Abstract: Hydrocarbon liquids and/or gases are recovered from thick underground deposits of oil-bearing limestone or dolomite by drilling two or more boreholes from the earth's surface into the lower part of the deposit, establishing communication between the boreholes, burning the oil in said limestone or dolomite in an area between the boreholes to decompose the alkaline earth carbonate into alkaline earth oxide, flushing out the alkaline earth oxide formed by the combustion with water to form a cavity, collapsing the overlying oil-bearing limestone or dolomite into the cavity to form a rubblized zone extending vertically to a point near the upper boundary of the deposit, driving a flame front vertically through the rubblized zone to liberate hydrocarbon liquids and produce gases, and recovering the liquids and/or gases from the rubblized zone.

Abstract: Coal liquids and gases are recovered from a thick underground coal seam by drilling one or more boreholes from the earth's surface into the lower part of the seam, burning out the coal over a limited area near the bottom of the seam, collapsing the overlying coal to form a rubblized zone extending vertically to a point near the upper boundary of the seam, driving a flame front vertically through the rubblized zone to liberate hydrocarbon liquids and produce gases, and recovering the liquids and gases from the rubblized zone.