Summary: Pursuant to a congressional request, GAO reviewed the cost-sharing agreement between a contractor and the Army to study and clean up contamination at the Rocky Mountain Arsenal, and the cost data for the contractor's lease of Army facilities for commercial operations. GAO noted that: (1) the Army and the contractor formalized their cost-sharing arrangement that delineates the cleanup process, financial and accounting procedures, and cleanup responsibilities; (2) as of December 1995, Army costs totalled $308 million, contractor costs totalled $95 million, and commingled costs totalled $656 million; (3) the Army agreed to pay 50 percent of commingled costs up to $700 million and 80 percent of costs exceeding $700 million; (4) as of June 3, 1996, commingled costs had not exceeded $700 million; (5) the lease for the Army facilities began in 1947 with a predecessor contractor and ended in 1987; and (6) the annual base lease payment was $36,000 in 1947, increased to $238,000 by 1965, and decreased to $146,000 by 1987.