This work presents a review of investigations concerning formation of thermobitumen (TB) and a systematic experimental study of thermobituminization of Baltic oil shale, Kukersite, in autoclaves. The bituminizing process was performed at different nominal temperatures (340-380 degrees C) and residence times (20 min-10 hours). Distribution of organic matter of the shale between thermobitumen, gas and insoluble in benzene solid residue was studied. Composition of thermobitumen depending on pyrolysis conditions was characterized. The pyrolysis process of kukersite in autoclaves consists of three stages: 1. Formation of TB and gas from kerogen until obtaining the maximum yield of TB. 2. Equilibrium of formation and thermal cleavage of TB molecules. The yield of TB is maximum and practically constant in this stage. The quantity of gas grows continously and that of organic solid residue is minimal. The lower is the temperature, the longer is the thermobituminization stage. 3. Destruction of obtained TB forming gas, coke and oil. The formed oil favors extraction of TB from solid residue, but a part of kerogen gets lost with coke. The duration of these stages depends oil the nominal temperature being shorter at higher temperatures.