NOVELTY - Synthesis of hydrocarbons involves reforming hydrocarbon feedstock containing inert gas, to generate synthesis gas containing inert gas/steam/hydrogen/carbon monoxide; cooling the synthesis gas to below the dew point to condense water and removing the water to give a de-watered synthesis gas; synthesizing hydrocarbons from the de-watered synthesis gas by the Fischer-Tropsch reaction, to give a tail gas; subjecting the mixture to water-gas shift reaction, thus forming shifted tail gas; subjecting the shifted tail gas stag of membrane separation; and using hydrogen-containing gas mixture.    USE - For synthesis of hydrocarbons (claimed), which is used as fuel.    ADVANTAGE - The process reduces the need for hydrogen to be supplied for hydrodesulfurization from separate hydrogen plant, and therefore reduces the size of the separate hydrogen plant. The recovery of hydrogen rich permeate stream allows more natural gas to be processed, with a higher production of Fischer Tropsch products for the same oxygen usage in the reforming section.    DETAILED DESCRIPTION - Synthesis of hydrocarbons involves reforming a hydrocarbon feedstock containing at least one inert gas in at least one reforming stage to generate a synthesis gas containing the inert gas, steam, hydrogen and carbon monoxide; cooling the synthesis gas to below the dew point to condense water and removing the water to give a de-watered synthesis gas; synthesizing hydrocarbons from the de-watered synthesis gas by the Fischer-Tropsch reaction and separating at least part of the synthesized hydrocarbons, to give a tail gas containing the inert gases, hydrogen, carbon monoxide and carbon dioxide; subjecting a mixture of at least part of the tail gas and steam to the water-gas shift reaction, thus forming a shifted tail gas having increased hydrogen and carbon dioxide contents; subjecting the shifted tail gas to at least one stag of membrane separation, thus generating an inert gas-containing gas mixture and at least one of hydrogen-containing gas mixture, a carbon dioxide-containing gas mixture and hydrocarbon-containing gas mixture; and using at least one of the hydrogen-containing gas mixture, the carbon dioxide-containing gas mixture and the hydrocarbon-containing gas mixture in a reformer feed stream.