<PAGE>

                                                                   EXHIBIT 10.46

                      SECOND AMENDMENT TO CREDIT AGREEMENT

         THIS SECOND AMENDMENT TO CREDIT AGREEMENT (as same may be renewed,
extended, modified, restated amended and/or rearranged, the "Second Amendment")
dated as of April 2, 2004, is between AIRCOMP L.L.C., a Delaware limited
liability company (hereinafter referred to as "Borrower") and WELLS FARGO BANK,
NATIONAL ASSOCIATION, successor-by-merger to 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 June 27, 2003 (the "Original Agreement"); as amended by that certain First
Amendment to Credit Agreement dated as of December 31, 2003 (the "First
Amendment", together with the Original Agreement, referred to herein as the
"Agreement").

         B. Borrower has requested that Bank amend certain covenants set forth
in the Agreement. Bank has agreed to do so, subject to the terms and conditions
contained herein.

         C. Mountain Compressed Air, Inc., a Texas corporation ("MCA"), M-I
L.L.C., a Delaware limited liability company ("M-I"), and Munawar and Jayne
Hidayatallah (the "Hidayatallahs") 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 Second 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 Second
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.

         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 Second Amendment. It is hereby confirmed
that the term "Agreement" includes the Agreement as amended by this Second
Amendment.

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                                    ARTICLE 2

                                   AMENDMENTS

         Section 2.1 AMENDMENT TO SECTION 5.9. Effective as of the date hereof,
Section 5.9 of the Agreement is hereby amended to read in its entirety as
follows:

                  "SECTION 5.9 LIMITATIONS ON LEASES. Create, incur, assume or
         permit to exist any obligation for the payment of rent or hire or
         property of any kind whatsoever under leases or lease agreements
         including, without limitation, operating leases which will cause the
         aggregate amount of all payments made by Borrower pursuant to all such
         leases or lease agreements to exceed $200,000.00 in any fiscal year."

                                    ARTICLE 3

                         REPRESENTATIONS AND WARRANTIES

         In order to induce the Bank to enter into this Second 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:

         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 Second 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 Second Amendment.

         Section 3.3 DEFAULTS. There exists, and after giving effect to this
Second 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 Second
Amendment is intended to amend any of the representations or warranties of the
Agreement.


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                                    ARTICLE 4

                                   CONDITIONS

         The Bank has relied upon the representations and warranties contained
in this Second 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 Second Amendment
and to the following further conditions:

         Section 4.1 CERTIFICATE AND AGREEMENT OF MANAGERS - BORROWER. The Bank
shall have received a certificate and agreement of managers of the Borrower
setting forth (i) resolutions of its managers 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 managers so authorized.

         Section 4.2 ADDITIONAL DOCUMENTATION. The Borrower shall deliver to the
Bank such additional approvals, opinions or documents as Bank may reasonably
require.

                                    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 Second Amendment (including,
without limitation, the $1,000,000.00 Renewed Line of Credit Note, the
$8,000,000.00 Term Note, and the $1,000,000.00 Delayed Draw Term Note, each
dated as of June 27, 2003 from the Borrower to the Bank), whether or not such
Loan Documents shall be expressly amended or supplemented in connection with
this Second Amendment.

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

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

         Section 5.4 TITLES OF ARTICLES, SECTIONS AND SUBSECTIONS. All titles or
headings to articles, sections, subsections or other divisions of this Second
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 Second 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.

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

         Section 5.7 ENTIRE AGREEMENT. THIS SECOND AMENDMENT AND ALL OTHER
INSTRUMENTS, DOCUMENTS, AND AGREEMENTS EXECUTED AND DELIVERED IN CONNECTION WITH
THIS SECOND 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 SECOND AMENDMENT AND THE OTHER
INSTRUMENTS, DOCUMENTS AND AGREEMENTS EXECUTED AND DELIVERED IN CONNECTION WITH
THIS SECOND 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.

         IN WITNESS WHEREOF, the parties hereto have caused this instrument to
be effective as of the 2nd day of April, 2004.

                                                     BORROWER:

                                                     AIRCOMP L.L.C.


                                                     By:   /S/ TERRY KEANE
                                                           ---------------------
                                                           Terry Keane
                                                           President


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                                                     BANK:

                                                     WELLS FARGO BANK,
                                                     NATIONAL ASSOCIATION,
                                                     SUCCESSOR-BY-MERGER TO
                                                     WELLS FARGO BANK TEXAS,
                                                     NATIONAL ASSOCIATION


                                                     By:   /S/ ALAN SMITH
                                                           ---------------------
                                                           Alan Smith
                                                           Vice President


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MCA hereby consents and agrees to this Second Amendment and agrees that its (i)
guaranty executed on June 27, 2003 ("MCA Guaranty") and (ii) Third Party Pledge
executed on June 27, 2003 ("MCA Pledge") shall each remain in full force and
effect, shall continue to be legal, valid, and binding obligations of MCA, and
shall continue to guarantee and secure the indebtedness and obligations
described in the MCA Guaranty and the MCA Pledge as such guaranteed and secured
obligations are amended by this Second Amendment including, without limitation,
the MCA Guaranty shall cover the $1,000,000.00 Line of Credit Note, the
$8,000,000.00 Term Note, and the $1,000,000.00 Delayed Draw Term Note, together
with any and all renewals, rearrangements, amendments, increases, extensions
and/or modifications of any of the aforesaid, and the MCA Guaranty and the MCA
Pledge shall each be enforceable against MCA in accordance with their terms.

                                          GUARANTOR:

                                          Mountain Compressed Air, Inc.,
                                          a Texas corporation


                                          By:      /S/ TED POUND
                                                   -----------------------------
                                                   Theodore F. Pound, III
                                                   Vice President and Secretary


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Munawar and Jayne Hidayatallah hereby jointly and severally consent and agree to
this Second Amendment and agree that the Hidayatallah Guaranty executed June 27,
2003 shall remain in full force and effect, shall continue to 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 Second Amendment including,
without limitation, such Hidayatallah Guaranty shall cover the $1,000,000.00
Line of Credit Note, the $8,000,000.00 Term Note, and the $1,000,000.00 Delayed
Draw Term Note, together with any and all renewals, rearrangements, amendments,
increases, extensions and/or modifications 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 H. HIDAYATALLAH
                                                     ---------------------------
                                                     Munawar Hidayatallah




                                                     JAYNE HIDAYATALLAH
                                                     ---------------------------
                                                     Jayne Hidayatallah


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M-I consents and agrees to this Second Amendment and agrees that its (i)
guaranty executed on June 27, 2003 ("M-I Guaranty") and (ii) Third Party Pledge
executed on June 27, 2003 ("M-I Pledge") shall each remain in full force and
effect, shall continue to be legal, valid, and binding obligations of M-I, and
shall continue to guarantee and secure the indebtedness and obligations
described in the M-I Guaranty and the M-I Pledge as such guaranteed and secured
obligations are amended by this Second Amendment including, without limitation,
the M-I Guaranty shall cover the $1,000,000.00 Line of Credit Note, the
$8,000,000.00 Term Note, and the $1,000,000.00 Delayed Draw Term Note, together
with any and all renewals, rearrangements, amendments, and/or modifications of
any of the aforesaid, and such M-I Guaranty and the M-I Pledge shall each be
enforceable against M-I in accordance with their terms.

                                     GUARANTOR:

                                     M-I L.L.C.,
                                     a Delaware limited liability company


                                     By:    /S/ CHRIS RIVERS
                                            ------------------------------------
                                            Chris Rivers
                                            Senior Vice President, Chief
                                             Financial Officer and Treasurer


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