Structural response and/or deformation of three rich oil shales to heat and compressive stress was determined. Specimens consisted of small cores and of small columns of fragments from oil shales assaying 34.5, 45.5, and 63.5 Gallons of oil per ton. Effect of structural deformation on induced permeability in the fragmented specimens was determined. Stress-strain-time-temperature relationships of these oil shales provided information regarding their yield temperature, yield stress, rate of compressive strain, and loss of mechanical strength as they were heated from ambient to sub-retorting temperatures--that is, below those required for rapid pyrolysis of the organic matter to produce oil. Structural response of some cores was also observed as they were heated in a stress-free environment. Results provide guidelines to assess and evaluate some problems that may be associated with recovery of shale oil by underground retorting methods.