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Exhibit 10.3

THIRD AMENDMENT TO EXIM GUARANTEED LOAN AGREEMENT

        THIS THIRD AMENDMENT TO EXIM GUARANTEED LOAN AGREEMENT (this
"Amendment"), dated as of September 30, 2002, is between HORIZON OFFSHORE
CONTRACTORS, INC., a Delaware corporation ("Contractors"), HORIZON SUBSEA
SERVICES, INC., a Delaware corporation ("Subsea"), HORIZON VESSELS, INC., a
Delaware corporation ("Vessels"), and HORIZEN, L.L.C., a Delaware limited
liability company ("LLC", and together with Contractors, Subsea and Vessels 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 and Lenders entered into that certain EXIM Guaranteed
Loan Agreement dated as of August 15, 2001, as amended by First Amendment to
EXIM Guaranteed Loan Agreement dated as of April 17, 2002 and Second Amendment
to EXIM Guaranteed Loan Agreement dated as of August 28, 2002 (the "Agreement").

        B.    Pursuant to the Agreement, each Borrower, Horizon Offshore, Inc.,
a Delaware corporation, and Horizon Offshore Contractors, Ltd., a company
organized and existing under the laws of the Cayman Islands, each executed a
Guaranty dated as of August 15, 2001, and ECH Offshore, S. de R.L. de C.V., a
company organized and existing under the laws of Mexico, executed a Guaranty
dated as of August 15, 2001 (under Mexican law) and a Guaranty dated as of
May 30, 2002 (under Texas law), pursuant to which such Persons (as defined in
the Agreement) guaranteed to Agent the payment and performance of the
Obligations (as defined in the Agreement).

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

        D.    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:

ARTICLE I.

Definitions

        Section I.1.    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.

ARTICLE II.

Amendments

        Section II.1.    Amendment to Certain Definitions.    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:

            "Domestic Loan Agreement" means that certain Loan Agreement dated
March 26, 2001, among Borrowers other than LLC, the Domestic Agent and the
lenders referred to therein, as amended by First Amendment to Loan Agreement
dated April 17, 2002, Second Amendment to Loan Agreement dated May 30, 2002,
Third Amendment to Loan Agreement dated as of

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August 28, 2002, and Fourth Amendment to Loan Agreement dated as of
September 30, 2002, 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.

            "Loan Authorization Agreement" means the Second Amended and Restated
Loan Authorization Agreement dated October 15, 2002, between Eximbank and
Lender, and all amendments thereto and all restatements and replacements
thereof, and the Loan Authorization Agreement shall constitute a Loan Document.

        Section II.2.    Amendment to Section 9.6.    Section 9.6 of the
Agreement shall be amended to read in its entirety as follows.

        Section 9.6.    Ratio of Funded Debt to EBITDA.    Parent and its
Subsidiaries will at all times maintain a Ratio of Funded Debt to EBITDA of not
greater than (a) 3.85 to 1.00 for the quarter ended September 30, 2002, and
(b) 3.50 to 1.00 for the quarter ending December 31, 2002 and at all times
thereafter. The Ratio of Funded Debt to EBITDA will be calculated and tested
quarterly as of the last day of each fiscal quarter of Parent, and for purposes
of calculating the Ratio of Funded Debt to EBITDA, EBITDA shall be calculated
for the period of four fiscal quarters ended as of the date of calculation.
Notwithstanding the foregoing, if the Vessel Purchase Event occurs, the Ratio of
Funded Debt to EBITDA shall be not greater than 3.90 to 1.00 for the fiscal
quarter of Parent ending December 31, 2002; provided, however, that for the
fiscal quarter of Parent ending December 31, 2002, in calculating the Ratio of
Funded Debt to EBITDA, an amount equal to fifty percent (50%) of the acquisition
cost of the new vessel shall be subtracted from Funded Debt in the numerator;
provided, further, that as of the end of all other fiscal quarters of Parent,
the Ratio of Funded Debt to EBITDA shall be not greater than 3.50 to 1.00 as
provided in clause (b) of the first sentence of this Section 9.6; and provided,
further, that, except for the change in the Ratio of Funded Debt to EBITDA
described in this sentence at the times described in this section, this sentence
does not constitute an amendment or waiver of any provision of this Agreement.

        Section II.3.    Amendment to Schedules and Exhibits.    Exhibit "V" to
the Agreement (No Default Certificate) is amended to conform in its entirety to
Annex "A" to this Amendment.

ARTICLE III.

Conditions Precedent

        Section III.1.    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:

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

        (b)    Certificate—LLC.    A certificate of a Manager or another officer
of LLC acceptable to Agent certifying (i) resolutions of the Members of LLC
which authorize the execution, delivery and performance by LLC of this Amendment
and the other Loan Documents to which LLC is or is to be a party, and (ii) the
names of the Managers or other officers of LLC

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authorized to sign this Amendment and each of the other Loan Documents to which
LLC is or is to be a party together with specimen signatures of such Persons.

        (c)    Amendment Fee.    An amendment fee in the amount of $12,000.00.

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

ARTICLE IV.

Ratifications, Representations, and Warranties

        Section IV.1.    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.

        Section IV.2.    Representations, Warranties and Agreements.    Each
Borrower hereby represents and warrants to Lenders that (a) 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, (b) 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, (c) upon the effectiveness of this Amendment no Event
of Default or Unmatured Event of Default will exist, (d) upon the effectiveness
of this Amendment Borrowers will be in full compliance with all covenants and
agreements contained in the Agreement as amended hereby, (e) Borrowers are
indebted to Lenders pursuant to the terms of the Notes, as the same may have
been renewed, modified, extended and rearranged, (f) 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 (g) no Borrower has any claims, credits,
offsets, defenses or counterclaims arising from the Loan Documents or any
Lender's performance under the Loan Documents.

ARTICLE V.

Miscellaneous

        Section V.1.    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.

        Section V.2.    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.

        Section V.3.    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

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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.

        Section V.4.    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.

        Section V.5.    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, TEXAS AND SHALL BE GOVERNED BY AND
CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF TEXAS.

        Section V.6.    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.

        Section V.7.    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.

        Section V.8.    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.

        Section V.9.    Headings.    The headings, captions, and arrangements
used in this Amendment are for convenience only and shall not affect the
interpretation of this Amendment.

        Section V.10.    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.

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        Executed as of the date first written above.

    BORROWERS:
 
 
HORIZON OFFSHORE CONTRACTORS, INC.
 
 
By:

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David W. Sharp
Executive Vice President
 
 
HORIZEN, L.L.C.
 
 
By:

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R. Clay Etheridge
President
 
 
HORIZON SUBSEA SERVICES, INC.
 
 
By:

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David W. Sharp
Executive Vice President
 
 
HORIZON VESSELS, INC.
 
 
By:

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David W. Sharp
Executive Vice President
 
 
AGENT:
 
 
SOUTHWEST BANK OF TEXAS, N.A., as Agent
 
 
By:

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Valerie Gibbs
Senior Vice President
 
 
LENDERS:
 
 
SOUTHWEST BANK OF TEXAS, N.A.
 
 
By:

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Valerie Gibbs
Senior Vice President

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DRESDNER BANK LATEINAMERIKA AG
 
 
By:

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Alan Hills
Vice President
 
 
By:

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Sergio Goloubeff
First Vice President
 
 
BANK OF SCOTLAND
 
 
By:

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Joseph Fratus
Vice President
 
 
HIBERNIA NATIONAL BANK
 
 
By:

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Gary Culbertson
Vice President

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

    HORIZON OFFSHORE, INC.
 
 
By:

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David W. Sharp
Executive Vice President
 
 
HORIZON OFFSHORE CONTRACTORS, LTD.
 
 
By:

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David W. Sharp
Director
 
 
ECH OFFSHORE, S. DE R.L. DE C.V.
 
 
By:

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R. Clay Etheridge
Sole Manager

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Other 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:

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David W. Sharp
Executive Vice President
 
 
HORIZON GROUP L.D.C.
 
 
By:

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David W. Sharp
Director
 
 
HORIZON OFFSHORE NIGERIA LTD.
 
 
By:

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David W. Sharp
Director
 
 
TIBURON INGENIERIA Y CONSTRUCCION, S.
DE R.L. DE C.V.
 
 
By:

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David W. Sharp
Secretary
 
 
HORIZON VESSELS INTERNATIONAL LTD.
 
 
By:

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David W. Sharp
Vice President
 
 
PT HORIZON INDONESIA
 
 
By:

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David W. Sharp
Commissioner
 
 
HORIZON OFFSHORE INTERNATIONAL LTD.
 
 
By:

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David W. Sharp
Executive Vice President

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HORIZON MARINE CONSTRUCTION LTD.
 
 
By:

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David W. Sharp
Executive Vice President
 
 
HORIZON OFFSHORE PTE. LTD.
 
 
By:

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David W. Sharp
Director
 
 
HORIZON OFFSHORE CONTRACTORS
(MAURITIUS) LTD.
 
 
By:

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David W. Sharp
Director
 
 
HORIZON MARINE CONSTRUCTION
(MAURITIUS) LTD.
 
 
By:

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David W. Sharp
Director
 
 
HORIZON C-BAY COSTA AFUERA, S.
DE R.L. DE C.V.
 
 
By:

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David W. Sharp
Member
 
 
HOC OFFSHORE, S. DE R.L. DE C.V.
 
 
By:

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R. Clay Etheridge
President
 
 
PT ARMANDI PRANAUPAYA
 
 
By:

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David W. Sharp
Director

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LIST OF ANNEXES

Annex

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  Document

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A   No Default Certificate

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ANNEX "A"

No Default Certificate

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QuickLinks

Exhibit 10.3

THIRD AMENDMENT TO EXIM GUARANTEED LOAN AGREEMENT
RECITALS
ARTICLE I. Definitions
ARTICLE II. Amendments
ARTICLE III. Conditions Precedent
ARTICLE IV. Ratifications, Representations, and Warranties
ARTICLE V. Miscellaneous
LIST OF ANNEXES
ANNEX "A" No Default Certificate