Exhibit 99.3 CERTIFICATE furnished under Section 906 of the Sarbanes-Oxley Act of 2002. I, Warner L. Baxter, chief financial officer of Ameren Corporation, hereby certify that to the best of my knowledge, the accompanying Report of Ameren Corporation on Form 10-K for the fiscal year ended December 31, 2002 fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934 and that information contained in such Report fairly presents, in all material respects, the financial condition and results of operations of Ameren Corporation. /s/ Warner L. Baxter ------------------------------ Warner L. Baxter Chief Financial Officer Date: March 31, 2003 A signed original of this written statement required by Section 906 has been provided to Ameren Corporation and will be retained by Ameren Corporation and furnished to the Securities and Exchange Commission or its staff upon request.