FILED PURSUANT TO RULE 424(B)(3)
                                                     REGISTRATION NO. 333-110451
                                                                   333-110451-01

PROSPECTUS SUPPLEMENT NO. 4


                                  $125,000,000

                                GATX CORPORATION

                      5% SENIOR CONVERTIBLE NOTES DUE 2023
                     FULLY AND UNCONDITIONALLY GUARANTEED BY

                           GATX FINANCIAL CORPORATION

                           AND SHARES OF COMMON STOCK
                      ISSUABLE UPON CONVERSION OF THE NOTES

         This prospectus supplement supplements the prospectus dated January 20,
2004 of GATX Corporation and GATX Financial Corporation, as supplemented by
prospectus supplement No. 1 dated January 30, 2004, prospectus supplement No. 2
dated March 15, 2004 and prospectus supplement no. 3 dated April 16, 2004,
relating to the sale by certain holders of our 5% Senior Convertible Notes due
2023 and the shares of our common stock issuable upon conversion of the notes.
You should read this prospectus supplement in conjunction with the prospectus.
This prospectus supplement is qualified by reference to the prospectus except to
the extent that the information in this prospectus supplement supersedes the
information contained in the prospectus. Capitalized terms used in this
prospectus supplement and not otherwise defined herein have the meanings
specified in the prospectus.


         The following line item in the table of Selling Holders contained in
the prospectus is hereby amended as follows:




                                                  PRINCIPAL AMOUNT OF
                                                  NOTES BENEFICIALLY      NUMBER OF SHARES
                                                      OWNED THAT          OF COMMON STOCK
NAME OF SELLING HOLDER                                MAY BE SOLD         THAT MAY BE SOLD
- ----------------------                            -------------------     ----------------
                                                                    
DBAG London......................................     $ 14,463,000           610,472
Victory Capital Management as Agent for the
Victory Convertible Fund.........................     $    300,000            12,662



         INVESTING IN THE NOTES AND OUR COMMON STOCK INVOLVES RISKS. SEE "RISK
FACTORS" BEGINNING ON PAGE 5 OF THE PROSPECTUS.

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         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 June 2, 2004