A non-subsidence method for developing an in situ oil shale retort tract in a subterranean formation containing oil shale includes forming a number of spaced apart rows of in situ oil shale retorts, leaving intervening zones of unfragmented formation between adjacent rows of retorts for supporting the...http://www.google.com/patents/US4368921?utm_source=gb-gplus-sharePatent US4368921 - Non-subsidence method for developing an in situ oil shale retort
