<PAGE>

                                                                   Exhibit 10.48

                                 AMENDMENT NO. 9

                                       TO

                                 LOAN AGREEMENT

     AMENDMENT NO. 9 ("Amendment No. 9", and together with the documents listed
in Section 10 hereof, the "Amendment Documents") dated as of March __, 2004 (the
"Amendment Date") to the Loan Agreement dated as of December 30, 1998, as
amended (the "Loan Agreement"), among HORIZON VESSELS, INC., a Delaware
corporation, HORIZON OFFSHORE CONTRACTORS, INC., a Delaware corporation
(together, the "Borrowers"), HORIZON OFFSHORE, INC., a Delaware corporation (the
"Parent Guarantor"), THE CIT GROUP/EQUIPMENT FINANCING, INC., a New York
corporation ("CIT"), HELLER FINANCIAL LEASING, INC., a Delaware corporation,
U.S. BANCORP EQUIPMENT FINANCE, INC., formerly known as U.S. BANCORP LEASING &
FINANCIAL, an Oregon corporation, SAFECO CREDIT COMPANY, INC., a Washington
corporation, TRANSAMERICA EQUIPMENT FINANCIAL SERVICE CORPORATION, a Delaware
corporation, PHOENIXCOR, INC., a Delaware corporation, and LASALLE NATIONAL
LEASING CORPORATION, a ______________ corporation (collectively, the "Lenders")
and CIT as Agent for the Lenders (the "Agent").

                                   WITNESSETH:

     WHEREAS, pursuant to the Loan Agreement, the Lenders made available to the
Borrowers a loan facility of up to USD 91,397,845; and

     WHEREAS, the parties wish to amend the Loan Agreement to amend certain
covenants thereof.

     NOW THEREFORE, in consideration of the above recitals and for other good
and valuable consideration, the receipt and sufficiency of which is hereby
acknowledged, the parties agree to amend the Loan Agreement as follows:

     1. The Definitions of the Loan Agreement are hereby amended as follows:

          (a) A definition of "Capital Lease" is hereby added to the Loan
     Agreement and reads as follows:

          "Capital Lease" means a lease of any property by the Parent Guarantor
          or any of its subsidiaries as lessee that is, or should be in
          accordance with GAAP (including Financial Accounting Standards Board
          Statement No. 13, as amended or superseded from time to time),
          recorded as a 'capital lease' on the balance sheet of the Parent
          Guarantor or its subsidiaries prepared in accordance with GAAP."

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          (b) A definition of "Cash Interest" is hereby added and reads as
     follows:

          "Cash Interest" means the cash portion of Interest Expense.

          (c) The definition of "Current Liabilities" is hereby amended to read
     as follows:

          "Current Liabilities" means Indebtedness of the Parent Guarantor which
          would in accordance with GAAP be classified on a consolidated basis as
          current liabilities of a corporation conducting a business the same as
          or similar to the business of the Borrowers and the Parent Guarantor,
          excluding the principal amount outstanding under any revolving credit
          facility of the Parent Guarantor or its subsidiaries and any balloon
          payment due in the next twelve (12) months."

          (d) A definition of "Current Maturities of Long Term Debt" is hereby
     added to the Loan Agreement and reads as follows:

          "Current Maturities of Long Term Debt" means for the Parent 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 the Parent Guarantor and its subsidiaries, excluding
          the principal amount due under any revolving credit facility of the
          Parent Guarantor or its subsidiaries and any balloon payment due in
          the next twelve (12) months."

          (e) The definition of "EBITDA" is hereby amended to read as follows:

          "EBITDA" means for the Parent 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."

          (f) The definition of "EBITDAR" is hereby added to the Loan Agreement
     and reads as follows:

          "EBITDAR" means for the Parent 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 the
          Borrowers (for the professional advisors to the Borrowers, the Lenders
          or other creditors) not to exceed $1,600,000 for the fiscal year ended
          December 31, 2004.


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          (g) The definition of "Fixed Charge Coverage Ratio" is hereby amended
     to read as follows:

          "Fixed Charge Coverage Ratio" means for the Parent 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 September 30, 2004, plus (C) Tax Expense for the
          quarter ended as of September 30, 2004, (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 September 30, 2004 and
          December 31, 2004, plus (C) Tax Expense for the quarters ended as of
          September 30, 2004 and December 31, 2004, (c) as of March 31, 2005,
          (i) EBITDA for the quarters ended September 30, 2004, December 31,
          2004, and March 31, 2005 divided by (ii) the sum of (A) Current
          Maturities of Long Term Debt as of March 31, 2005 times .75
          (seventy-five percent), plus (B) Cash Interest for the quarters ended
          September 30, 2004, December 31, 2004, and March 31, 2005, plus (C)
          Tax Expense for the quarters ended September 30, 2004 , December 31,
          2004, and March 31, 2005, and (d) for all quarters ending thereafter,
          (i) EBITDA for the four (4) quarters then ended divided by (ii) the
          sum of (A) Current Maturities of Long Term Debt as of the quarter then
          ended, plus (B) Cash Interest for the four (4) quarters then ended,
          plus (C) Tax Expense for the four (4) quarters then ended.

          (h) A definition of "Net Income" is hereby added to the Loan Agreement
     and reads as follows:

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

          (i) The definition of "Net Worth" is hereby deleted and replaced with
     the following:

          "Tangible Net Worth" means, at any particular date, all amounts which,
          in conformity with GAAP, would be included as stockholder's equity on
          a consolidated balance sheet of the Parent Guarantor and its
          subsidiaries; provided, however, there shall be excluded from Tangible
          Net Worth (a) any amount at which shares of capital stock of the
          Parent Guarantor or any of its subsidiaries appear as an asset on the
          Parent Guarantor's or subsidiary's balance sheet, (b) goodwill,
          including any amounts, however


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          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 the Parent Guarantor or any of its subsidiaries or any Affiliate,
          (f) all other assets which are properly classified as intangible
          assets, and (g) paid-in-kind interest on the 2004 Subordinated Notes."

          (j) A definition of "Tax Expense" is hereby added to the Loan
     Agreement and reads as follows:

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

          (k) A definition of "Total Funded Debt" is hereby added to the Loan
     Agreement and reads as follows:

          "Total Funded Debt" means, as of any date of determination, without
          duplication, the sum of (a) all principal Indebtedness of the Parent
          Guarantor and its subsidiaries for borrowed money on that date (other
          than intercompany Indebtedness), plus (b) the aggregate amount of all
          monetary obligations of the Parent Guarantor and its subsidiaries
          under any and all Capital Leases on such date."

          (l) A definition of "2004 Subordinated Notes" is hereby added to the
     Loan Agreement and reads as follows:

          "2004 Subordinated Notes" means the 16% Subordinated Secured Notes due
          March 31, 2007 of Horizon Offshore, Inc., issued pursuant to the
          Purchase Agreement dated as of March __, 2004, together with any
          additional notes in respect of accrued interest, and all related liens
          and security documents.

     2. Section 1.6(a)(ii) of the Loan Agreement is hereby amended to add the
following sentence:

          "Notwithstanding the terms of this Section 1.6(a)(ii), the Borrowers
          shall not be required to prepay the Loan pursuant to this Section
          1.6(a)(ii) during the period from the date of Amendment No. 9 through
          May 10, 2005."

     3. Section 3.3(m) of the Loan Agreement is hereby amended by adding the
following provision:

          "The Parent Guarantor shall not permit its Current Ratio to be less
          than 0.90 to 1 for the period ending March 31, 2004, 0.90 to 1 for the
          period


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          ending June 30, 2004, 1.05 to 1 for the period ending September 30,
          2004, 1.10 to 1 for the period ending December 31, 2004, and 1.10 to 1
          for the period ending March 31, 2005 and each period thereafter."

     4. Section 3.3(o) of the Loan Agreement is hereby amended to read as
follows:

          "The Parent Guarantor shall not permit its Fixed Charge Coverage Ratio
          to be less than 1.50 to 1 for the three-month period ending September
          30, 2004, 1.40 to 1 for the six-month period ending December 31, 2004,
          1.33 to 1 for the nine-month period ending March 31, 2005, and 1.33 to
          1 for each period thereafter on a rolling four quarter basis."

     5. Section 3.3(q) of the Loan Agreement is hereby amended to read as
follows:

          "The Parent Guarantor 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
          the Parent 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 the Parent 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 the Parent Guarantor or any of its subsidiaries after
          December 31, 2003. The calculation will exclude the cumulative effect
          of the paid in kind interest related to the 2004 Subordinated Notes
          for purposes of both this Section 3.3(q) and the definition of
          Tangible Net Worth. Tangible Net Worth shall be calculated and tested
          quarterly as of the last day of each fiscal quarter of the Parent
          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 hereof on a dollar for dollar basis."

     6. A new Section 3.3(bb) is hereby added to the Loan Agreement and reads as
follows:

          "(bb) EBITDAR. Permit their EBITDAR to be less than USD -2,500,000 for
          the three-month period ending March 31, 2004, USD -4,500,000 for the
          six-month period ending June 30, 2004, USD 8,000,000 for the
          nine-month period ending September 30, 2004, and USD 20,000,000 for
          the twelve-month period ending December 31, 2004. For the three-month
          period ending March 31, 2005, the Parent Guarantor will maintain a
          positive EBITDAR."


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     7. A new Section 3.3(cc) is hereby added to the Loan Agreement and reads as
follows:

          "(cc) 2004 Subordinated Notes. Prior to (1) the maturity of the 2004
          Subordinated Notes, repay or prepay the 2004 Subordinated Notes,
          except from the proceeds of collateral securing such 2004 Subordinated
          Notes, or by way of conversion thereof into common stock of Horizon
          Offshore, Inc. or by the issuance of additional securities of Horizon
          Offshore, Inc., subject to the provisions hereof, and (2) the
          repayment in full of the Loan, make any cash payment of interest on
          the 2004 Subordinated Notes, except from the proceeds of collateral
          securing such 2004 Subordinated Notes, or by way of conversion thereof
          into common stock of Horizon Offshore, Inc. or by the issuance of
          additional securities of Horizon Offshore, Inc., subject to the
          provisions hereof. If the Loan Agreement is still in effect at the
          time of the maturity of the 2004 Subordinated Notes, the 2004
          Subordinated Notes may be repaid upon the maturity thereof only if no
          Default or Event of Default has occurred and is continuing. The
          Borrowers and the Parent Guarantor shall not amend the terms of the
          2004 Subordinated Notes to (1) shorten the maturity thereof, (2)
          increase the interest rate payable thereunder or (3) provide
          additional security therefor, without the prior written consent of the
          Majority Lenders."

     8. All references in the Loan Documents to the "Loan Agreement" shall
hereafter refer to the Loan Agreement as amended by this Amendment No. 9.

     9. Conditions Precedent.

          9.1 Documents Required as Conditions Precedent to Amendment No. 9. The
effectiveness of the modifications to the Loan Agreement contemplated by this
Amendment No. 9 is subject to the condition precedent that the Agent shall have
received at or prior to the Amendment Date all of the following, each dated on
or before the Amendment Date and each in form and substance satisfactory to the
Agent and its counsel:

          (a) Each of the following documents and other items shall have been
     duly authorized and executed with original counterparts thereof delivered
     to the Agent:

               (i) This Amendment No. 9;

               (ii) Evidence sufficient to the Agent that the indebtedness under
          the 2004 Subordinated Notes is subordinated to the Loan in form and
          substance satisfactory to the Agent;

               (iii) Evidence sufficient to the Agent that the Borrowers and the
          Parent Guarantor have received proceeds from the 2004 Subordinated
          Notes of no less than USD 45,000,000 and have refinanced approximately


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<PAGE>

          USD 15,000,000 in existing subordinated indebtedness with the
          remainder of the proceeds of the 2004 Subordinated Notes;

               (iv) Copies of all relevant documentation respecting the issuance
          of the 2004 Subordinated Notes, including without limitation any
          offering circulars, note purchase agreements, security agreements and
          notes;

               (v) Copies of all original financing documents relating to the
          Borrowers' and Guarantors' loan facility with Southwest Bank of Texas,
          N.A., including without limitation any amendments; and

               (vi) such further documents as the Lenders may reasonably
          request.

          (b) The Borrowers shall have paid a fee to the Agent for ratable
     distribution to the Lenders on or before the date hereof equal to 1.35% of
     the outstanding amount of the Loan.

          (c) The representations and warranties contained in Section 3.1 of the
     Loan Agreement shall be true on the Amendment Date with the same effect as
     though such representations and warranties had been made on and as of such
     date, and no Event of Default specified in Article IV of the Loan Agreement
     and no event which, with the lapse of time or the giving of notice and the
     lapse of time specified in Article IV of the Loan Agreement, would become
     such an Event of Default, shall have occurred and be continuing.

          9.2 Conditions Subsequent. The Borrowers shall, within ten (10) days
following the date of this Amendment No. 9, provide each of the following to the
Agent:

               (i) Ratification of Guaranty executed by the Guarantors;

               (ii) Second Preferred Ship Mortgages on certain vessels owned by
          the Borrowers; and

               (iii) An opinion of counsel to the Borrowers and the Parent
          Guarantor respecting the due authorization, execution and delivery of
          this Amendment No. 9 and related documents and the issuance of the
          2004 Subordinated Notes.

          9.3 Waiver of Conditions. All of the conditions contained in this
Section 9 are for the sole benefit of the Agent and the Lenders and the Agent
may waive any of them in its absolute discretion, and on such conditions as it
deems proper.

     10. Representations of the Borrowers and Guarantors. The Borrowers and the
Guarantors represent and warrant that:


                                       7

<PAGE>

          (a) Each of the Borrowers and the Guarantors is a corporation, duly
     organized and validly existing in good standing under the laws of the State
     of Delaware, and has the requisite power and authority (i) to carry on its
     business as presently conducted; and (ii) to enter into and perform its
     obligations under the Amendment Documents.

          (b) The execution, delivery and performance by each of the Borrowers
     and the Guarantors of the Amendment Documents and any other instrument or
     agreement provided for by this Amendment No. 9 to which it is a party, have
     been duly authorized by all necessary corporate action, do not require
     stockholder approval other than such as has been duly obtained or given, do
     not or will not contravene any of the terms of its Certificate of
     Incorporation or Bylaws, and will not violate any provision of law or of
     any order of any court or governmental agency or constitute (with or
     without notice or lapse of time or both) a default under, or result (except
     as contemplated by this Amendment No. 9) in the creation of any security
     interests, lien, charge or encumbrance upon any of its properties or assets
     pursuant to, any agreement, indenture or other instrument to which it is a
     party or by which it may be bound other than is in favor of the Agent; the
     Amendment Documents have been duly executed and delivered by the Borrowers
     and the Guarantors and constitute the respective legal, valid and binding
     agreements, enforceable in accordance with the respective terms thereof as
     to which each of the Borrowers and the Guarantors is a party. The
     enforceability of this Amendment No. 9, however, is subject to all
     applicable bankruptcy, insolvency, reorganization, moratorium, and other
     laws affecting the rights or creditors and to general equity principles.

          (c) Except as set forth in the Loan Agreement, there are no suits or
     proceedings pending or to its knowledge threatened against or affecting any
     Borrower or Guarantors which if adversely determined would have a material
     adverse effect upon its business, financial condition or operations.

          (d) Other than such as have been obtained, no license, consent or
     approval of any Governmental Agency or other regulatory authority is
     required for the execution, delivery or performance of this Amendment No. 9
     or any other Amendment Document or any instrument contemplated herein or
     therein. The Borrowers are the holder of all certificates and
     authorizations of governmental authorities required by law to enable it to
     engage in the business transacted by them.

     11. Expenses. The Borrowers and the Guarantors agree to promptly, whether
or not the modifications to the Loan Agreement contemplated by this Amendment
No. 9 become effective, (x) reimburse the Agent for all fees and disbursements
of external counsel to the Agent and all reasonable out of pocket fees and
disbursements of the Agent incurred in connection with the preparation,
execution and delivery of this Amendment No. 9 and all other documents referred
to herein, and all amendments or waivers to or termination of this Amendment No.
9 or any agreement referred to herein; and (y) reimburse the Agent for all fees
and disbursements of


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<PAGE>

internal and external counsel to the Agent and all reasonable out of pocket
fees, disbursements and travel-related expenses of the Agent incurred in
connection with the protection of the rights of the Agent under this Amendment
No. 9 and all other documents referred to herein, whether by judicial
proceedings or otherwise. The obligations of the Borrowers and the Guarantors
under this Section 11 shall survive payment of the Loan.

     12. Waiver and Amendment.

          (a) The Lenders hereby consent to the issuance by the Parent Guarantor
     of the 2004 Subordinated Notes, the incurrence by the Parent Guarantor of
     the indebtedness evidenced thereby, the guaranties by the Borrowers and
     certain other subsidiaries of the Parent Guarantor of the indebtedness
     evidenced thereby, and the grant of liens by the Borrowers and certain
     other subsidiaries of the Parent Guarantor securing the 2004 Subordinated
     Notes as set forth in the documentation therefor as of the date of this
     Amendment No. 9. This provision shall not be construed as a waiver of any
     other provision of the Credit Agreement, nor shall this provision be
     construed as precedent for any future request by the Borrowers or any
     Guarantor for a waiver of any provision of the Credit Agreement.

          (b) The Lenders hereby waive the failure of the Borrowers and the
     Parent Guarantor to meet the requirements of Sections 3.3(m), 3.3(o) and
     3.3(q) of the Loan Agreement for the period ending December 31, 2003. This
     waiver is granted for the period ending on December 31, 2003 only, and
     shall not be construed as a waiver of the provisions of such Sections of
     the Loan Agreement for any other period, nor shall this provision be
     construed as a waiver of any other provision of the Loan Agreement, nor
     shall this provision be construed as precedent for any future request by
     the Borrowers or any Guarantor for a waiver of any provision of the Loan
     Agreement.

          (c) Wherever and in each such place the term "Loan Agreement" is used
     throughout the Loan Agreement, such term shall be read to mean the Loan
     Agreement as amended by this Amendment No. 9.

          (d) Except as specifically amended by this Amendment No. 9, all of the
     terms and provisions of the Loan Agreement shall remain in full force and
     effect.

     13. Capitalized Terms. All capitalized terms used herein but not defined
herein shall have the meanings given to them in the Loan Agreement.

     14. GOVERNING LAW. THIS AMENDMENT NO. 9 TO LOAN AGREEMENT SHALL BE GOVERNED
BY AND CONSTRUED IN ACCORDANCE WITH THE INTERNAL LAWS OF THE STATE OF NEW YORK.


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     IN WITNESS WHEREOF, the parties hereto have duly executed this Amendment
No. 9 to Loan Agreement on the date first written above.

                                    BORROWERS:

                                    HORIZON OFFSHORE CONTRACTORS, INC.

                                    By:           /s/ David W. Sharp
                                       -----------------------------------------
                                       Name:          David W. Sharp
                                       Title: Executive Vice President and Chief
                                                    Financial Officer

                                    HORIZON VESSELS, INC.

                                    By:           /s/ David W. Sharp
                                       -----------------------------------------
                                       Name:          David W. Sharp
                                       Title: Executive Vice President and Chief
                                                    Financial Officer

                                    GUARANTORS:

                                    HORIZON OFFSHORE, INC.

                                    By:           /s/ David W. Sharp
                                       -----------------------------------------
                                       Name:          David W. Sharp
                                       Title: Executive Vice President and Chief
                                                    Financial Officer

                                    HORIZON SUBSEA SERVICES, INC.

                                    By:           /s/ David W. Sharp
                                       -----------------------------------------
                                       Name:          David W. Sharp
                                       Title: Executive Vice President and Chief
                                                    Financial Officer

<PAGE>

                                    AFFILIATED MARINE CONTRACTORS, INC.

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

                                    PROGRESSIVE PIPELINE CONTRACTORS, INC.

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

                                    TEXAS OFFSHORE CONTRACTORS CORP.

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

                                    LENDERS:

                                    THE CIT GROUP/EQUIPMENT FINANCING, INC.,
                                    SAFECO CREDIT COMPANY, INC., U.S. BANCORP
                                    EQUIPMENT FINANCE, INC., HELLER FINANCIAL
                                    LEASING, INC., TRANSAMERICA EQUIPMENT
                                    FINANCIAL SERVICE CORPORATION, PHOENIXCOR,
                                    INC., LASALLE NATIONAL LEASING CORPORATION,

                                    By: THE CIT GROUP/EQUIPMENT
                                        FINANCING, INC., as Agent

                                    By:          /s/ Charles T. Lee
                                       -----------------------------------------
                                    Name:          Charles T. Lee
                                    Title:      Senior Vice President

                                    THE CIT GROUP/EQUIPMENT FINANCING,
                                       INC., as Agent

                                    By:          /s/ Charles T. Lee
                                       -----------------------------------------
                                    Name:          Charles T. Lee
                                    Title:      Senior Vice President