PROSPECTUS SUPPLEMENT NO. 15

                                                Filed Pursuant to Rule 424(b)(3)
                                                Registration Nos. 333-86212
                                                                  333-86212-01

                                  $175,000,000

                                GATX Corporation

                     7.5% Convertible Senior Notes due 2007
                     Fully and Unconditionally Guaranteed by
                           GATX Financial Corporation

                                       and

                             Shares of Common Stock
                  issuable upon conversion of the Senior Notes

         This prospectus supplement supplements the prospectus dated June 19,
2002 of GATX Corporation and GATX Financial Corporation, as supplemented by
prospectus supplement no. 1 dated June 26, 2002, prospectus supplement no. 2
dated July 3, 2002, prospectus supplement no. 3 dated July 23, 2002, prospectus
supplement no. 4 dated August 9, 2002, prospectus supplement no. 5 dated August
29, 2002, prospectus supplement no. 6 dated September 12, 2002, prospectus
supplement no. 7 dated September 24, 2002, prospectus supplement no. 8 dated
October 3, 2002, prospectus supplement no. 9 dated October 9, 2002, prospectus
supplement no. 10 dated October 18, 2002, prospectus supplement no. 11 dated
October 31, 2002, prospectus supplement no. 12 dated November 18, 2002,
prospectus supplement 13 dated December 16, 2002 and prospectus supplement no.
14 dated January 2, 2003, relating to the sale by certain holders of our 7.5%
convertible senior notes due 2007 and the shares of our common stock issuable
upon conversion of the notes. You should read this prospectus supplement in
conjunction with the prospectus as supplemented to date. This prospectus
supplement is qualified by reference to the prospectus as so supplemented except
to the extent that the information in this prospectus supplement supersedes the
information contained in the prospectus as so supplemented. Capitalized terms
used in this prospectus supplement and not otherwise defined herein have the
meanings specified in the prospectus.

         The table of Selling Holders contained in the prospectus is hereby
amended to add the entity named below as a Selling Holder:

                                Principal Amount of
                                 Notes Beneficially            Number of Shares
                                     Owned That                 of Common Stock
     Name of Selling Holder          May be Sold               That May be Sold

Sage Capital                           $100,000                       2,933


         Investing in the notes and our common stock involves risks. See "Risk
Factors" beginning on page 5 of the prospectus.

         Neither the Securities and Exchange Commission nor any state securities
commission has approved or disapproved of these securities or passed upon the
accuracy or adequacy of this prospectus. Any representation to the contrary is a
criminal offense.

            The date of this prospectus supplement is March 25, 2003