Abstract: Kerogen and other combustible matter can be extracted from an area of oil shale or tarsand by drilling boreholes in a selected pattern through the overlying soil and rock without removing it. Each borehole mouth is tightly closed by a cover provided with an air inlet pipe and a gas exhaust pipe. In the covers of one or several boreholes, the inlet pipe is centrally guided and longitudinally movable in an upward and downward direction, and a laser beam generated by a laser source is inroduced into the upper end of the pipe and directed centrally to its bottom where it is diverted toward the borehole wall by a mirror assembly. The laser beam moved along the borehole wall irradiates the oil shale or tarsand and ignites the combustible matter contained therein which liquefies and evaporates. Combustion spreads from the initially ignited bore to the remaining bores in the area through the fissures in the formation and likewise serves to liquefy and evaporate the kerogen there.