Improvements in the selective extraction of relatively low molecular weight oils from coal, coal liquids, oil shales, shale oils, oil sands, heavy and semi-heavy oils, bitumens, and the like are provided by a continuous process involving contacting the material to be treated with supercritical water in a continuous operation at pressures of from 500 psi to 3000 psi, temperatures of 250° C. to 450° C., and in-reactor dwell times generally in excess of 25 seconds and up to 10 minutes.