Natural gas steam reforming process comprised in a small scale H-2-fueling station for on-site hydrogen production was simulated and analyzed. The effects of process variables on the process efficiency of hydrogen production were investigated, and their optimum set point values were suggested to minimize the sizes of the process sub-units and to secure a stable operability of the reforming process. Steam to carbon (S/C) ratio of the reforming reactants was found to be a crucial parameter mostly governing both the hydrogen production efficiency and the stable operability of the process. In this study, a process run was assumed stable if feed water (WR) as a reforming reactant could have been completely evaporated into dry steam through a heat recovery steam generator (HRSG). The optimum S/C ratio was 3.0 where the process efficiency of hydrogen production was maximized and the stable operability of the process was secured. The optimum feed rates of natural gas (NCR) and WR as reforming reactants and of natural gas (NGB) as a burner fuel were also determined for a target rate of hydrogen production, 27 Nm(3)/h. Set point temperatures of the combustion flue gas (CFG) and the reformed gas (RFG) from the reformer had no effects on the hydrogen production efficiency, however, they were important parameters affecting the stable operability of the process. The effect of the set point temperatures of the RFG from cooler and the CFG from HRSG on the hydrogen production efficiency was not much significant as compared to the SIC ratio, but needed to be adjusted because of their considerable effects on the stable operability of the process and the required heat transfer areas in cooler and HRSG. (C) 2011 Elsevier Ltd. All rights reserved.