A simulation study on gas-to-liquid (natural gas to Fischer-Tropsch synthetic fuel) process was carried out in order to find optimum reaction conditions for maximum production of synthetic fuel. Optimum operating condition for GTL (gas-to-liquid) process was determined by changing reaction variable such as temperature. During the simulation, overall synthetic process was assumed to proceed under steady-state conditions. It was also assumed that physical properties of reaction medium were governed by RKS (Redlich-Kwong-Soave) equation. ATR (auto-thermal reforming) in synthesis gas production unit and slurry phase reaction over Co-based catalyst in FTS (Fischer-Tropsch synthesis) unit were considered as reaction models for GTL process. The effect of reaction temperature on CO conversion and C-5-C-20 hydrocarbon yield in FTS unit was mainly examined. Simulation and experimental results showed that optimum reaction temperature in FTS unit was 255 degrees C. Simulation results were also compared to experimental results to confirm the reliability of simulation model. Simulation results were reasonably well matched with experimental results. (C) 2009 Elsevier B. V. All rights reserved.