Thermodynamic equilibrium of ethanol steam reforming has been studied by Gibbs free energy minimization method for hydrogen production in the ranges of water-to-ethanol ratio from 0 to 20, reaction temperature from 400 to 2000 K, pressure from 1 to 60 atm, argon-to-ethanol ratio from 0 to 100. The optimal conditions suitable for the use in molten carbonate fuel cell and solid oxide fuel cell were obtained as follows: 900-1200 K, water-to-ethanol ratio of 3:6, and 1 atm. Under the optimal conditions, complete conversion of ethanol, 60.52-83.58% yield of hydrogen and 32.82-79.60% yield of carbon monoxide could be obtained and no coke forms. Higher pressures have a negative effect, but inert gases have a positive effect, on the hydrogen yield. Coke tends to form at lower temperatures and lower water-to-ethanol ratios. Copyright (c) 2008 John Wiley & Sons, Ltd.