Since the Superfund program began in 1980, the Environmental Protection Agency (EPA) has spent about $17.7 billion to clean up hazardous waste sites. EPA oversees the work, but private contractors do the actual cleanups--known as remedial actions--of Superfund sites. GAO has issued a series of reports that describe the portion of EPA's funds spent on remedial actions by contractors, as opposed to other activities, such as studying conditions at sites, designing cleanup remedies, and travel. (See GAO/RCED-97-211, Sept. 1997, GAO/RCED-98-221, Aug. 1998, and GAO/RCED-99-139, May 1999.) This report examines the costs at the following five Superfund sites: the Raymark site in Stratford, Connecticut; the Sharon Steel site in Midvale, Utah; the United Creosoting site in Conroe, Texas; the NL Industries site in Granite City, Illinois; and the Newmark site in San Bernadino, California. For each site, GAO discusses (1) what portion of the total funds EPA spent on each site was used to pay contractors for remedial actions as opposed to other activities and how the contractors spent the money and (2) whether the actual costs for remedial actions differed from the estimated costs and why.