Huff and puff process for retorting oil shale

Greater product yield and quality as well as simplified gas recovery can be attained by a huff and puff process for retorting oil shale. The process can be advantageously carried out in in situ retorts under ground as well as in surface retorts above ground. In the process, an active retort of raw oil shale is retorted without prior combustion of oil shale therein with retort off gases, which have been heated in a spent shale retort. In the preferred mode, retort off gases from the active retort and air are alternately injected into the spent retort to cyclically heat the off gases and combust the coked shale. The retort off gases can be deoiled and optionally scrubbed of carbon dioxide and hydrogen sulfide before being heated in the spent retort.