Abstract: The invention concerns a method and a plant for producing hydrocarbon based fuels from waste and biomass including wood and/or other cellulose containing biomass, where biomass and/or waste is gasified in anaerobic conditions, heating the formed syngas in for decomposition and subsequent condensation in anaerobic conditions, subjecting the heat treated biosyngas to cleaning measures for removing elements/compounds which are poisonous towards the catalysts of the Fischer-Tropsch synthesis, and passing the cleaned heat treated biosyngas through a Fischer-Tropsch synthesis for production of biofuels.