EXHIBIT A --------- Agreement of Joint Filing ------------------------- The undersigned hereby agree that they are filing jointly pursuant to Rule 13d-1 of the Securities Exchange Act of 1934 the statement dated April 10, 1997, containing the...

 
                                   EXHIBIT A
                                   ---------

                           Agreement of Joint Filing
                           -------------------------


          The undersigned hereby agree that they are filing jointly pursuant to
Rule 13d-1 of the Securities Exchange Act of 1934 the statement dated April 10,
1997, containing the information required by Schedule 13D, for the 14,092,482
Shares of the Common Stock of Tosco Corporation held by Union Oil Company of
California.

Dated April 10, 1997
                                       UNOCAL CORPORATION
                                       UNION OIL COMPANY OF
                                       CALIFORNIA

 
                                       By: /s/ Xxxxxx X. Xxxxxxxxxxx
                                           Xxxxxx X. Xxxxxxxxxxx
                                           Vice President, Tax