Different syngas configurations in a gas-to-liquid plant are studied including autothermal reformer (ATR), combined reformer, and series arrangement of gas-heated reformer and ATR. The Fischer-Tropsch (FT) reactor is based on a cobalt catalyst and the degrees of freedom are steam-to-carbon ratio, purge ratio of light ends, amount of tail gas recycled to synthesis gas (syngas) and FT synthesis units, and reactor volume. The production rate of liquid hydrocarbons is maximized for each syngas configuration. Installing a steam methane reformer in front of an ATR will reduce the total oxygen consumption per barrel of product by 40 % compared to the process with only an ATR. The production rate of liquid hydrocarbons is increased by 25.3 % since the flow rate of the purge stream for the ATR is the highest one compared to other configurations and contains mainly CO2.