Hardness, tensile strength, and impact toughness of dry and brine- saturated sandstone specimens were measured at ambient, cryogenic, and elevated temperatures as a measure of the relative stability of reservoir rocks for subsurface disposal of liquid wastes. Hardness measurements were inconclusive. Tensile strength and impact toughness were significantly higher at -320 deg f than at ambient temperature, but were relatively unaffected at 700 deg f. Impact toughness was reduced by subjecting the specimens to three cycles of rapid temperature changes (thermal shock) over a 1,000 deg f range. Tensile strength of brine-saturated sandstone was less than that of dry sandstone. Based on results of the tests, reservoir sandstone likely would be stable if exposed to extreme temperatures of liquid wastes, although rapid changes in waste temperatures should be avoided.