Interest in the gas-to-liquid process (GTL) using Fischer-Tropsch reactors (F-T) has increased in recent years because of its potential to replace ordinary petroleum with sulfur-free fuels. However, the efficiency of the process is still low compared with current routes; a large amount of the initial exergy of the gas is used to convert it into liquid fuel. In the present study, we analyze the overall thermodynamic efficiency of a GTL process and point out the main sources of entropy production. Next, we use exergy analysis to establish the impact of catalyst selectivity and of thermal losses on the process efficiency. In particular, we report the effect of selectivity losses in the F-T reactor and reformer, and the impact of high-temperature heat integration across the reforming unit.