A method is described for conversion of natural gas or other fossil fuels to higher hydrocarbons, comprising the following steps: a) reaction of natural gas with steam and oxygenic gas in at least one reforming zone in order to produce a synthesis gas consisting primarily of hydrogen and CO, in addition to some carbon dioxide; b) passing said synthesis gas to a Fisher-Tropsch reactor in order to produce a crude synthesis stream consisting of lower hydrocarbons, water and non-converted synthesis gas; c) separation of said crude synthesis stream in a recovery zone, into a crude product stream mainly containing heavier hydrocarbons, a water stream and a tail gas stream mainly containing the remaining constituents; which is charaterized in that the method also comprises the following steps; d) stream reformation of at least part of the tail gas in a separate steam reformer; e) introduction of the reformed tail gas into the gas stream before this is led into the Fischer-Tropsch reactor.