Pursuant to a congressional request, GAO reviewed the basis for the North Atlantic Trade Organization's (NATO) cost estimate for enlarging its membership.

GAO noted that: (1) the approach used by NATO in determining its estimated direct enlargement cost of $1.5 billion for commonly funded requirements is reasonable; (2) GAO found that NATO's assessment was based on site visits, historic data, and extensive dialogue with invitee officials; (3) a key assumption of the NATO cost estimate is that the current low threat environment will continue for the foreseeable future; (4) any changes in the threat environment could affect enlargement-related military requirements and costs; (5) based on GAO's work at NATO and its prior analysis of enlargement estimates, GAO concludes that the Department of Defense's (DOD) assessment of the NATO cost report was reasonable; (6) according to DOD, the U.S. Joint Staff validated the requirements on which these costs were based as militarily sound; and (7) morever, DOD emphasized that the NATO study was a more accurate reflection of commonly funded costs than DOD's 1997 study.