Pursuant to a congressional request, GAO reviewed the Environmental Protection Agency's (EPA) Superfund cleanup efforts, focusing on comparing EPA's estimate of future cleanup times compared with the program's historical performance. GAO noted that: (1) as of July 1, 1997, remedial action had been completed at 13 percent (95) of the 752 sites placed on the National Priorities List in fiscal years 1986 through 1994; (2) these remedial actions were completed in an average of 6.3 years after the sites were listed; (3) as of the same date, remedial action had not been completed at 87 percent (657) of the sites listed in fiscal years 1986 through 1994; (4) these uncompleted sites had been in the cleanup process an average of 8.1 years, that is, they had been listed on the National Priorities List an average of 8.1 years earlier; (5) assuming that all remedial actions at these "in process" sites had been completed on July 1, 1997, the average cleanup duration for all sites listed on the National Priorities List during the 9-year period would have been 7.9 years, almost as long as EPA's 8-year estimate of the cleanup time for recently listed sites; (6) because such a larger proportion of the sites listed in the 9-year period are still in process, the average cleanup time for these sites will exceed 8 years, possibly by a substantial margin; and (7) furthermore, for EPA to meet its 8-year estimate for cleaning up recently listed sites will require much faster cleanup times than the program has produced in the past.