EXHIBIT 10.20

      AMENDMENT NO. 4

                                       TO

                                 LOAN AGREEMENT

      AMENDMENT NO. 4 ("Amendment No. 4") dated as of January 31, 2000 (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 "Guarantor"), THE CIT GROUP/EQUIPMENT FINANCING, INC., a New York
corporation ("CIT"), HELLER FINANCIAL LEASING, INC., a Delaware corporation,
U.S. BANCORP LEASING & FINANCIAL, an Oregon corporation, SAFECO CREDIT
COMPANY, INC. ("Safeco"), a Washington corporation, TRANSAMERICA EQUIPMENT
FINANCIAL SERVICE CORPORATION, a Delaware corporation, PHOENIXCOR, INC., a
Delaware corporation, and DEUTSCHE FINANCIAL SERVICES CORPORATION, a Nevada
corporation (collectively, the "Original Lenders") and CIT as Agent for the
Original Lenders (the "Agent").

      W I T N E S S E T H:
      - - - - - - - - - -

      WHEREAS, pursuant to the Loan Agreement, the Original Lenders made
available to the Borrowers a loan facility of up to USD 83,300,000, as evidenced
by the amended and restated secured promissory note of the Borrowers dated
November 30, 1999; and

      WHEREAS, the Borrowers have requested that certain covenants of the Loan
Agreement be amended as set forth herein; and

      WHEREAS, Safeco wishes to purchase a portion of CIT's portion of the
Commitment equal to USD 3,300,000; and

      WHEREAS, the Guarantor wishes to incorporate a new subsidiary, Horizon
Subsea Services, Inc., a Delaware corporation (the "New Subsidiary"); and

      WHEREAS, the parties wish to amend the Loan Agreement to reflect the
foregoing and to amend certain provisions 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)   Each reference in the Loan Agreement to "Amendment
      Documents" is hereby amended to include the Amendment Documents listed
      in Section 4.1 of this Amendment No. 4.
      2.    Section 3.3(o) of the Loan Agreement is hereby amended to read as
follows:
<PAGE>
      (o)   FIXED CHARGE COVERAGE RATIO.  Permit their Fixed Charge Coverage
            Ratio to be less than:

            (i)   1.10 to 1 at December 31, 1999;

            (ii)  1.05 to 1 at March 31, 2000; and

            (iii) .90 to 1 at June 30, 2000;

            (iv)  1.05 to 1 at September 30, 2000; and

            (v)   1.50 to 1 at December 31, 2000 and at any time thereafter; for
                  the twelve (12) month period ending immediately prior to the
                  relevant date of determination.

      3.    Schedule 1 to the Loan Agreement is hereby replaced with Schedule
1 attached to this Amendment No. 4.

      4.    CONDITIONS PRECEDENT.


      4.1 DOCUMENTS REQUIRED AS CONDITIONS PRECEDENT TO AMENDMENT NO. 4. The
effectiveness of the modifications to the Loan Agreement contemplated by this
Amendment No. 4 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 (the "Amendment Documents")
      shall have been duly authorized and executed with original counterparts
      thereof delivered to the Agent:

                  (i)   This Amendment No. 4;

                  (ii)  Amendment No. 4 to the United States First Preferred
                        Fleet Mortgage;

                  (iii) Amendment No. 4 to Vanuatu First Preferred Fleet
                        Mortgage; and

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


            (b) In consideration of Amendment No. 4 to this Agreement and in
      consideration of the Lenders' agreement to (i) amend the financial
      covenants in accordance with Amendment No. 4 to this Agreement and (ii)
      not require an increase in

EXHIBIT 10.20

                                       2
<PAGE>
      the Fixed Rate or the margin applicable to the LIBOR Rate as consideration
      for such amendment to the financial covenants amended hereby, Borrowers
      shall pay to the Agent, for the ratable benefit of the Lenders, an
      amendment fee ("Amendment Fee") of $188,718 and the Lenders hereby consent
      to such payment. Payment by the Borrowers of the Amendment Fee and the
      Lenders' acceptance thereof shall in no event prejudice the ability of the
      Lenders to increase the Fixed Rate or the margin applicable to the LIBOR
      Rate pursuant to (X) the terms of the Loan Agreement, (Y) any future
      amendment of any Loan Document or (Z) any waivers or consents requested of
      the Lenders or the Agent under any Loan Document by the Borrowers.

            (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.

      4.2 WAIVER OF CONDITIONS PRECEDENT. All of the conditions precedent
contained in this Section 4 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.

      5.    REPRESENTATIONS OF THE BORROWERS AND GUARANTOR.  The Borrowers
and the Guarantor represent and warrant that:

            (a) Each of the Borrowers and the Guarantor 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 Guarantor of the Amendment Documents and any other instrument or
      agreement provided for by this Amendment No. 4 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. 4) 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 Guarantor 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


EXHIBIT 10.20

                                       3
<PAGE>
      Guarantor is a party. The enforceability of this Amendment No. 4, 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 Guarantor 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.
      4 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.

      6. EXPENSES. The Borrowers and the Guarantor agree to promptly, whether or
not the modifications to the Loan Agreement contemplated by this Amendment No. 4
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. 4 and all other documents referred
to herein, and all amendments or waivers to or termination of this Amendment No.
4 or any agreement referred to herein; and (y) reimburse the Agent for all fees
and disbursements of 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. 4 and all other documents referred to herein, whether
by judicial proceedings or otherwise. The obligations of the Borrowers and the
Guarantor under this Section 6 shall survive payment of the Loan.

      7. 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. 4.

      8.    Except as specifically amended by this Amendment No. 4, all of
the terms and provisions of the Loan Agreement shall remain in full force and
effect.

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

      10.   THIS AMENDMENT NO. 4 TO LOAN AGREEMENT SHALL BE GOVERNED BY AND
CONSTRUED IN ACCORDANCE WITH THE INTERNAL LAWS OF THE STATE
OF NEW YORK.

EXHIBIT 10.20

                                       4
<PAGE>
EXHIBIT 10.20

                                       5
<PAGE>
      IN WITNESS WHEREOF, the parties hereto have duly executed this Amendment
No. 4 to Loan Agreement on the date first written above.

                                    BORROWERS:

                                    HORIZON OFFSHORE CONTRACTORS, INC.


                                    By:____
                                    Name:__
                                    Title:_

                                    HORIZON VESSELS, INC.


                                    By:____
                                    Name:__
                                    Title:_

                                    GUARANTOR:

                                    HORIZON OFFSHORE, INC.


                                    By:____
                                    Name:__
                                    Title:_

                                    LENDERS:

                                    THE CIT GROUP/EQUIPMENT FINANCING, INC.


                                    By:____
                                    Name:__
                                    Title:_

                                    SAFECO CREDIT COMPANY, INC.


                                    By:____
                                    Name:__
                                    Title:_

EXHIBIT 10.20

                                       6
<PAGE>

EXHIBIT 10.20

                                       7
<PAGE>
                                    U.S. BANCORP LEASING & FINANCIAL


                                    By:____
                                    Name:__
                                    Title:_

                                    HELLER FINANCIAL LEASING, INC.


                                    By:____
                                    Name:__
                                    Title:_

                                    TRANSAMERICA EQUIPMENT FINANCIAL SERVICE
                                    CORPORATION

                                    By:____
                                    Name:__
                                    Title:_

                                    PHOENIXCOR, INC.


                                    By:____
                                    Name:__
                                    Title:_

                                    DEUTSCHE FINANCIAL SERVICES CORPORATION


                                    By:____
                                    Name:__
                                    Title:_

                                    AGENT:

                                    THE CIT GROUP/EQUIPMENT FINANCING, INC.


                                    By:____

EXHIBIT 10.20

                                       8
<PAGE>
                                    Name:__
                                    Title:_

      SCHEDULE 1 TO

                        AMENDMENT NO. 4 TO LOAN AGREEMENT

      LENDER                        PORTION OF COMMITMENT

1.    The CIT Group/Equipment
      Financing, Inc.               USD   20,000,000

2.    Heller Financial
      Leasing, Inc.                 USD   15,000,000

3.    TransAmerica Equipment
      Financial Service Corp.       USD   15,000,000

4.    U. S. Bancorp Leasing
      & Financial                   USD   10,000,000

5.    Safeco Credit Company,
      Inc.                          USD   8,300,000

6.    Phoenixcor, Inc.              USD   5,000,000

7.    Deutsche Financial Services
      Corporation                   USD   10,000,000


EXHIBIT 10.20

                                        9