A reform ending windfalls for concessionaires in national parks seems certain this fall. Only minor differences remain between House and Senate bills that passed overwhelmingly. Both bills mandate competition for contracts of more than $500,000, require that concession fees return to parks, and establish a briefer duration on contracts. The current law, passed in 1965, was based on the perceived need to lure businesses into parks that were seen as remote and difficult places to make a profit. But the Washington, D.C.-based National Parks and Conservation Association, which has lobbied for years to change the law, says concessionaires reap huge profits thanks to their monopoly status. Reform would also end a practice that made concessionaires permanent owners of improvements instead of leaseholders. When the Park Service decided to terminate its contract with General Host in Yellowstone National Park in the late 1970s, for example, it had to pay $19 million to acquire buildings. While negotiations went on, says NPCA staffer Phil Vorhees, service to the public deteriorated. One glitch in the compromise negotiations: The Arizona group, Grand Canyon River Guides, opposes competition for all contracts. "Intuitively, competition is great," says past guides president Tom Moody. "But in our case it could drive out small companies and destabilize our industry."