Structural response and/or deformation was determined for each of four different grade Green River oil shales (27.0-, 34.5-, 45.5-, and 63.5-Gal/ton) as they were heated in an inert atmosphere, under constant compressive stress, from ambient to subretorting temperatures; that is, below those required for rapid pyrolysis of the organic matter. Small cores and small columns of confined fragments comprised the test specimens, which were heated in a specially designed microunit at a uniform rate either to 725 deg or to 825 deg f under three different stress levels, 80, 200, and 325 psi. Structural response of some cores was observed as they were heated in a stress-free environment. The obtained stress-strain- time-temperature relationships provide information regarding the oil shale's yield temperature, yield stress, rate of compressive strain, loss of mechanical strength, and nature of structural deformation. Effects of structural deformation on induced permeability in small columns of fragments are presented. Results indicate that underground retorting of Green River oil shale may be seriously impaired through loss of induced permeability brought about by structural deformation of rich oil shale under the influence of heat and compressive stress.