WASHINGTON (Bloomberg) — A 79-year prohibition on oil-shale development in Wyoming and Utah is being lifted by the U.S. Interior Department.

In Federal Register notices scheduled for publication Thursday, the Interior Department's Bureau of Land Management said it will open 6 million acres in Wyoming and 1.7 million in Utah to leasing, pending analysis to determine if the land warrants special protections. The plan would take effect next month.

Companies such as Exxon-Mobil Corp., Royal Dutch Shell Plc and Chevron Corp. are studying production through a process that involves heating rock to extract oil. Western states may hold as much as 800 billion barrels of oil, which might be enough to fuel the U.S. for a century.

Congress last year lifted a ban on drafting a rule that would allow the leasing of the resource.