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                                                                    EXHIBIT 99.1


                SUPPLEMENTAL AGREEMENT OF AMERISTAR CASINOS, INC.

Ameristar Casinos, Inc. ("ACI") hereby agrees to furnish supplementally to the
Securities and Exchange Commission a copy of all omitted exhibits and schedules
to the following agreements:

1.  Credit Agreement dated as of December 20, 2000 among ACI, the Lenders party
    thereto from time to time, Wells Fargo Bank, N.A., as Co-Arranger and
    Syndication Agent, Bear Stearns Corporate Lending Inc., as Documentation
    Agent, Deutsche Bank Securities Inc., as Lead Arranger and Sole Book
    Manager, and Bankers Trust Company, as Administrative Agent;

2.  Senior Subordinated Credit Agreement dated as of December 20, 2000 by and
    among ACI, the Guarantors named on the signature pages thereto, the Lenders
    named on the signature pages thereto, Bankers Trust Company, as Agent for
    the Lenders, and Bear Stearns Corporate Lending Inc., as Documentation Agent
    for the Lenders; and

3.  Indenture dated as of February 2, 2001 among ACI, the Guarantors (as defined
    therein) and U.S. Bank Trust National Association, as trustee.