A process (10) for synthesising hydrocarbons includes feeding a gaseous feedstock (18) comprising hydrogen and carbon monoxide, into a first Fischer-Tropsch reaction stage (12) which is a three-phase low temperature catalytic Fischer-Tropsch reaction stage, and allowing the hydrogen and carbon monoxide partially to react catalytically in the first reaction stage (12) to form hydrocarbons. At least a portion of a tail gas (32) which includes unreacted hydrogen and carbon monoxide obtained from the first reaction stage, is fed into a second Fischer-Tropsch reaction stage (42) which is a two-phase high temperature catalytic Fischer-Tropsch reaction stage. The hydrogen and carbon monoxide are allowed at least partially to react catalytically in the second reaction stage (42) to form gaseous hydrocarbons.