Abstract: A low cost, high efficiency process for treating oil shale is provided which allows essentially complete recovery of the valuable hydrocarbon fraction of the shale, including light ends, without direct firing of the shale or use of other expensive processing steps heretofore proposed. In preferred forms, the oil shale is heated in a closed heating system using circulating, oxygen-free gases until the shale "break point," or temperature at which the hydrocarbons begin to vaporize from the shale, is reached; at this point the system is slowly depressurized and hydrocarbons are simultaneously released to a condensation stage for the recovery thereof and control of circulating fan horsepower. Steam may also be added to the circulating system to further purge hydrocarbons from the shale and provide additional control of fan horsepower.