GAO reviewed the types of contracts, source selection evaluation criteria, and work statements that the Department of Defense (DOD) uses to award large multi-function or "umbrella" contracts for base support services to determine whether its contracting practices adhere to law, regulation, and policy. GAO found that: (1) although most of the work was of a predictable nature, contracting officers often decided to use umbrella contracts, even though they were not the most advantageous method of meeting the government's needs; (2) contracting officers neither followed preferred practices in awarding umbrella contracts nor justified decisions to use umbrella contracts based on less-preferred contracting practices, rather than two or more smaller contracts; (3) significant portions of the routine base support work performed under cost reimbursement and fixed-price incentive contracts appeared suitable for firmer types of contracts; (4) the services awarded most umbrella contracts based on technical, rather than price, competition; and (5) DOD regulations did not require existing umbrella contract work statements to follow the concepts in the Office of Management and Budget (OMB) work statement guidance.