The company continued its efforts in oil shale extraction until May 2, 1982, when Exxon (which had bought Atlantic Richfield's 60% share in the project in 1980) pulled out of the Colony Project joint venture, leaving Tosco unable to keep the venture viable in spite of a $1.1 million loan guarantee from the U.S. government.

Several takeover bids during the 1980s failed to materialize, and another major reorganization took place in 1991 with the company moving its headquarters to Stamford, Connecticut.

In 1997, Tosco bought the rights to the Union 76 brand of gas stations and the western United States refining and marketing operations from Unocal.

The San Francisco Chronicle reported[6] that one Tosco employee, Anthony Creggett, claimed shortly after the fire that plant managers had refused a request by four workers to shut down the high-temperature distillation tower during the repairs on the pipe.

In spring 2001, local gas prices spiked after a fire at a Tosco plant in Carson, California, south of Los Angeles, that released toxic smoke visible 90 miles away.