The invention relates to a method for producing fuel from organic waste or biomass in a gasification process comprising the burning of organic waste or biomass and the recovery of the gasification residue. The method comprises at least the following steps: organic aqueous waste or biomass (M; M1) is fed in a combustion chamber (1); oxygen-bearing pressurized regeneration gas (G) is also fed in said combustion chamber (1); a continuous, pressurized combustion process is maintained in the combustion chamber, without adding an external oxygen source or heat in the process, so that the combustion of organic waste or biomass is carried out with the oxygen content of 0.1-1 of the stoichiometric oxygen content, as the oxygen maintaining the combustion and the overpressure and heat created in the combustion chamber (1) are completely derived from the pyrolysis of the regeneration gas and/or from the pyrolysis of the aqueous organic waste or biomass (M; M1) fed in the combustion chamber, and from the gasification reactions between the supplied material (M1) and the regeneration gas (G); ash (A) created in the continuous gasification process taking place in the combustion chamber (1) is removed and combustion gases obtained from the gasification process, together with solid particles contained in the combustion gases, are conducted to a separation process; in the separation process, the temperature of the combustion gas (S) is dropped below the flash point (Fp) of the compounds contained in the combustion gas and below the water condensation point, the condensation water (W) contained in the combustion gas (S) removed, the liquid fuel (M; M4) is recovered from the combustion gas (S) and the regeneration gas (G) contained in the combustion gas is completely or partly conducted back to the combustion chamber (1).