SUPPLEMENTAL AGREEMENT OF AMERISTAR CASINOS, INC.

Exhibit 99.1

SUPPLEMENTAL AGREEMENT OF AMERISTAR CASINOS, INC.

Ameristar Casinos, Inc. (“ACI”) hereby agrees to furnish supplementally to the Securities and Exchange Commission upon request a copy of all omitted exhibits to the Credit Agreement, dated as of April 14, 2011, filed as Exhibit 4.2 to ACI's Annual Report on Form 10-K for the year ended December 31, 2011.

Dated as of February 28, 2012 AMERISTAR CASINOS, INC.

By: /s/ Xxxxx X. Xxxxx _

Xxxxx X. Xxxxx

Senior Vice President and General Counsel