Thermodynamic equilibrium of ethanol steam reforming is studied using the Gibbs free energy minimization method. The reaction paths of ethanol steam reforming are simulated using Chem-CAD software. Appropriate optimization of reactants ratio and reaction conditions is performed, to achieve the composition of ethanol steam reforming products, which will be favorable as an internal combustion engine (ICE) fuel. The effects of process variables, such as temperature and water : ethanol molar ratio are discussed. Numerical investigations are conducted to analyze energy performance of steam reforming of ethanol for ICE. Realization of ethanol steam reforming at high temperature leads to an increase in efficiency of the process. The optimal conditions are obtained as follows: 1100 K, water : ethanol molar ratio of 1.2. Copyright © 2011 John Wiley & Sons, Ltd.