NOVELTY - Performing Fischer-Tropsch synthesis on a feed gas comprising carbon monoxide and hydrogen, uses compact catalytic reactor modules (12a, 12b) and is performed in at least two successive stages.    USE - The invention is used for performing Fischer-Tropsch synthesis on a feed gas comprising carbon monoxide and hydrogen.    ADVANTAGE - The invention enables the method to be varied to match variations in the supply of natural gas over time, without disturbing the operating conditions within the Fischer-Tropsch modules.    DETAILED DESCRIPTION - Performing Fischer-Tropsch synthesis on a feed gas comprising carbon monoxide and hydrogen to generate a hydrocarbon product uses compact catalytic reactor modules each defining flow channels for the Fischer-Tropsch synthesis in which are gas-permeable catalyst structures, and adjacent flow channels for a heat transfer medium, where the Fischer-Tropsch synthesis is performed in at least two successive stages, and there are the same number of reactor modules for each of the successive stages, all the reactor modules providing identical flow channels, in the first stage the gas flow velocity being sufficiently high and the temperature sufficiently low that not greater than 75% of the carbon monoxide undergoes conversion, the gases being cooled between successive stages to condense water vapor and some of the hydrocarbon product, and then being subjected to the second stage.    An INDEPENDENT CLAIM is also included for a plant (10) for performing Fischer-Tropsch synthesis on a feed gas comprising carbon monoxide and hydrogen, comprising compact catalytic reactor modules each defining flow channels for the Fischer-Tropsch synthesis in which are gas permeable catalyst structures, and adjacent flow channels for a heat transfer medium, the reactor modules being arranged such that the Fischer-Tropsch synthesis occurs in at least two successive stages with the same number of reactor modules for each of the successive stages, all the reactor modules providing identical flow channels, the plant incorporating a cooling mechanism to cool the reactant gases between successive stages so as to condense water vapor and some of the hydrocarbon product.    DESCRIPTION OF DRAWING(S) - The figure shows a flow diagram of the plant for performing The Fischer-Tropsch synthesis.    Plant (10)    Compressor (11)    Reactor modules (12a, 12b)    Heat exchanger (15)