<PAGE>
                                                                  EXHIBIT 10.45


                       SEVENTH AMENDMENT TO LOAN AGREEMENT


         THIS SEVENTH AMENDMENT TO LOAN AGREEMENT (this "Amendment"), dated as
of March 11, 2004, is between HORIZON OFFSHORE CONTRACTORS, INC., a Delaware
corporation ("Contractors"), HORIZON SUBSEA SERVICES, INC., a Delaware
corporation ("Subsea"), and HORIZON VESSELS, INC., a Delaware corporation
("Vessels", and together with Contractors and Subsea the "Borrowers"), jointly
and severally, each of the financial institutions which is or may from time to
time become a party to such Loan Agreement, as amended (collectively, "Lenders",
and each a "Lender"), and SOUTHWEST BANK OF TEXAS, N.A., a national banking
association, as agent (the "Agent").

                                    RECITALS:

         A. Borrowers, Lenders and Agent entered into that certain Loan
Agreement dated as of March 26, 2001, as amended by First Amendment to Loan
Agreement dated as of April 17, 2002, Second Amendment to Loan Agreement dated
as of May 30, 2002, Third Amendment to Loan Agreement dated as of August 28,
2002, Fourth Amendment to Loan Agreement dated as of September 30, 2002, Fifth
Amendment to Loan Agreement dated as of March 6, 2003 and Sixth Amendment to
Loan Agreement dated as of January 30, 2004 (the "Agreement").


         A. Pursuant to the Agreement, Horizon Offshore, Inc., a Delaware
corporation ("Guarantor"), executed a Guaranty dated as of March 26, 2001 (the
"Guaranty") pursuant to which Guarantor guaranteed to Agent the payment and
performance of the Obligations (as defined in the Agreement).

         B. Pursuant to the Agreement all the other subsidiaries of Guarantor
executed guaranty agreements pursuant to which such Subsidiaries guaranteed the
obligations of Borrowers under the Loan Agreement.

         C. Borrowers, Lenders and Agent now desire to amend the Agreement as
herein set forth.

         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:

                                   1. ARTICLE

                                   Definitions

         1.1. Section Definitions. Capitalized terms used in this Amendment, to
the extent not otherwise defined herein, shall have the meanings given to such
terms in the Agreement, as amended hereby.

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                                   2. ARTICLE

                                   Amendments

         2.1. Section Amendment to Certain Definitions. (a) The definition of
each of the following terms contained in Section 1.1 of the Agreement is amended
to read in its respective entirety as follows:

         "Applicable Rate" means the sum of the Prime Rate plus (a) one percent
         (1.00%) from March 11, 2004 through June 29, 2004, (b) one and one-half
         percent (1.50%) from June 30, 2004 through September 29, 2004, (c) two
         percent (2.00%) from September 30, 2004 through December 30, 2004, and
         (d) two and one-half percent (2.50%) from December 31, 2004 through the
         Termination Date; provided, however, that in no event shall the
         Applicable Rate be less than five percent (5.00%).

         "Current Liabilities" means all amounts which, in conformity with GAAP,
         would be included as current liabilities on a consolidated balance
         sheet of Guarantor and its Subsidiaries, excluding all revolving credit
         facilities.

         "Current Maturities of Long Term Debt" means for Guarantor and its
         Subsidiaries on a consolidated basis, the principal amount due and
         payable during the next succeeding twelve month period on Total Funded
         Debt of Guarantor and its Subsidiaries which has a final maturity more
         than twelve months from the date of calculation, excluding all
         revolving credit facilities.

         "EBITDA" means, for Guarantor and its Subsidiaries, on a consolidated
         basis, for any period, the sum of (a) Net Income before gains and
         losses on sales of assets (to the extent such gains and losses are
         included in earnings), plus (b) Tax Expense, plus (c) depreciation and
         amortization, plus (d) Interest Expense.

         "Fixed Charge Coverage Ratio" means for Guarantor and its Subsidiaries,
         on a consolidated basis, (a) as of September 30, 2004, (i) EBITDA for
         the quarter ended as of September 30, 2004, divided by (ii) the sum of
         (A) Current Maturities of Long Term Debt as of September 30, 2004
         divided by four (4), plus (B) Interest Expense for the quarter ended as
         of September 30, 2004, plus (C) Tax Expense for the quarter ended as of
         September 30, 2004, and (b) as of December 31, 2004, (i) EBITDA for the
         quarters ended as of September 30, 2004 and December 31, 2004, divided
         by (ii) the sum of (A) Current Maturities of Long Term Debt as of
         December 31, 2004 divided by two (2), plus (B) Interest Expense for the
         quarters ended as of September 30, 2004 and December 31, 2004, plus (C)
         Tax Expense for the quarters ended as of September 30, 2004 and
         December 31, 2004.


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         "Foreign Loan Agreement" means that certain EXIM Guaranteed Loan
         Agreement among Borrowers, LLC, the Foreign Agent and the lenders
         referred to therein, as amended by First Amendment to EXIM Guaranteed
         Loan Agreement dated April 17, 2002, Second Amendment to EXIM
         Guaranteed Loan Agreement dated August 28, 2002, Third Amendment to
         EXIM Guaranteed Loan Agreement dated September 30, 2002, Fourth
         Amendment to EXIM Guaranteed Loan Agreement dated March 6, 2003, Fifth
         Amendment to EXIM Guaranteed Loan Agreement dated January 30, 2004 and
         Sixth Amendment to EXIM Guaranteed Loan Agreement dated March 11, 2004,
         and as the same may be further amended, supplemented or modified from
         time to time, and any loan agreement or credit agreement executed in
         restatement and replacement therefor.

         "Net Income" means, for any period, with respect to Guarantor and its
         Subsidiaries, the consolidated net income (or loss) of Guarantor and
         its Subsidiaries for such period, determined in accordance with GAAP
         applied consistently (excluding any extraordinary items during such
         period).

         "Prime Rate" means, at any time, the rate of interest per annum then
         most recently published in The Wall Street Journal (or any successor
         publication if The Wall Street Journal is no longer published) in the
         "Money Rates" section (or such successor section) as the "Prime Rate."
         If a range of prime interest rates per annum is so published, "Prime
         Rate" shall mean the highest rate per annum in such published range. If
         the definition of "Prime Rate" is no longer published in The Wall
         Street Journal (or any successor publication), "Prime Rate" shall mean,
         at any time, the rate of interest per annum then most recently
         established by Lender as its prime rate.

         "Tangible Net Worth" means, at any particular date, all amounts which,
         in conformity with GAAP, would be included as stockholders' equity on a
         consolidated balance sheet of Guarantor and its Subsidiaries; provided,
         however, there shall be excluded therefrom (a) any amount at which
         shares of capital stock of Guarantor or any Subsidiary appear as an
         asset on Guarantor's or such Subsidiary's balance sheet, (b) goodwill,
         including any amounts, however designated, that represent the excess of
         the purchase price paid for assets or stock over the value assigned
         thereto, (c) patents, trademarks, trade names, and copyrights, (d)
         deferred expenses, (e) loans and advances to any stockholder, director,
         officer, or employee of Guarantor or any Subsidiary or any Affiliate,
         (f) all other assets which are properly classified as intangible assets
         and (g) paid-in-kind interest on the New Subordinated Debt.

         "Termination Date" means 11:00 a.m., Houston, Texas time on January 21,
         2005, or such earlier date on which the Commitment terminates as
         provided in this Agreement.

         (b) The following phrase shall be added to the end of the first
sentence of the definition of the term "Eligible Accounts":


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         "and (r) have not been determined to be ineligible or not to constitute
         Eligible Accounts by the Majority Lenders, which determination shall be
         made by the Majority Lenders in their sole discretion."

         (c) The following definitions shall be added to Section 1.1 of the
Agreement in proper alphabetical order:

         "EBITDAR" means, for Guarantor and its Subsidiaries, on a consolidated
         basis, for any period, the sum of (a) Net Income before gains and
         losses on sales of assets (to the extent such gains and losses are
         included in earnings), plus (b) Tax Expense, plus (c) depreciation and
         amortization, plus (d) Interest Expense, plus (e) restructuring
         charges, including costs of professional advisors to Borrowers (for the
         professional advisors to the Borrowers, the Lenders or other creditors)
         not to exceed $1,600,000.00 for the fiscal year ending December 31,
         2004.

         "Iroquois" means Iroquois Gas Transmission System, L.P., and its
         successors and assigns.

         "Iroquois Contract" means that certain contract No. 02-12 dated April
         12, 2002 between Iroquois and Contractors.

         "New Subordinated Debt" means Debt of Guarantor evidenced by its 16%
         Subordinated Secured Notes due March 31, 2007, issued pursuant to the
         Purchase Agreement in an original principal amount not less than
         $65,400,000.00, the payment of which is subordinate to the payment of
         the Obligations in a manner satisfactory to Agent and all other terms
         of which (including interest rate, maturity, payment terms to the
         effect that no cash payments may be made thereon for principal,
         interest or fees (except for payments of principal paid solely from (i)
         proceeds of Pemex Contract EPC-64 or the Williams Contract, or (ii)
         proceeds of any issuance of equity), financial covenants and
         collateral) are acceptable to Agent and the Majority Lenders.

         "Pemex" means Pemex-Exploracion y Produccion, a decentralized public
         organization of the federal government of the United States of Mexico
         and a subsidiary of Petroleos Mexicanos.

         "Pemex Contract EPC-64" means that certain contract No. PEP-0-AD-317/00
         (also known as EPC-64) between Pemex and ECH.

         "Purchase Agreement" means that certain Purchase Agreement dated March
         11, 2004, among Guarantor, the guarantors listed therein and the
         purchasers listed therein, pursuant to which the New Subordinated Debt
         was issued, as the same may be amended, supplemented or modified from
         time to time.


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         "Tax Expense" means, for any period, for Guarantor and its
         Subsidiaries, on a consolidated basis, the sum of all tax expense of
         Guarantor and its Subsidiaries for such period determined in accordance
         with GAAP applied consistently.

         "Williams" means Williams Oil Gathering, L.L.C., and its successors
          and assigns.

         "Williams Contract" means that certain contract between Williams and
         Contractors for Subsea Shallow Water Pipelay of the 20-inch Oil
         Mountaineer Pipeline on Devil's Tower Project from Main Pass Block 313
         to main Pass Block 22, effective as of October 1, 2002.

         (d) The definition of the following terms shall be deleted from Section
1.1 of the Agreement:

                  "Applicable Margin"
                  "Cash Taxes"
                  "Continue", "Continuation" and "Continued"
                  "Convert", "Conversion", and "Converted"
                  "Interest Period"
                  "LIBOR Advances"
                  "LIBOR Margin"
                  "LIBOR Rate"
                  "London Business Day"
                  "Prime Rate Advances"
                  "Prime Rate Margin"
                  "Ratio of Funded Debt to Capitalization"
                  "Ratio of Funded Debt to EBITDA"
                  "Total Capitalization"
                  "Type"
                  "Working Capital"

         2.2. Section Amendment to Section 2.4. Section 2.4 of the Agreement is
amended to read in its entirety as follows:

         Section 2.4. Interest. The unpaid principal amount of the Advances
         shall bear interest prior to maturity at a varying rate per annum equal
         from day to day to the lesser of (a) the Maximum Rate or (b) the
         Applicable Rate, and each change in the rate of interest charged on the
         Advances shall become effective, without notice to Borrowers, on the
         effective date of each change in the Applicable Rate or the Maximum
         Rate, as the case may be; provided, however, if at any time the rate of
         interest specified in clause (b) preceding shall exceed the Maximum
         Rate, thereby causing the interest on the Advances to be limited to the
         Maximum Rate, then any subsequent reduction in the Applicable Rate
         shall not reduce the rate of interest on the Advances below the Maximum
         Rate until the aggregate amount of interest accrued on the Advances
         equals the aggregate amount of interest which would have accrued on the
         Advances if the interest rate specified in clause (b) preceding had at
         all times been in effect. Accrued and unpaid interest on the


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         Advances shall be payable on the first day of each month commencing
         on April 1, 2004, and on the Termination Date.

         Notwithstanding the foregoing, if any Event of Default has occurred and
         is continuing, the outstanding principal of the Advances shall bear
         interest at the Default Rate. Interest payable at the Default Rate
         shall be payable from time to time on demand.

         2.3. Section Amendment to Section 2.5. Section 2.5 of the Agreement is
amended to read in its entirety as follows:

         Section 2.5. Requests for Advances. Borrowers shall give Agent notice
         of each requested Advance by delivery to Agent of an Advance Request
         Form executed by an Authorized Representative at least one (1) Business
         Day before the requested date of each Advance. Advance Request Forms
         may be delivered by fax. Prior to making any Advance, Agent may require
         that Borrowers deliver a Borrowing Base Certificate dated a recent date
         acceptable to Agent evidencing that the amount of the outstanding
         Advances plus the requested Advance plus the Letter of Credit
         Liabilities is less than the lesser of (a) the Combined Commitments or
         (b) the Borrowing Base. The Agent shall promptly notify each Lender of
         the contents of each such notice. No later than 11:00 a.m. Houston,
         Texas time on the date specified for each Advance hereunder, each
         Lender shall make available to Agent at its office specified herein in
         immediately available funds, its Pro Rata Share of each Advance. After
         Agent's receipt of such funds and subject to the other terms and
         conditions of this Agreement, Agent shall make each Advance available
         to the Borrowers by depositing the same, in immediately available
         funds, in the operating account of Contractors maintained at Agent's
         office specified herein. Advance Request Forms submitted shall be
         irrevocable and shall be effective for the requested Advances on the
         following Business Day if received by Agent by 11:00 a.m. Houston,
         Texas time on a Business Day, and otherwise on the next following
         Business Day.

         2.4. Section Amendment to Section 2.7. (a) Clause (a) is inserted
before the existing text in Section 2.7 of the Agreement.

         (b) Clause (b) shall be added to Section 2.7 of the Agreement and shall
read in its entirety as follows:

         (b) On any date on which Borrowers receive payment of the Iroquois
         Contract, the Advances shall be due and payable in a principal amount
         equal to one hundred percent (100%) of the net proceeds of such payment
         (excluding payments to subcontractors).

2.5. Section Amendment to Section 2.8. The phrase "payable monthly on the
thirtieth (30th) day of each month (or the last day of February)," contained in
the first sentence of Section 2.8 of the Agreement is amended to read "payable
monthly on the first (1st) day of each month,".


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         2.6. Section Amendment to Section 2.10. Clause (a) contained in the
second sentence of Section 2.10 of the Agreement is amended to read in its
entirety as follows:

         (a) have an expiration date which is at least ten (10) days prior to
         the Termination Date, unless such Letter of Credit is specifically
         secured by cash in an amount at least equal to one hundred percent
         (100%) of the face amount of such Letter of Credit,

         2.7. Section Amendment to Section 2.14. The first sentence contained in
Section 2.14 of the Agreement is amended to read in its entirety as follows:

         Borrowers shall pay to the Agent for the Pro Rata benefit of the
         Lenders a letter of credit fee payable on the date each Letter of
         Credit is issued in an amount equal to the greater of (a) three and
         one-quarter percent (3.25%) per annum of the stated amount of such
         Letter of Credit for the period during which such Letter of Credit will
         remain outstanding, based on a 360 day year and the actual number of
         days elapsed, or (b) $350.00.

         2.8. Section Amendments to Article III. (a) The phrase "Additional
Matters with Respect to LIBOR Loans" shall be deleted from the title of Article
III of the Agreement.

         (b) The phrase "other than the amounts described in Section 3.9" shall
be deleted from Section 3.3 of the Agreement.

         (c)      Section 3.4 of the Agreement is amended to read in its
                  entirety as follows: Section 3.4. Computation of Interest.
                  Interest on the indebtedness evidenced by the Notes shall be
                  computed on the basis of a year of (a) 360 days and the actual
                  number of days elapsed (including the first day but excluding
                  the last day) unless such calculation would result in a
                  usurious rate, in which case interest shall be calculated on
                  the basis of a year of 365 or 366 days, as the case may be.

         (d)      Sections 3.7, 3.8 and 3.9 shall be deleted from the Agreement
                  in their entirety.

         2.9. Section Addition of Section 4.5. Section 4.5 shall be added to the
Agreement and shall read in its entirety as follows:

         Section 4.5. Pemex Contract EPC-64; Williams Contract. Agent shall, at
         the option of the holders of the New Subordinated Debt, (a) assign its
         Liens in the Williams Contract to the holders of the New Subordinated
         Debt, and (b) terminate its Liens in the Pemex Contract EPC-64, and,
         concurrently therewith, the Pemex Contract EPC-64 shall be removed from
         the Borrowing Base, as defined in the Foreign Loan Agreement.


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         2.10. Section Amendment to Section 7.1. The phrase "within forty-five
(45) days after the end of each quarter of each fiscal year" contained in clause
(b) of Section 7.1 of the Agreement is amended to read "within forty-five (45)
days after the end of the first three (3) quarters of each fiscal year".

         2.11. Section Amendment to Section 8.1. Section 8.1 of the Agreement is
amended to read in its entirety as follows:

         Section 8.1. Debt. No Borrower will incur, create, assume or permit to
         exist, nor will any Borrower permit Guarantor or any Subsidiary to
         incur, create, assume, or permit to exist, any Debt, except

         (a) indebtedness of Borrowers to Lenders under this Agreement and the
         Loan Documents;

         (b) Indebtedness of Borrowers under the Foreign Loan Agreement in an
         aggregate principal amount such that the sum of the maximum permitted
         Indebtedness of Borrowers under the Foreign Loan Agreement plus the
         Combined Commitments does not exceed $50,000,000.00;

         (c) accounts payable and accrued liabilities incurred in the ordinary
         course of business;

         (d) letter of credit, performance and bid bonds obtained by Borrowers
         in the ordinary course of their business, other than the Letters of
         Credit, up to an aggregate amount of $15,000,000.00 at any time;

         (e) supersedeas bonds obtained by Borrowers in the ordinary course of
         their business;

         (f) secured term indebtedness existing on December 31, 2003

         (g) Committed indebtedness of Borrowers under the CIT Loan Agreement
         and other committed indebtedness of Borrowers secured only by vessels,
         in each case existing on December 31, 2003; and

         (h) the New Subordinated Debt.

         2.12. Section Amendment to Section 8.2. Section 8.2 of the Agreement is
amended to read in its entirety as follows:

         Section 8.2 Limitation on Liens. No Borrower will incur, create, assume
         or permit to exist, nor will any Borrower permit Guarantor, or any
         Subsidiary any Qualified Foreign Subsidiary or any Related Entity to
         incur, create, assume or permit to exist, any Lien upon any of its
         property, assets or revenues, whether now owned or hereafter acquired,
         except for the liens and other encumbrances set forth below (the
         "Permitted Liens"):


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<PAGE>

         (a) Liens for Taxes (i) not at the time delinquent or (ii) being
         contested in good faith and by appropriate proceedings and with respect
         to which proper reserves have been taken by Borrower, such Subsidiary
         or such Qualified Foreign Subsidiary, provided that such Liens shall
         have no effect upon the priority of the Liens in favor of Agent or the
         value of the Collateral and a stay of enforcement if any such Lien
         shall be in effect;

         (b) Liens of carriers, warehousemen, mechanics, materialmen and
         landlords incurred in the ordinary course of business with respect to
         obligations which are not due;

         (c) maritime Liens:

              (i)  arising in the ordinary course of business by operation of
                   law that are being contested in good faith by appropriate
                   proceedings and for which reserves have been established to
                   the reasonable satisfaction of Lenders or

             (ii)  arising in connection with salvage and general average; or

            (iii)  arising in connection with crew wages claimed but not paid;
                   provided that such maritime Liens do not attach to the
                   Collateral with respect to which Agent is to have a first
                   priority Lien as provided in Section 4.1;

         (d) Liens incurred in the ordinary course of business in connection
         with workmen's compensation, unemployment insurance or other forms of
         governmental insurance or benefits, or to secure performance of tenders
         and statutory obligations entered into in the ordinary course of
         business or to secure obligations on surety or appeal bonds in the
         ordinary course of business or easements, rights of way and similar
         encumbrances incurred in the ordinary course of business and not
         interfering with the ordinary conduct of the business of any Borrower,
         Guarantor, any Subsidiary, any Qualified Foreign Subsidiary or any
         Related Entity;

         (e) judgment Liens, the execution of which has been stayed or which are
         bonded, provided that, if bonded, the payment of such judgment Liens is
         fully covered by insurance and the insurance carrier has acknowledged
         such coverage in writing;

         (f) Liens required by the terms of this Loan Agreement;

         (g) Liens in favor of the Foreign Agent pursuant to the Foreign Loan
         Agreement, provided that such Liens also secure the Obligations; and
         provided, further, that only the Liens covering the Export-Related
         Accounts Receivable, the Export-Related Inventory, the Export-Related


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<PAGE>

         General Intangibles and the Other Foreign Collateral shall be prior to
         the Liens of Agent under this Agreement and the Loan Documents;

         (h) Liens in connection with Debt referred to in Section 8.1(f),
         provided that such Liens do not cover any of the Collateral;

         (i) Liens on vessels created in accordance with the CIT Loan Agreement
         securing the indebtedness of Borrowers under the CIT Loan Agreement and
         Liens on vessels securing other Debt permitted pursuant Section 8.1(g);

         (j) Permitted Liens as defined in the Borrower Agreement; and

         (k) Liens securing the New Subordinated Debt created as of the date of
         the Seventh Amendment to Loan Agreement (amending this Agreement),
         provided that such Liens do not attach to any of the Collateral (as the
         Collateral exists after the assignments and terminations executed by
         the Agent in connection with the incurrence of the New Subordinated
         Debt).

         2.13. Section Addition of Section 8.15. Section 8.15 shall be added to
the Agreement and shall read in its entirety as follows:

         Section 8.15. No More Restrictive Covenants. No Borrower will, nor will
         any Borrower permit Guarantor or any Subsidiary to, (a) enter into or
         permit to exist any loan agreement, credit agreement, purchase
         agreement or other agreement in connection with which Debt is or was
         incurred (a "Debt Agreement") which contains covenants, agreements or
         representations which are more restrictive than the covenants,
         agreements and representations which are contained in this Agreement
         and the Loan Documents, or (b) amend or modify any existing or future
         Debt Agreement in a manner which would result in such Debt Agreement,
         as amended or modified, containing covenants, agreements and
         representations which are more restrictive than the covenants,
         agreements and representations which are contained in this Agreement
         and the Loan Documents.

         2.14. Section Amendment to Article IX. Article IX contained in the
Agreement is amended to read in its entirety as follows:

                                   ARTICLE IX.

                               Financial Covenants

         Borrowers covenant and agree that, as long as the Obligations or any
         part thereof are outstanding or any Lender has any Commitment hereunder
         or Issuing Bank has any obligation to issue any Letter of Credit
         hereunder or any Letter of Credit Liabilities exist, Borrowers will
         observe and perform, and will cause Guarantor to observe and perform,
         the financial covenants set forth below, unless Agent and Majority
         Lenders shall otherwise consent in writing.


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<PAGE>

         Section 9.1. Current Ratio. Guarantor and its Subsidiaries will at all
         times maintain a Current Ratio of not less than (a) 0.90 to 1.00 for
         the fiscal quarters ending as of March 31, 2004 and June 30, 2004, (b)
         1.05 to 1.00 for the fiscal quarter ending as of September 30, 2004,
         and (c) 1.10 to 1.00 for the fiscal quarter ending as of December 31,
         2004. The Current Ratio shall be calculated and tested quarterly as of
         the last day of each fiscal quarter of Guarantor commencing with the
         fiscal quarter ending March 31, 2004.

         Section 9.2. Tangible Net Worth. Guarantor and its Subsidiaries will at
         all times maintain Tangible Net Worth in an amount not less than the
         sum of (a) $110,000,000.00, plus (b) seventy-five percent (75%) of Net
         Income for each fiscal quarter of Guarantor and its Subsidiaries which
         has been completed as of the date of calculation, commencing with the
         fiscal quarter ending March 31, 2004, provided, however, that in the
         event that Net Income of Guarantor and its Subsidiaries is not greater
         than zero for any fiscal quarter, an amount equal to zero shall be
         added to the calculation of Tangible Net Worth for such fiscal quarter,
         plus (c) ninety percent (90%) of the net proceeds of any common stock
         or other equity issued by Guarantor or any of its Subsidiaries after
         December 31, 2003. Tangible Net Worth shall be calculated and tested
         quarterly as of the last day of each fiscal quarter of Guarantor
         commencing with the fiscal quarter ending March 31, 2004. Any audit
         adjustment for the fiscal year ended December 31, 2003 that results in
         an adjustment to the equity accounts in an amount in excess of
         $53,416,000.00 will adjust the minimum Tangible Net Worth requirement
         on a dollar for dollar basis.

         Section 9.3. Fixed Charge Coverage Ratio. Guarantor and its
         Subsidiaries will maintain a Fixed Charge Coverage Ratio of not less
         than (a) 1.50 to 1.00 for the fiscal quarter ending as of September 30,
         2004 and (b) 1.40 to 1.00 for the fiscal quarter ending as of December
         31, 2004.

         Section 9.4. EBITDAR. Guarantor and its Subsidiaries will maintain
         EBITDAR of not less than (a) negative $2,500,000.00 for the three (3)
         months ended March 31, 2004, (b) negative $4,500,000.00 for the six (6)
         months ended June 30, 2004, (c) positive $8,000,000.00 for the nine (9)
         months ended September 30, 2004, and (d) positive $20,000,000.00 for
         the twelve (12) months ended December 31, 2004. The requirements
         contained in clauses (a) and (b) are to the effect that EBITDAR shall
         not be less than, or (otherwise stated) more negative than, the
         negative amounts required therein.

         Section 9.5. Capital Expenditures. Guarantor and its Subsidiaries will
         not incur Capital Expenditures in an aggregate amount (for Guarantor
         and its Subsidiaries) which exceeds $8,000,000.00; provided that Agent
         and Majority Lenders shall review specific requests by Guarantor and
         its Subsidiaries for additional project specific capital expenditures,
         during any calendar year.


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         2.15. Section Amendment to Section 10.1. Clauses (n) and (o) shall be
added to Section 10.1 of the Agreement and shall read in their entirety as
follows:

         (n) An Event of Default, as defined in the Purchase Agreement, shall
         occur.

         (o) Guarantor (or any Borrower or any Subsidiary) shall pay any
         principal, interest or fees on the New Subordinated Debt in cash,
         except for cash payments of principal of the New Subordinated Debt
         which are paid from (i) the proceeds of Pemex Contract EPC-64 or the
         Williams Contract, or (ii) the proceeds of the issuance of equity at
         any time after March 1, 2004.

         2.16. Section Amendment to Exhibits. Exhibit "I" to the Agreement (No
Default Certificate) is amended to conform in its entirety to Annex "A" to this
Amendment.


                                   3. ARTICLE

                              Conditions Precedent

         (a) Section Conditions. The effectiveness of this Amendment is subject
         to the receipt by Agent of the following, each in form and substance
         satisfactory to Agent and Lenders:

              (i)  Certificate-Each Borrower. A certificate of the Secretary or
                   another officer of each Borrower acceptable to Agent
                   certifying (A) resolutions of the board of directors of each
                   Borrower which authorize the execution, delivery and
                   performance by such Borrower of this Amendment and the other
                   Loan Documents to which such Borrower is or is to be a party,
                   and (B) the names of the officers of each Borrower authorized
                   to sign this Amendment and each of the other Loan Documents
                   to which such Borrower is or is to be a party together with
                   specimen signatures of such officers.

             (ii)  Fees. An extension fee payable to Agent for the Pro-Rata
                   benefit of Lenders in the amount of $100,000.00, and an Agent
                   fee payable to the Agent in the amount of $10,000.00.

            (iii)  Additional Information. Such additional documents,
                   instruments and information as Lenders or Agent may request.

         (b) The effectiveness of this Amendment is subject to the occurrence of
         the following events:

         (i) New Subordinated Debt Documents. Agent shall have reviewed the New
         Subordinated Debt and all promissory notes and other instruments and
         documents delivered in connection with the New Subordinated Debt, and
         all terms of the New Subordinated Debt and all such promissory notes
         and other instruments (including interest rate, payment terms to the
         effect that no cash


                                      -12-

<PAGE>

         payments may be made thereon, financial covenants and collateral)
         shall be acceptable to Agent.

         (ii) New Subordinated Debt Closing. The closing for the New
         Subordinated Debt shall have occurred or shall occur simultaneously
         with the closing of the transactions contemplated by this Amendment,
         and the New Subordinated Debt shall be an effective obligation of
         Guarantor or shall become an effective obligation of Guarantor
         simultaneously with the closing of the transactions contemplated by
         this Amendment.

         (iii) Approval of Other Debt. Agent and Majority Lenders shall have had
         the opportunity to review, and shall be satisfied with, any and all
         financial covenants to be contained in any documents evidencing or
         related to Debt of Guarantor or any Subsidiary (other than Debt
         evidenced by the Loan Documents or the Foreign Loan Agreement) and the
         documents executed in connection therewith.


                                   4. ARTICLE

                 Ratifications, Representations, and Warranties

         4.1. Section Ratifications. The terms and provisions set forth in this
Amendment shall modify and supersede all inconsistent terms and provisions set
forth in the Agreement and except as expressly modified and superseded by this
Amendment, the terms and provisions of the Agreement are ratified and confirmed
and shall continue in full force and effect. Borrowers and Lenders agree that
the Agreement as amended hereby shall continue to be the legal, valid and
binding obligation of such Persons enforceable against such Persons in
accordance with its terms.

         (a) Section Representations, Warranties and Agreements. Each Borrower
hereby represents and warrants to Lenders that the execution, delivery, and
performance of this Amendment and any and all other Loan Documents executed or
delivered in connection herewith have been authorized by all requisite action on
the part of such Borrower and will not violate the Organizational Documents of
such Borrower, the representations and warranties contained in the Agreement as
amended hereby, and all other Loan Documents are true and correct on and as of
the date hereof as though made on and as of the date hereof, no Event of Default
or Unmatured Event of Default has occurred and is continuing, Borrowers are in
full compliance with all covenants and agreements contained in the Agreement as
amended hereby, Borrowers are indebted to Lenders pursuant to the terms of the
Notes, as the same may have been renewed, modified, extended and rearranged, the
liens, security interests, encumbrances and assignments created and evidenced by
the Loan Documents are, respectively, valid and subsisting liens, security
interests, encumbrances and assignments and secure the Notes as the same may
have been renewed, modified or rearranged, and no Borrower has any claims,
credits, offsets, defenses or counterclaims arising from the Loan Documents or
any Lender's performance under the Loan Documents.


                                      -13-

<PAGE>

         4.2. Section Additional Representations. Each Borrower hereby
represents and warrants to Lenders that no Borrower or any Subsidiary is a party
to any loan agreement, credit agreement, purchase agreement or other agreement
in connection with which Debt was incurred which contains covenants, agreements
or representations which are more restrictive than the covenants, agreements and
representations which are contained in the Loan Agreement, as amended by this
Amendment, and the Loan Documents.


                                   5. ARTICLE

                                  Miscellaneous

         5.1. Section Survival of Representations and Warranties. All
representations and warranties made in this Amendment or any other Loan
Documents including any Loan Document furnished in connection with this
Amendment shall fully survive the execution and delivery of this Amendment and
the other Loan Documents, and no investigation by any Lender or any closing
shall affect the representations and warranties or the right of any Lender to
rely on them.

         5.2. Section Reference to Agreement. Each of the Loan Documents,
including the Agreement and any and all other agreements, documents, or
instruments now or hereafter executed and delivered pursuant to the terms hereof
or pursuant to the terms of the Agreement, as amended hereby, are hereby amended
so that any reference in such Loan Documents to the Agreement shall mean a
reference to the Agreement, as amended hereby.

         5.3. Section Expenses. As provided in the Agreement, Borrowers agree to
pay on demand all costs and expenses incurred by Agent in connection with the
preparation, negotiation and execution of this Amendment and the other documents
and instruments executed pursuant hereto and any and all amendments,
modifications and supplements thereto, including, without limitation, the costs
and fees of Agent's legal counsel, and all costs and expenses incurred by Agent
in connection with the enforcement or preservation of any rights under the
Agreement, as amended hereby, or any other Loan Document, including, without
limitation, the costs and fees of Agent's legal counsel.

         5.4. Section Severability. Any provision of this Amendment held by a
court of competent jurisdiction to be invalid or unenforceable shall not impair
or invalidate the remainder of this Amendment and the effect thereof shall be
confined to the provision so held to be invalid or unenforceable.

         5.5. SECTION APPLICABLE LAW. THIS AMENDMENT AND ALL OTHER LOAN
DOCUMENTS EXECUTED PURSUANT HERETO SHALL BE DEEMED TO HAVE BEEN MADE AND TO BE
PERFORMABLE IN HOUSTON, HARRIS COUNTY,


                                      -14-

<PAGE>

TEXAS AND SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE
STATE OF TEXAS.

         5.6. Section Successors and Assigns. This Amendment is binding upon and
shall inure to the benefit of Agent, Issuing Bank, each Lender and each Borrower
and their respective successors and assigns, except that no Borrower may assign
or transfer any of its rights or obligations hereunder without the prior written
consent of Agent.

         5.7. Section Counterparts. This Amendment may be executed in one or
more counterparts, each of which when so executed shall be deemed to be an
original, but all of which when taken together shall constitute one and the same
instrument.

         5.8. Section Effect of Waiver. No consent or waiver, express or
implied, by Agent, Issuing Bank or any Lender to or for any breach of or
deviation from any covenant, condition or duty by any Borrower shall be deemed a
consent or waiver to or of any other breach of the same or any other covenant,
condition or duty.

         5.9. Section Headings. The headings, captions, and arrangements used in
this Amendment are for convenience only and shall not affect the interpretation
of this Amendment.

         5.10. SECTION ECH CONFIRMATION OF GUARANTY. BY ITS EXECUTION OF THIS
AMENDMENT, ECH OFFSHORE, S. DE R.L. DE C.V. ("ECH") (A) RATIFIES AND CONFIRMS
THE GUARANTY AGREEMENT DATED AS OF MAY 30, 2002, EXECUTED BY ECH IN FAVOR OF
AGENT (THE "ECH GUARANTY"), AND (B) AGREES THAT, (I) THE ECH GUARANTY HAS NOT
BEEN RESCINDED, REVOKED OR TERMINATED, AND (II) THE ECH GUARANTY REMAINS IN FULL
FORCE AND EFFECT.

         5.11. SECTION WAIVER OF FAILURE TO COMPLY WITH FINANCIAL COVENANTS. BY
THEIR EXECUTION OF THIS AMENDMENT AGENT AND LENDERS WAIVE COMPLIANCE BY
BORROWERS AND GUARANTOR WITH THE PROVISIONS OF SECTIONS 9.1, 9.2, 9.3, 9.4, 9.5,
9.6 AND 9.7 FOR THE FISCAL YEAR ENDED DECEMBER 31, 2003, AND AGENT AND LENDERS
WAIVE ANY AND ALL EVENTS OF DEFAULT WHICH MAY ARISE UNDER THE AGREEMENT AS A
RESULT OF BORROWERS' AND GUARANTOR'S FAILURE TO COMPLY WITH SECTIONS 9.1, 9.2,
9.3, 9.4, 9.5, 9.6 AND 9.7 OF THE AGREEMENT FOR THE FISCAL YEAR ENDED DECEMBER
31, 2003. THE WAIVER CONTAINED IN THIS SECTION 6.10 IS EFFECTIVE AS OF DECEMBER
31, 2003, BUT DOES NOT CONSTITUTE A WAIVER OF ANY OTHER PROVISION OF, OR
REQUIREMENT OF THE AGREEMENT NOR DOES IT CONSTITUTE A WAIVER OF COMPLIANCE WITH
SECTIONS 9.1, 9.2, 9.3, 9.4, 9.5, 9.6 AND 9.7 AT ANY TIME AFTER DECEMBER 31,
2003. BY THEIR EXECUTION OF THIS AMENDMENT, AGENT AND LENDERS ALSO WAIVE ANY
EVENT OF DEFAULT WHICH MAY HAVE ARISEN AS A RESULT OF THE EXECUTION, DELIVERY
AND PERFORMANCE BY VESSELS OF THAT CERTAIN ASSIGNMENT OF CHARTER DATED JUNE 29,
2001 EXECUTED


                                      -15-

<PAGE>

BY VESSELS IN FAVOR OF GENERAL ELECTRIC CAPITAL CORPORATION AND THAT CERTAIN
ASSIGNMENT OF CHARTER HIRE DATED JUNE 4, 2003 EXECUTED BY VESSELS IN FAVOR OF
ELLIOTT ASSOCIATES, L.P.


                                      -16-

<PAGE>
         5.12. SECTION ENTIRE AGREEMENT. THIS AMENDMENT AND ALL OTHER
INSTRUMENTS, DOCUMENTS, AND AGREEMENTS EXECUTED AND DELIVERED IN CONNECTION WITH
THIS 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 AMENDMENT AND THE OTHER INSTRUMENTS, DOCUMENTS AND
AGREEMENTS EXECUTED AND DELIVERED IN CONNECTION WITH THIS 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.

         Executed as of the date first written above.


                                   BORROWERS:

                                   HORIZON OFFSHORE CONTRACTORS, INC.


                                   By:
                                       ----------------------------------------
                                       David W. Sharp
                                       Executive Vice President


                                   HORIZON SUBSEA SERVICES, INC.


                                   By:
                                       ----------------------------------------
                                       David W. Sharp
                                       Executive Vice President



                                   HORIZON VESSELS, INC.


                                   By:
                                       ----------------------------------------
                                       David W. Sharp
                                       Executive Vice President


                                      -17-

<PAGE>

                                   AGENT:

                                   SOUTHWEST BANK OF TEXAS, N.A., as Agent


                                   By:
                                       ----------------------------------------
                                       Valerie Gibbs
                                       Senior Vice President



                                    LENDERS:

                                    SOUTHWEST BANK OF TEXAS, N.A.


                                   By:
                                       ----------------------------------------
                                       Valerie Gibbs
                                       Senior Vice President



                                    DRESDNER BANK AG, NEW YORK AND
                                    GRAND CAYMAN BRANCHES


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


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



                                    BANK OF SCOTLAND


                                   By:
                                       ----------------------------------------
                                       Joseph Fratus
                                       First Vice President


                                      -18-

<PAGE>

                                    HIBERNIA NATIONAL BANK


                                   By:
                                       ----------------------------------------
                                       Tammy Boyd
                                       Vice President



                                                     COASTAL BANC SSB


                                   By:
                                       ----------------------------------------
                                       Ed Selke
                                       Chief Credit Officer




         The undersigned Guarantor (a) hereby consents and agrees to this
Amendment, (b) agrees that all references to the Loan Agreement contained in the
Guaranty Agreement-Guarantor executed by Guarantor shall constitute references
to such Loan Agreement as amended by the Amendment and as the same may be
further amended, and (c) agrees that the Guaranty Agreement-Guarantor executed
by Guarantor shall remain in full force and effect and shall continue to be the
legal, valid and binding obligations of Guarantor, enforceable against Guarantor
in accordance with its terms and shall evidence Guarantor's guaranty of the
Notes as renewed and extended from time to time.


                                   HORIZON OFFSHORE, INC.


                                   By:
                                       ----------------------------------------
                                       David W. Sharp
                                       Executive Vice President


                                      -19-

<PAGE>

         Each of the undersigned Additional Guarantors (a) hereby consents and
agrees to this Amendment, (b) agrees that all references to the Loan Agreement
contained in the Guaranty Agreement executed by such Additional Guarantor shall
constitute references to such Loan Agreement as amended by the Amendment and as
the same may be further amended, and (c) agrees that the Guaranty Agreement
executed by such Additional Guarantor shall remain in full force and effect and
shall continue to be the legal, valid and binding obligations of such Additional
Guarantor, enforceable against such Additional Guarantor in accordance with its
terms and shall evidence such Additional Guarantor's guaranty of the Notes as
renewed and extended from time to time.


                                   Additional Guarantors:
                                   ---------------------

                                   PROGRESSIVE PIPELINE CONTRACTORS, INC.
                                   AFFILIATED MARINE CONTRACTORS, INC.
                                   TEXAS OFFSHORE CONTRACTORS CORP.
                                   FLEET PIPELINE SERVICES, INC.
                                   GULF OFFSHORE CONSTRUCTION, INC.
                                   BAYOU MARINE CONTRACTORS, INC.


                                   By:
                                       ----------------------------------------
                                       David W. Sharp
                                       Executive Vice President


                                   HORIZON GROUP L.D.C.


                                   By:
                                       ----------------------------------------
                                       David W. Sharp
                                       Director


                                   HORIZON OFFSHORE NIGERIA LTD.


                                   By:
                                       ----------------------------------------
                                       David W. Sharp
                                       Director


                                      -20-

<PAGE>

                                   TIBURON INGENIERIA Y CONSTRUCCION, S. DE
                                   R.L. DE C.V.


                                   By:
                                       ----------------------------------------
                                       David W. Sharp
                                       Secretary


                                   HORIZON VESSELS INTERNATIONAL LTD.


                                   By:
                                       ----------------------------------------
                                       David W. Sharp
                                       Vice President


                                   PT HORIZON INDONESIA


                                   By:
                                       ----------------------------------------
                                       David W. Sharp
                                       Commissioner


                                   HORIZON OFFSHORE INTERNATIONAL LTD.


                                   By:
                                       ----------------------------------------
                                        David W. Sharp
                                        Executive Vice President


                                   HORIZON MARINE CONSTRUCTION LTD.


                                   By:
                                       ----------------------------------------
                                       David W. Sharp
                                       Executive Vice President


                                      -21-

<PAGE>

                                   HORIZON OFFSHORE PTE. LTD.


                                   By:
                                       ----------------------------------------
                                       David W. Sharp
                                       Director


                                   HORIZON OFFSHORE CONTRACTORS (MAURITIUS) LTD.


                                   By:
                                       ----------------------------------------
                                       David W. Sharp
                                       Director


                                   HORIZON MARINE CONSTRUCTION (MAURITIUS) LTD.


                                   By:
                                       ----------------------------------------
                                       David W. Sharp
                                       Director


                                   HORIZON C-BAY COSTA AFUERA, S. DE
                                   R.L. DE C.V.


                                   By:
                                       ----------------------------------------
                                       David W. Sharp
                                       Member


                                   HOC OFFSHORE, S. DE R.L. DE C.V.


                                   By:
                                       ----------------------------------------
                                       David W. Sharp
                                       Director


                                      -22-

<PAGE>

                                   PT ARMANDI PRANAUPAYA


                                   By:
                                       ----------------------------------------
                                       David W. Sharp
                                       Director


                                   ECH OFFSHORE, S. DE R.L. DE C.V.


                                    By:
                                       ----------------------------------------
                                       Bill J. Lam
                                       Sole Manager


                                   HORIZON MARINE CONTRACTORS (MALAYSIA) SDN BHD


                                   By:
                                       ----------------------------------------
                                       David W. Sharp
                                       Director


                                   HORIZON OFFSHORE SERVICES, LTD.


                                   By:
                                       ----------------------------------------
                                       David W. Sharp
                                       Executive Vice President and
                                       Chief Financial Officer


                                   MARINE LEASING (LABUAN) PTE LTD


                                   By:
                                       ----------------------------------------
                                       David W. Sharp
                                       Executive Vice President and
                                       Chief Financial Officer


                                      -23-

<PAGE>
                                 LIST OF ANNEXES


         Annex                                     Document

             A                               No Default Certificate


                                      -24-