Oil shales, liptobioliths, and hard coals were subjected to sub- and supercritical water extraction in an autoclave. Thermosolvolytical potential of water on the yield and composition of conversion products at 573-673 K was investigated. The effects of the exchanging of a part of water by the same amount of some low-boiling hydrocarbon or CO2 and of the addition of chemically active reagents to extraction were also investigated. Depending upon the experimental conditions and the origin of organic matter, different yields of conversion products were obtained. On extraction with binary solvents, an synergistic effect of solvents was observed with respect to extract yield, the value of that effect being directed not only on the structure of organic matter but also on temperature, reaction time, solvent type, and the concentration ratio of substitute to water. When the labile compounds were added to water, the incorporation of their fragments into coals and shales structure was detected. The extracts were characterized by large content of heteroatomic and high-polar compounds.