



                                               By: /S/ THEODORE F. POUND, III
                                                   -----------------------------
                                                    Theodore F. Pound, III
                                                    Vice President & Secretary




                                       16