Document:

<PAGE>
                                                                  EXHIBIT 10.15

                        AGREEMENT AND SECOND AMENDMENT TO
                                CREDIT AGREEMENT

         This Agreement and Second Amendment to Credit Agreement (this
"Amendment") dated as of August 12, 2002 among the financial institutions
(collectively, the "Lenders") party to the Credit Agreement (as such term is
hereinafter defined); AMERICAN PLUMBING & MECHANICAL, INC. (the "Borrower"), and
BANK ONE, NA (successor by merger to The First National Bank of Chicago), as
agent (in such capacity, the "Agent") for the Lenders;

                                   WITNESSETH:

         WHEREAS, the Borrower, the Lenders, the Agent and the Documentation
Agent executed and delivered that certain Credit Agreement (as heretofore
amended and supplemented, the "Credit Agreement") dated as of March 31, 2001;
and

         WHEREAS, the Borrower, the Lenders and the Agent now desire to amend
the Credit Agreement further to (a) reduce the Commitment of each Lender; (b)
require evidence of compliance with Section 6.26 of the Credit Agreement before
any payment of principal or interest on the Permitted Senior Subordinated Debt;
(c) prohibit the Borrower from paying any dividends on any of its Capital Stock;
(d) change the interest rate to accrue on the Loans; (e) prohibit the Borrower
from making acquisitions or prepaying any Indebtedness other than the Loans; (f)
require the Borrower to provide its monthly financial statements; (g) change
certain financial covenants, and add a new financial covenant; (h) limit Capital
Expenditures; (i) permit certain asset sales, and (j) otherwise amend the Credit
Agreement;

         NOW, THEREFORE, in consideration of the premises and the mutual
agreements, representations and warranties herein set forth, and for other good
and valuable consideration, the receipt and sufficiency of which are
acknowledged, the parties here do hereby agree as follows:

         Section 1. Each of the following definitions contained in Section 1.1
of the Credit Agreement is hereby amended to read in its entirety as follows:

                  "Commitment" means, for each Lender, the obligation of such
         Lender to make Loans to, and participate in Facility LCs issued upon
         the application of, the Borrower in an aggregate amount not exceeding
         the amount set forth opposite its name on Appendix A hereto (and such
         Commitment shall reduce as shown on Appendix A as of the date shown for
         each such reduction) or as set forth in any Assignment Agreement
         relating to any assignment that has become effective pursuant to
         Section 12.03.02 (with such Commitment to reduce proportionately on
         each date when the assignor's Commitment was to be reduced as shown on
         Appendix A), as such amount may be reduced from time to time by such
         Lender's Pro Rata Share of each principal payment made on the Loans
         pursuant to clause (i) of Section 2.02, as such amount may be further
         modified from time to time pursuant to the terms hereof.

                  "Consolidated Cash Taxes" means, with reference to any period,
         the aggregate pro forma amount of income Taxes of the Borrower and its
         Subsidiaries

<PAGE>

         calculated on a consolidated basis for such period at an assumed tax
         rate of thirty-nine percent (39%) of the sum of Consolidated Net Income
         plus provisions for taxes based on income or revenues, in each case for
         such period; provided that if from time to time the actual tax rate is
         significantly different from such assumed tax rate, then either the
         Agent (at the direction of the Required Lenders) or the Borrower may
         request a redetermination of the assumed tax rate and the redetermined
         tax rate (or, if applicable, rates) shall become the assumed tax rate
         for calculation purposes upon such redetermination until any future
         redetermination.

                  "Consolidated EBITDA" means, with reference to any period, on
         a trailing four fiscal quarter basis (using the historical financial
         results of any other business acquired in an Acquisition, to the extent
         applicable, without duplication, on a pro forma basis, consistent with
         SEC regulations), the sum of Consolidated Net Income plus, to the
         extent deducted in determining Consolidated Net Income, (i)
         Consolidated Interest Expense, (ii) provisions for taxes based on
         income or revenues, (iii) depreciation, (iv) amortization, (v) other
         non-cash expenses, (vi) losses from discontinued operations described
         on Appendix B hereto (provided, however, that the aggregate amount of
         such losses added pursuant to this clause (vi) shall not exceed
         $16,000,000), determined on a pre-tax basis, and (vii) on a pre-tax
         basis, any extraordinary or non-recurring losses (other than losses
         from discontinued operations) minus, to the extent included in
         determining Consolidated Net Income, any extraordinary or non-recurring
         gains, all calculated on a consolidated basis for the Borrower and its
         Subsidiaries and as determined in accordance with GAAP.

         Section 2. Section 6.01(ii) of the Credit Agreement is hereby amended
to read in its entirety as follows:

                  (ii) Within thirty-five (35) days after the close of the first
         three quarterly periods of each of its fiscal years, for itself and its
         Subsidiaries, consolidated and consolidating unaudited balance sheets
         as at the close of each such period and consolidated and consolidating
         profit and loss and reconciliation of surplus statements and a
         statement of cash flows for the period from the beginning of such
         fiscal year to the end of such quarter, together with a reconciliation
         of the calculation of Consolidated EBITDA with respect to losses from
         discontinued operations, all certified by its chief financial officer
         (consolidating statements need not cover cash flow reporting).

         Section 3. Section 6.01(ix) of the Credit Agreement is hereby
redesignated as Section 6.01(x) and there is hereby added to Section 6.01 of the
Credit Agreement a new Section 6.01(ix), which shall read in its entirety as
follows:

                  (ix) Within twenty (20) days after the end of each of the
         first two months of each quarter in each fiscal year, for itself and
         its Subsidiaries, (a) consolidated and consolidating unaudited balance
         sheets as at the close of each such period and (b) consolidated and
         consolidating profit and loss and reconciliation of surplus

                                      -2-
<PAGE>

         statements and a statement of cash flows for the period from the
         beginning of such fiscal year to the end of such month, all certified
         by its chief financial officer (consolidating statements need not cover
         cash flow reporting).

         Section 4. Section 6.09 of the Credit Agreement is hereby amended to
add thereto the following:

         Not in limitation of the foregoing, the Agent shall have the right
         without hindrance or delay to conduct field examinations to inspect or
         appraise the Property subject to the Collateral Documents and to
         inspect, audit and copy the books, records, journals, correspondence
         and other records and data of the Borrower and the Subsidiaries
         relating thereto or to their business. If the Agent prepares a formal
         written report in connection with any such examination (and the Agent
         is under no obligation to do so), it shall provide a copy of the same
         to each Lender; provided, however, that the preparation and delivery of
         any such report to the Lenders shall not constitute a representation or
         warranty of any type with respect thereto, including but not limited to
         a representation or warranty as to its accuracy or completeness. The
         Agent is authorized to discuss the affairs of the Borrower and the
         Subsidiaries with any Person, including without limitation the
         employees of the Borrower and the Subsidiaries, as the Agent may deem
         necessary in relation to the Property subject to the Collateral
         Documents, the financial condition of the Borrower and the Subsidiaries
         or the rights of the Agent and/or the Lenders under the Loan Documents.
         The Borrower agrees to pay the Agent's customary fees and disbursements
         relating to such field examinations. The Agent shall have full access
         to all records available to the Borrower from any credit reporting
         service, bureau or similar service, and shall have the right to examine
         and make copies of any such records. The Agent may exhibit a copy of
         this Agreement to such service and such service shall be entitled to
         rely on the provisions hereof in providing access to the Agent as
         provided herein.

         Section 5. Section 6.10 of the Credit Agreement is hereby amended to
read in its entirety as follows:

                  6.10. Dividends. The Borrower will not, nor will it permit any
         Subsidiary to, declare or pay any dividends or make any Distribution on
         its Capital Stock (other than dividends payable in its own Capital
         Stock) or redeem, repurchase or otherwise acquire or retire any of its
         Capital Stock at any time outstanding, except that any Subsidiary of
         the Borrower may declare and pay dividends and make Distributions (i)
         to a Wholly-Owned Subsidiary of the Borrower that is a Guarantor if no
         Default or Unmatured Default would result from such declaration,
         payment or making, or (ii) to the Borrower.

         Section 6. Section 6.12 of the Credit Agreement is hereby amended to
read in its entirety as follows:

                  6.12. Merger . The Borrower will not, nor will it permit any
         Subsidiary to, merge or consolidate with or into any other Person, or
         sell, convey, transfer,

                                      -3-
<PAGE>

         lease or otherwise dispose of (whether in one transaction or in a
         series of transactions) all or substantially all of its assets (whether
         now owned or hereafter acquired), except that a Subsidiary may merge
         into the Borrower or a Wholly-Owned Subsidiary.

         Section 7. Section 6.13 of the Credit Agreement is hereby amended to
add thereto a new Section 6.13(vi), which shall read in its entirety as follows:

                  (vi) Other sales or other dispositions of Property; provided,
         however, that in connection with each such sale or other disposition
         (a) the aggregate Commitment of the Lenders shall be reduced by 75% of
         the net cash proceeds thereof, as and when received, with the
         Commitment of each Lender then in effect to be reduced on a pro rata
         basis and each Commitment of each Lender set forth on Appendix A for
         each subsequent period to be reduced by the same amount, and (b) a
         prepayment on the Loans in the amount of 75% of the net cash proceeds
         thereof shall be due and payable as and when such cash proceeds are
         received.

         Section 8. Section 6.14 of the Credit Agreement is hereby amended to
read in its entirety as follows:

                  6.14. Investments and Acquisitions. The Borrower will not, nor
         will it permit any Subsidiary to, make or suffer to exist any
         Investments (including without limitation, loans and advances to, and
         other Investments in, Subsidiaries), or commitments therefor, or to
         create any Subsidiary or to become or remain a partner in any
         partnership or joint venture, or to make any Acquisition of any Person,
         except (i) Cash Equivalent Investments and (ii) Investments in
         Subsidiaries in existence on August 6, 2002 and described in Schedule
         III.

         Section 9. Section 6.20 of the Credit Agreement is hereby amended to
read in its entirety as follows:

                  6.20. Permitted Senior Subordinated Debt . The Borrower will
         not, and will not permit any Subsidiary to, (i) make any amendment or
         modification to the indenture, note or other agreement evidencing or
         governing any Permitted Senior Subordinated Debt, or directly or
         indirectly voluntarily prepay, defease or in substance defease,
         purchase, redeem, retire or otherwise acquire, any Permitted Senior
         Subordinated Debt, except any amendment or modification allowed under
         Section 6.19, or (ii) pay any interest accruing on any Permitted Senior
         Subordinated Debt unless (a) the Borrower provides the Agent with
         evidence that the Borrower was in compliance with Section 6.26 as of
         the last day of the most recent fiscal quarter to end before the
         proposed date of such payment, at least five (5) Business Days before
         the date such payment is made and (b) no Default or Unmatured Default
         then exists or would result from the payment of such interest.

         Section 10. Section 6.26.01 of the Credit Agreement is hereby amended
to read in its entirety as follows:

                                      -4-
<PAGE>

                  6.26.01. Total Debt to EBITDA Ratio. The Borrower will not
         permit the ratio, determined as of the end of each of its fiscal
         quarters for the then most-recently ended four fiscal quarters, of (i)
         Consolidated Funded Total Debt to (ii) Consolidated EBITDA to be
         greater than (a) 5.50 to 1 through December 31, 2002; (b) 5.00 to 1 as
         of March 31, 2003; (c) 4.75 to 1 as of June 30, 2003, and (d) 4.50 to 1
         thereafter.

         Section 11. Section 6.26.02 of the Credit Agreement is hereby amended
to read in its entirety as follows:

                  6.26.02. Senior Debt to EBITDA Ratio. The Borrower will not
         permit the ratio, determined as of the end of each of its fiscal
         quarters for the then most-recently ended four fiscal quarters, of (i)
         Consolidated Senior Total Debt to (ii) Consolidated EBITDA to be
         greater than (a) 2.65 to 1 as of September 30, 2002; (b) 2.50 to 1 as
         of December 31, 2002; (c) 2.40 to 1 as of March 31 and June 30, 2003,
         and (d) 2.25 to 1 thereafter.

         Section 12. Section 6.26.03 of the Credit Agreement is hereby amended
to read in its entirety as follows:

                  6.26.03. Fixed Charge Coverage Ratio. The Borrower will not
         permit the ratio, determined as of the end of each calendar month, of
         (i) Consolidated EBITDA minus the sum of Consolidated Cash Taxes and
         Consolidated Capital Expenditures, in each case for the 12 months then
         ending, to (ii) Consolidated Cash Interest Expense for the 12 months
         then ending, plus current maturities of principal Indebtedness as of
         the end of such month, plus one seventh (1/7th) of the Aggregate
         Outstanding Credit Exposure as of the end of such month, all calculated
         for the Borrower and its Subsidiaries on a consolidated basis, to be
         less than (a) .80 to 1 as of September 30, 2002; (b) .85 to 1 as of
         December 31, 2002, (c) .90 to 1 as of March 31 and June 30, 2003 and
         (d) .95 to 1 thereafter.

         Section 13. There is hereby added to the Credit Agreement a new Section
6.26.05, which shall read in its entirety as follows:

                  6.26.05 Cumulative EBITDA. The Borrower will have Consolidated
         EBITDA from July 1, 2002 (in the case of dates below in 2002) or
         January 1, 2003 (in the case of dates below in 2003) to each date
         indicated below of at least the corresponding amount set forth below:

<Table>
<Caption>
               Date                                         Minimum Cumulative EBITDA
               ----                                         -------------------------
<S>                                                         <C>
         September 30, 2002                                      $     8,500,000
         December 31, 2002                                       $    15,721,000
         March 31, 2003                                          $     6,425,000
         June 30, 2003                                           $    15,260,000
         September 30, 2003                                      $    24,400,000
         December 31, 2003                                       $    31,000,000
</Table>

                                       -5-
<PAGE>

         Section 14. Section 6.27 of the Credit Agreement is hereby amended to
read in its entirety as follows, effective for the fiscal quarter ending
September 30, 2002:

                  6.27. Capital Expenditures . The Borrower will not, nor will
         it permit any Subsidiary to, pay or incur Consolidated Capital
         Expenditures for any fiscal quarter in excess of $1,000,000.

         Section 15. There is hereby added to the Credit Agreement a new Section
6.28, which shall read in its entirety as follows:

                  6.28. Prepayments. The Borrower will not, nor will it permit
         any Subsidiary to, prepay any principal of any Indebtedness (other than
         the Loans); provided, however, that AMPAM Commercial Midwest, Inc. may
         prepay that certain promissory note made by it, dated March 11, 1997,
         payable to the order of The Central Ohio Transit District on or before
         March 3, 2003 and with an outstanding principal balance as of August 6,
         2001 of $75,000.00.

         Section 16. Attachments. Schedules I and III to the Credit Agreement
are hereby deleted and there are hereby substituted therefore new Schedules I
and III, which shall be identical to Schedules I and III, respectively, attached
hereto. The changes reflected in the revised Pricing Schedule shall be effective
as of the date hereof with respect to all then-outstanding Advances and Facility
LCs. The Credit Agreement is hereby amended to append thereto Appendices A and
B, which shall be identical to Appendices A and B, respectively, attached
hereto.

         Section 17. Projections. The Borrower has furnished the Lenders with
certain projections of the financial results of the Borrower as set forth on
Appendix C hereto. The Borrower represents and warrants that these projections
are the Borrower's best current projection of the results of operations of the
Borrower and the Subsidiaries for the period indicated therein; however, this
representation is not a representation that the actual result of such operations
will meet such projections.

         Section 18. Waiver. The Borrower has informed the Agent that, as of
June 30, 2002, the Borrower will not be in compliance with Sections 6.26.01 and
6.26.03 of the Credit Agreement as such provisions were in effect before giving
effect to this Amendment. The Required Lenders hereby waive compliance with
Sections 6.26.01 and 6.26.03 of the Credit Agreement as of June 30, 2002;
provided, however, that such waiver is conditioned upon compliance with Sections
6.26.01 and 6.26.03 of the Credit Agreement as of June 30, 2002 as such Sections
would have been in effect if this Amendment had been effective as of June 30,
2002.

         Section 19. Engagement of Advisors. The Borrower understands that the
Agent may engage, or cause its counsel to engage, one or more financial advisors
to advise the Lenders with respect to the financial condition, business and
prospects of the Borrower and the Subsidiaries and any proposed restructuring of
the capitalization of the Borrower and the Subsidiaries, including the terms
thereof. If any such advisor delivers a formal written report to the Agent in
connection with such engagement and does not furnish a copy thereof to each
Lender, the Agent shall furnish a copy thereof to each Lender; provided,
however, that such delivery shall not constitute a representation or warranty of
any type by the Agent with respect thereto. The

                                      -6-
<PAGE>

Borrower agrees that (i) it is responsible for the reasonable fees and
disbursements of any such advisor pursuant to Section 9.05 of the Credit
Agreement; (ii) it will cooperate fully with any such advisor in accordance with
Section 6.09 of the Credit Agreement, and (iii) neither it nor any Subsidiary
has no right to any work product of any such advisor.

         Section 20. Release. THE BORROWER, FOR ITSELF AND ON BEHALF OF EACH
SUBSIDIARY, ACKNOWLEDGES THAT ON THE DATE HEREOF ALL OBLIGATIONS OF THE BORROWER
TO THE AGENT, THE DOCUMENTATION AGENT, THE LC ISSUER AND THE LENDERS ARE PAYABLE
WITHOUT DEFENSE, OFFSET, COUNTERCLAIM OR RECOUPMENT. IN ADDITION, THE BORROWER,
FOR ITSELF AND ON BEHALF OF EACH SUBSIDIARY, HEREBY RELEASES ANY AND ALL CLAIMS,
CAUSES OF ACTION OR OTHER DISPUTES IT MAY HAVE AGAINST THE AGENT, THE
DOCUMENTATION AGENT, THE LC ISSUER, EACH LENDER, THEIR RESPECTIVE COUNSEL OR ANY
OF THEIR RESPECTIVE AGENTS, DIRECTORS, OFFICERS, EMPLOYEES, REPRESENTATIVES,
SUCCESSORS OR ASSIGNS OF ANY KIND OR NATURE ARISING OUT OF, RELATED TO, OR IN
ANY WAY CONNECTED WITH, THE LOAN DOCUMENTS, IN EACH CASE WHICH MAY HAVE ARISEN
ON OR BEFORE THE DATE OF THIS AMENDMENT AND REGARDLESS OF WHETHER THE SAME AROSE
OUT OF THE NEGLIGENCE OF THE PERSON BEING RELEASED OR OTHERWISE, EXCEPT AND TO
THE EXTENT THAT THE SAME AROSE OUT OF THE GROSS NEGLIGENCE OR WILLFUL MISCONDUCT
OF THE PERSON OTHERWISE BEING RELEASED. THE BORROWER HEREBY ACKNOWLEDGES THAT IT
HAS READ THIS AMENDMENT AND HAS CONFERRED WITH ITS COUNSEL AND ADVISORS
REGARDING ITS CONTENT, INCLUDING THIS SECTION, AND HEREBY AGREES TO WAIVE ANY
CLAIM THAT THE TERMS OF THIS AMENDMENT (INCLUDING, WITHOUT LIMITATION, THE
RELEASES CONTAINED HEREIN) AND THE LOAN DOCUMENTS (AS AMENDED HEREBY) ARE
INVALID OR OTHERWISE UNENFORCEABLE.

         Section 21. Conditions. This Amendment shall not become effective until
(i) it has been executed and delivered by the Borrower, each Guarantor and the
Required Lenders, (ii) the Borrower shall have delivered to the Agent a
certificate of the Secretary or any Assistant Secretary of the Borrower
authorizing the execution, delivery and performance of this Amendment and (iii)
the Borrower shall have paid to the Agent (for payment to the applicable
Lenders) a fee equal to 0.40% times the Commitment (as of the date of the
effectiveness of this Amendment, after giving effect to this Amendment) of each
Lender which shall have joined in the execution of this Amendment by the later
of (a) August 12, 2002 and (b) the date it has been executed by the Required
Lenders.

         Section 22. Representations True; No Default. The Borrower represents
and warrants that the representations and warranties contained in the Loan
Documents are true and correct in all material respects on and as of the date
hereof as though made on and as of such date. The Borrower hereby certifies that
no event has occurred and is continuing which constitutes an Unmatured Default
or a Default.

         Section 23. Ratification. Except as expressly amended hereby, the Loan
Documents shall remain in full force and effect. The Credit Agreement, as hereby
amended, and all rights

                                      -7-
<PAGE>

and powers created thereby or thereunder and under the other Loan Documents are
in all respects ratified and confirmed and remain in full force and effect.

         Section 24. Definitions and References. Any term used herein which is
defined in the Credit Agreement shall have the meaning therein ascribed to it.
The terms "Agreement" and "Credit Agreement" as used in the Loan Documents or
any other instrument, document or writing furnished to the Agent or any Lender
by any Obligor and referring to the Credit Agreement, shall mean the Credit
Agreement as hereby amended.

         Section 25. Miscellaneous. This Amendment (a) shall be binding upon and
inure to the benefit of the Borrower, the Lenders, the Agent, the Documentation
Agent and their respective successors, assigns, receivers and trustees (but the
Borrower shall not assign its rights hereunder without the express prior written
consent of the Required Lenders); (b) may be modified or amended only by a
writing signed by the party against whom the same is to be enforced; (c) may be
executed in several counterparts, and by the parties hereto on separate
counterparts, and each counterpart, when so executed and delivered, shall
constitute an original agreement, and all such separate counterparts shall
constitute but one and the same agreement; and (e) together with the other Loan
Documents, embodies the entire agreement and understanding between the parties
with respect to the subject matter hereof and supersedes all prior agreements,
consents and understandings relating to such subject matter.

                                      -8-
<PAGE>

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
signed by their respective duly authorized officers, effective as of the date
first above written.

         THE LOAN DOCUMENTS (INCLUDING THIS AMENDMENT) REPRESENT THE FINAL
AGREEMENT AMONG 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 AMONG THE PARTIES.

                                            AMERICAN PLUMBING & MECHANICAL,
                                            INC.

                                            By:
                                                -------------------------------
                                                   Steve Smith
                                                   Treasurer

                                      -9-
<PAGE>

                                           BANK ONE, NA (successor by merger to
                                           The First National Bank of Chicago),
                                           individually and as Agent

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

                                      -10-
<PAGE>

                                        CREDIT LYONNAIS NEW YORK BRANCH,
                                        individually and as Documentation Agent

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

                                      -11-
<PAGE>

                                           UNION BANK OF CALIFORNIA, N.A.

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

                                      -12-
<PAGE>

                                           FLEET NATIONAL BANK

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

                                      -13-
<PAGE>

                                           COMERICA BANK

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

                                      -14-
<PAGE>

                                           BAY VIEW FINANCIAL CORPORATION

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

                                      -15-
<PAGE>

         Each of the undersigned hereby (a) consents to execution by the
Borrower of this Amendment and (b) confirms that each Loan Document now or
previously executed by it applies and shall continue to apply to the Credit
Agreement and shall continue a Loan Document.

                                           EACH OF THE SUBSIDIARIES OF AMERICAN
                                           PLUMBING & MECHANICAL, INC.

                                           By:
                                              ---------------------------------
                                           Name:
                                                -------------------------------
                                           Title:
                                                 ------------------------------
                                                  of each of such subsidiaries

Schedule I - Pricing Schedule
Schedule III - Listing of Subsidiaries and Ownership
Appendix A - Commitments
Appendix B - Discontinued Operations
Appendix C - Projections

                                      -16-
<PAGE>
                                   APPENDIX A

                                   COMMITMENTS

<Table>
<Caption>
                                                              December 31, 2002
                                             Through               Through            On and After
 Lender                                 December 30, 2002     December 30, 2003      December 31,2003
 ------                                 -----------------     -----------------      ----------------
<S>                                      <C>                   <C>                   <C>
Bank One, NA                             $     23,684,211      $     22,368,421      $     21,052,632

Credit Lyonnais                          $     23,684,211      $     22,368,421      $     21,052,632
New York Branch

Union Bank of                            $     18,947,368      $     17,894,738      $     16,842,105
California, N.A

Fleet National Bank                      $      9,473,684      $      8,947,368      $      8,421,053

Comerica Bank                            $      7,105,263      $      6,710,526      $      6,315,789

Bay View Financial Corporation           $      7,105,263      $      6,710,526      $      6,315,789
</Table>

<PAGE>

                                   SCHEDULE I

                                PRICING SCHEDULE

<Table>
<S>                                                    <C>
Applicable Margin
(per annum):  Eurodollar Advance:
              Eurodollar Base Rate,                     4.00%
                 plus

Applicable Margin
(per annum):  Floating Rate Advance:
              Alternate Base Rate,
                 plus                                   3.00%

Commitment Fees
(per annum):                                            0.50%

LC Fee
(per annum):                                            4.00%
</Table><PAGE>
                                                                     EXHIBIT 4.4

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

                             NABORS HOLDING COMPANY

                                       AND

                           THE GUARANTORS NAMED HEREIN

                              SERIES A AND SERIES B

                    8 5/8% SENIOR SUBORDINATED NOTES DUE 2008

                              --------------------

                          FOURTH SUPPLEMENTAL INDENTURE

                            DATED AS OF JUNE 21, 2002

                              --------------------

                                 HSBC BANK USA,

                                     TRUSTEE

                              --------------------

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

<PAGE>

                  This FOURTH SUPPLEMENTAL INDENTURE (this "Supplemental
Indenture"), dated as of June 21, 2002 is among Nabors Holding Company, a
Delaware corporation, as issuer (the "Company"), Nabors Industries, Inc., a
Delaware corporation, as guarantor (the "Parent Guarantor"), Nabors Industries
Ltd., a Bermuda exempted company, as guarantor (the "New Guarantor"), and HSBC
Bank USA, as trustee (the "Trustee").

                                    RECITALS

                  WHEREAS, the Company, and the Trustee entered into an
Indenture, dated as of March 31, 1998 (as supplemented by each of the three
supplemental indentures thereto, including one relating to the guarantee of the
Company's obligations thereunder by the Parent Guarantor, the "Indenture"),
pursuant to which the Company has originally issued $150,000,000 in principal
amount of 8 5/8% Senior Subordinated Notes due 2008 (the "Notes"); and

                  WHEREAS, the Parent Guarantor is party to an Agreement and
Plan of Merger, dated as of January 2, 2002, by and among the Company, the New
Guarantor, Nabors US Holdings Inc., a corporation duly organized and existing
under the laws of the State of Delaware (herein called "US Holdings") and Nabors
Acquisition Corp. VIII, a corporation duly organized and existing under the laws
of the State of Delaware (herein called "NAC8") (such agreement is herein called
the "Merger Agreement");

                  WHEREAS, US Holdings assigned all of its right, title and
interest, in, to and under the Merger Agreement to Nabors International Finance
Ltd., an exempted company duly organized and existing under the laws of the
Islands of Bermuda, and NAC8 assigned all of its right, title and interest, in,
to and under the Merger Agreement to Nabors Acquisition Corp. IX, a corporation
duly organized and existing under the laws of the State of Delaware (herein
called "NAC9");

                  WHEREAS, pursuant to the terms and conditions of the Merger
Agreement, NAC9 will merge with and into Parent Guarantor, with Parent Guarantor
being the surviving corporation (herein called the "Merger" and the date on
which the Merger becomes effective by filing a Certificate of Merger with the
Secretary of State of the State of Delaware is herein called the "Merger Date");

                  WHEREAS, as a result of the Merger the Parent Company will be
an indirect, wholly owned subsidiary of the New Guarantor;

                                       2
<PAGE>

                  WHEREAS, the New Guarantor desires to issue a guarantee to the
Holders of the Notes as provided in this Supplemental Indenture;

                  WHEREAS, Section 9.01(iv) provides that the Company, the
Parent Guarantor and the Trustee may amend or supplement the Indenture or the
Notes without the consent of any Holders to make any change that would provide
any additional rights or benefits to the Holders;

                  WHEREAS, the respective Board of Directors of the Company, the
Parent Guarantor and of the New Guarantor (or a duly authorized committee
thereof) has duly adopted resolutions authorizing the Company, the Parent
Guarantor and the New Guarantor, respectively, to execute and deliver this
Supplemental Indenture; and

                  WHEREAS, all acts and things prescribed by the Indenture, by
law and by the charter and the bylaws (or comparable constituent documents) of
the Company, of the Parent Guarantor, of the New Guarantor and of the Trustee
necessary to make this Supplemental Indenture a valid instrument legally binding
on the Company, the Parent Guarantor, the New Guarantor and the Trustee, in
accordance with its terms, have been duly done and performed;

                  NOW, THEREFORE, to comply with the provisions of the Indenture
and in consideration of the above premises, the Company, the Parent Guarantor,
the New Guarantor and the Trustee covenant and agree for the equal and
proportionate benefit of the respective Holders of the Notes as follows:

                                   ARTICLE ONE

                              RELATION TO INDENTURE

         SECTION 1.1 RELATION TO INDENTURE.

         This Supplemental Indenture constitutes an integral part of the
Indenture.

         SECTION 1.2 DEFINITIONS.

         For all purposes of this Supplemental Indenture, except as expressly
provided for or unless the context otherwise requires:

                                       3
<PAGE>

                  (1) Capitalized terms used but not defined in this
Supplemental Indenture shall have the respective meanings assigned to them in
the Indenture; and

                  (2) All references in this Supplemental Indenture to Articles
and Sections, unless otherwise specified, refer to the corresponding Articles
and Sections of this Supplemental Indenture.

         SECTION 1.3 AMENDMENT OF DEFINITIONS IN THE INDENTURE.

         The following definitions in the Indenture are hereby amended by
deleting such definitions in their entirety and substituting in place thereof
the following:

         "BOARD RESOLUTION" means a copy of a resolution certified by the
Secretary of the Company, the Parent Guarantor or the New Guarantor, as
applicable, duly adopted by the Board of Directors of such Person and to be in
full force and effect on the date of such certification, and delivered to the
Trustee.

         "GUARANTOR" means each of the Parent Guarantor and the New Guarantor
and any and all references to "the Guarantor", "a Guarantor" or "any Guarantor"
shall refer to each of the Parent Guarantor and the New Guarantor.

         "OFFICERS" means any of the following of any Guarantor or the Company,
as applicable: the Chairman of the Board, the Chief Executive Officer, the Chief
Financial Officer, the President, any Vice President, the Treasurer or the
Secretary.

         "OPINION OF COUNSEL" means a written opinion from legal counsel (such
counsel may be an employee of or counsel to the Company or any Guarantor) that
complies with the requirements of this Indenture.

         "SENIOR INDEBTEDNESS" means all Indebtedness and other Obligations
specified below payable directly or indirectly by any Guarantor, as the case may
be, whether outstanding on the Issue Date, as of the date of the Fourth
Supplemental Indenture hereto or thereafter created, incurred or assumed by any
Guarantor: (i) the principal of and interest on and all other Indebtedness and
Obligations related to the Credit Agreement (including, without limitation, all
loans, letters of credit and unpaid drawings with respect thereto and other
extensions of credit under the Credit Agreement, and all expenses, fees,
reimbursements, indemnities and other amounts owing pursuant to the Credit
Agreement), (ii) amounts payable in respect of any Hedging Obligations, (iii) in
addition to the amounts described in (i) and (ii), all Indebtedness that is not
expressly pari passu with, or subordinated to, the Notes or a Note Guarantee, as
the case may be, (iv) all Capitalized Lease Obligations, (v) all Refinancing
Indebtedness permitted under this Indenture. Notwithstanding anything to the
contrary in the foregoing, Senior Indebtedness will not include (a) any
Indebtedness which by the express terms of the agreement or instrument creating,
evidencing or governing the same is junior or subordinate in right of payment to
any item of Senior Indebtedness, (b) any trade payable arising from the purchase
of goods or materials or for services obtained in the ordinary course of
business, (c) Indebtedness incurred (but only to the extent incurred) in
violation of this Indenture as in effect at the time of the respective
incurrence, (d) any Indebtedness of any Guarantor or any of

                                       4
<PAGE>

its Subsidiaries that, when incurred, was without recourse to such Guarantor or
any of its Subsidiaries, (e) any Indebtedness to any employee of any Guarantor
or any of its Subsidiaries or (f) any liability for taxes owed or owing by any
Guarantor or any of its Subsidiaries.

         The Indenture is hereby amended by adding the following definition
thereto:
         "NEW GUARANTOR" means Nabors Industries Ltd., an exempted company duly
organized and existing under the laws of the Islands of Bermuda.

                                   ARTICLE TWO

                              REPORTS BY GUARANTOR

         Section 2.1 Reports. Section 4.02 of the Indenture is hereby amended by
deleting it in its entirety and substituting in place thereof the following:

                           Section 4.02. Reports. Whether or not required by the
                  rules and regulations of the Securities and Exchange
                  Commission (the "COMMISSION"), so long as any Notes are
                  outstanding, the New Guarantor will file with the Commission,
                  to the extent such filings are accepted by the Commission, and
                  will furnish (within 15 days after such filing) to the Trustee
                  and the Holders of Notes all quarterly and annual reports and
                  other information, documents and reports that would be
                  required to be filed with the Commission pursuant to Section
                  13 of the Exchange Act (including therein any summary or other
                  information with respect to the Company as may be required
                  thereby, taking into account the guarantee by the New
                  Guarantor) if the New Guarantor was required to file under
                  such section.

                           So long as any Notes are outstanding, the Company and
                  the Parent Guarantor will file with the Commission, to the
                  extent such filings are required by the Commission, and will
                  furnish (within 15 days after such filing) to the Trustee and
                  the Holders of Notes all quarterly and annual reports and
                  other information, documents and reports that are required to
                  be filed with the Commission pursuant to Section 13 of the
                  Exchange Act (including therein any summary or other
                  information with respect to the Company as may be required
                  thereby, taking into account the guarantee by the New
                  Guarantor).

                                       5
<PAGE>

                           The Company, the Parent Guarantor and the New
                  Guarantor will make the foregoing information available to
                  prospective purchasers of the Notes, securities analysts and
                  broker-dealers who request it in writing. The Company and each
                  Guarantor have agreed that, for so long as any Notes remain
                  outstanding, they will furnish to the Holders and beneficial
                  Holders of Notes and to prospective purchasers of Notes
                  designated by the Holders and to broker dealers, upon their
                  request, the information required to be delivered pursuant to
                  Rule 144A(d)(4) under the Securities Act.

                                  ARTICLE THREE

                            CERTIFICATE OF COMPLIANCE

         SECTION 3.1 STATEMENT BY OFFICERS AS TO COMPLIANCE. Section 4.03 of the
Indenture is hereby amended by deleting it in its entirety and substituting in
place thereof the following:

                           Section 4.03. Compliance Certificate. The Company,
                  the Parent Guarantor and the New Guarantor shall each deliver
                  to the Trustee, within 120 days after the end of each fiscal
                  year of the Company, an Officers' Certificate stating that (i)
                  a review of the activities of the Company and its Subsidiaries
                  during the preceding fiscal year without regard to any Grace
                  Period has been made to determine whether the Company, the
                  Parent Guarantor and the New Guarantor have kept, observed,
                  performed and fulfilled all of their obligations under this
                  Indenture and the Notes, (ii) such review was supervised by
                  the Officers of the Company, the Parent Guarantor and the New
                  Guarantor signing such certificate, and (iii) to the best
                  knowledge of each Officer signing such certificate, (a) the
                  Company, the Parent Guarantor or the New Guarantor, as
                  applicable, has kept, observed, performed and fulfilled each
                  and every covenant contained in this Indenture applicable to
                  such person and such person is not in default in the
                  performance or observance of any of the terms, provisions and
                  conditions of this Indenture applicable to such person (or, if
                  a Default or Event of Default occurred, describing all such
                  Defaults or Events of Default of which each such Officer may
                  have knowledge and what action the Company, the Parent
                  Guarantor and the New Guarantor, as applicable, have taken or
                  propose to take with respect thereto), and (b) no event has
                  occurred and remains in existence by

                                       6
<PAGE>
                  reason of which payments on account of the principal of, or
                  premium, if any, or interest (including Special Interest, if
                  any) on the Notes are prohibited or if such event has
                  occurred, a description of the event and what action the
                  Company, the Parent Guarantor and the New Guarantor, as
                  applicable, are taking with respect thereto.

                           Each of the Company, the Parent Guarantor and the New
                  Guarantor will, so long as any of the Notes are outstanding,
                  deliver to the Trustee, promptly after any Officer of the
                  Company, the Parent Guarantor or the New Guarantor becomes
                  aware of any Default or Event of Default, an Officers'
                  Certificate specifying such Default or Event of Default and
                  what action the Company, the Parent Guarantor or the New
                  Guarantor is taking or proposes to take with respect thereto.

                                  ARTICLE FOUR

                                    GUARANTEE

         SECTION 4.1 GUARANTEE.

         By execution of this Supplemental Indenture, the New Guarantor hereby
issues and provides for a Note Guarantee on the terms and conditions, and to the
extent, set forth in Section 11.01 of the Indenture. The Note Guarantees of the
Parent Guarantor and the New Guarantor shall be joint and several.

         SECTION 4.2 SUBORDINATION OF GUARANTEE.

         The New Guarantor's Note Guarantee shall be junior and subordinated in
right of payment to any Senior Indebtedness to the extent provided in Section
11.03 and Article 10 of the Indenture.

                                       7
<PAGE>

                                  ARTICLE FIVE

                            MISCELLANEOUS PROVISIONS

         SECTION 5.1 RATIFICATION OF INDENTURE.

         Except as expressly modified or amended hereby, the Indenture continues
in full force and effect and is in all respects confirmed and preserved.

         SECTION 5.2 EFFECTIVENESS.

         This Fourth Supplemental Indenture shall be effective as of the date
first written above, provided, however, that the provisions contained in
Articles One, Two, Three and Four hereof shall become effective as of the Merger
Date. In the event that the Merger Agreement is terminated in accordance with
its terms, this Fourth Supplemental Indenture shall automatically become null
and void and the Company, the Parent Guarantor and the Trustee shall continue to
comply with the Indenture. On or promptly following the Merger Date, the New
Guarantor shall furnish to the Trustee an Officers' Certificate certifying that
the Merger has occurred and that Articles One, Two, Three and Four hereof have
become effective.

         SECTION 5.3 ADDRESS OF TRUSTEE.

         Section 12.02 of the Indenture is hereby amended to provide that the
address of the Trustee is:

                         HSBC Bank USA
                         452 Fifth Street
                         New York, New York 10018
                         Attention: Issuer Services

         SECTION 5.4 GOVERNING LAW.

         THIS SUPPLEMENTAL INDENTURE AND THE NOTE GUARANTEE SHALL BE GOVERNED BY
AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, WITHOUT
REGARD TO PRINCIPLES OF CONFLICTS OF LAWS. This Supplemental Indenture is
subject to the provisions of the Trust Indenture Act and shall, to the extent
applicable, be governed by such provisions.

         SECTION 5.5 COUNTERPARTS.

         This Supplemental Indenture may be executed in any number of
counterparts, each of which shall be an original, but all such counterparts
shall together constitute but one and the same instrument.

         SECTION 5.6 CERTAIN RIGHTS OF TRUSTEE.

         Except as otherwise provided herein, no duties, responsibilities or
liabilities are assumed, or shall be construed to be assumed, by the Trustee by
reason of this Supplemental Indenture. This Supplemental Indenture is executed
and accepted by the Trustee subject to all the terms and conditions set forth in
the Indenture with the same force and effect as if those terms and conditions
were repeated at length herein and made applicable to the Trustee with respect
hereto.

                                       8
<PAGE>

         SECTION 5.7 TRUSTEE NOT RESPONSIBLE FOR RECITALS.

         The Trustee shall not be responsible in any manner for or in respect of
the validity or sufficiency of this Supplemental Indenture, or for or in respect
of the recitals contained herein, all of which recitals are made by the Company
and the Guarantor.

                            [SIGNATURE PAGE FOLLOWS]

                                       9
<PAGE>

                  IN WITNESS WHEREOF, the parties hereto have caused this Fourth
Supplemental Indenture to be duly executed, all as of the date first written
above.

                                 ISSUER:

                                 NABORS HOLDING COMPANY

                                 By:  /s/ Anthony G. Petrello
                                      Anthony G. Petrello
                                      President

                                 GUARANTORS:

                                 NABORS INDUSTRIES, INC.

                                 By:  /s/ Anthony G. Petrello
                                      Anthony G. Petrello
                                      President & Chief Operating Officer

                                 NABORS INDUSTRIES LTD.

                                 By:  /s/ Bruce P. Koch
                                      Bruce P. Koch
                                      Vice President--Finance

                                 HSBC BANK USA,
                                 as Trustee

                                 By:  /s/ Frank J. Godino
                                      Name: Frank J. Godino
                                      Title: Vice President

                                       10

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