Summary: As of March 1996, the Defense Department (DOD) had set aside $3.4 billion for environmental cleanup at bases being closed under the base realignment and closure process. However, as more bases are closed and more cleanup efforts are undertaken, program costs are likely to rise significantly. Available DOD data suggest that program costs are likely to exceed $11 billion. The key reasons for the high cost of closing base cleanups are (1) the large number of contaminated sites and difficulties arising from the types of contamination, (2) requirements of federal and state laws and regulations, (3) lack of cost-effective cleanup technology for some contaminants, and (4) intended property reuse. Options for reducing cleanup costs at closing bases include deferring or extending cleanup actions, modifying existing laws and regulations, adopting more-effective cleanup technologies, and sharing costs with the ultimate user of the property. All of these options, however, have the potential for adversely impacting the goals of the program.