Pursuant to a congressional request, GAO provided information on certain aspects of the Department of Defense's (DOD) environmental compliance and cleanup activities, focusing on the: (1) extent to which DOD components are meeting requirements to provide data on the cost and status of compliance projects; and (2) relative risk characteristics DOD uses to determine priorities for site cleanup. GAO noted that: (1) not all the information that DOD, the Environmental Protection Agency (EPA), and Congress have identified as required for compliance oversight is being provided; (2) DOD components do not provide detailed expenditure data on compliance activities; (3) DOD's reports to EPA do not provide such information as whether compliance projects address existing or expected noncompliance; (4) in addition, some data in DOD's latest report to Congress were not complete or correct; (5) DOD used a relative risk site evaluation methodology in designating 4,472 of 8,534 sites as high-risk; (6) GAO's analysis of reported data on 407 high-cost sites, including 266 considered high risk, indicates that DOD includes a range of site characteristics within its high-risk category; (7) at 54 percent of the sites that were designated as high-risk, all three elements used by DOD to make priority determinations were reported present; (8) at the remaining 46 percent of the sites one or two of the elements, but not all three, were reported present; and (9) in addition, the reported levels of contamination at 58 of the 407 sites GAO analyzed were less than the standard DOD used to determine whether a site is contaminated.