Abstract: There is described a method of recovering energy and/or combustible gas by thermally gasifying fuel during its partial combustion, wherein the fuel and an oxygen-containing gas are delivered to a reactor (1) and caused to circulate in a closed circuit of reactants and reaction products during partial combustion of the fuel. Circulation is effected by virtue of the fact that the reactor (1) is configured as an ejector (9) at the location of the oxygen-containing gas inlet (8), so that the gas delivered to the reactor will function to drive reactants and reaction products around the closed circuit. The invention also relates to a reactor for carrying out the inventive method.