The objective of he program was to assess the potential environmental hazard posed by the surface disposal of raw and spent eastern oil shales. Three shales: Sunbury. Cleveland, and New Albany were investigated. The spent materials were derived in the case of the Sunbury shale from the Battelle, in the case of the Cleveland shale from the Rockwell. and in the case of the New Albany shale from the Hytort process. The raw, low carbonate Sunbury and Cleveland shales were found to produce acid drainage readily on exposure to the atmosphere and water; this action was accelerated by iron oxidizing bacteria. The raw New Albany shale behaved in a manner analogous to highly calcareous coals. No pyrite appeared to be left in the spent shales; the presence of ferrous sulfide in the New Albany and Cleveland shales was indicated . Mechanisms responsible for the results obtained are discussed.