Oil shale leasing : hearing before the Subcommittee on Minerals, Materials, and Fuels of the Committee on Interior and Insular Affairs, United States Senate, Ninety-fourth Congress, second session, on S. 2413, a bill to amend section 21 of the Mineral Leasing Act (41 STAT. 445), as amended (30 U.S.C. 241), March 17, 1976. (U.S. Govt. Print. Off, 1976)