Exhibit 99.1

                                   CERTIFICATE
                                 furnished under
                  Section 906 of the Sarbanes-Oxley Act of 2002

     I, Gary L.  Rainwater,  chief  executive  officer of CILCORP  Inc.,  hereby
certify that to the best of my  knowledge,  the  accompanying  Report of CILCORP
Inc. on Form 10-Q for the quarter ended March 31, 2003,  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 CILCORP Inc.



                                                /s/ Gary L. Rainwater
                                                ----------------------------
                                                    Gary L. Rainwater
                                                       President
                                               (Principal Executive Officer)


Date: May 15, 2003

A signed  original of this  written  statement  required by Section 906 has been
provided to CILCORP Inc.  and will be retained by CILCORP Inc. and  furnished to
the Securities and Exchange Commission or its staff upon request.