In the pyrolysis process, oil shale is heated until its kerogen decomposes into vapors of a petroleum-like condensable shale oil, non-condensable combustible oil shale gas, and spent shale—a solid residue.
The ratio of oil shale gas to shale oil depends on retorting temperature and as a rule, increases by the rise of temperature.
Typical components of oil shale gas are usually methane, hydrogen, carbon monoxide, carbon dioxide, nitrogen, and different hydrocarbons like ethylene.
[3] Since 1948, Estonian-produced oil shale gas was used in Leningrad and the cities in North Estonia.
[8] As oil shale gas often occurs as a byproduct of shale oil extraction, depending on the processing technology, it may be used for heating the pyrolysis process.