<p>Method of producing a hydrocarbon composition. The method comprises providing a biomass raw-material; gasifying the raw-material in the presence of oxygen to produce a gas containing carbon monoxide, carbon dioxide, hydrogen and hydrocarbons possibly together with inert components; separately increasing the hydrogen-to-carbon monoxide ratio of the gas to a value of about 2; feeding the gas to a Fischer-Tropsch reactor; converting in the Fischer-Tropsch reactor at least a significant part of the carbon monoxide and hydrogen contained in the gas into a hydrocarbon composition containing C4-C90 hydrocarbons; and recovering the hydrocarbon composition. According to the invention, fresh external hydrogen is introduced into the gas before feeding into the Fischer-Tropsch reactor. By using external hydrogen feed, the capacity of a biomass gasification process can be increased and the need for a conventional Water Gas Shift for producing hydrogen from carbon monoxide and steam can be eliminated.</p>
