This study investigates autothermal reforming (ATR) of fuel cell-grade methanol as a method for producing hydrogen for transportation applications. From previous work in autothermal reformation, it is clear that while the steam-to-carbon ratio (S/C) may somewhat affect the efficiency of ATR, the oxygen-to-carbon ratio (O(2)/CH(3)OH) is a more significant parameter in ATR of higher hydrocarbons. According to past studies, the Optimum O(2)/CH(3)OH for ATR of methanol is equal to 0.23. However, this conclusion is based on models which utilize assumptions that are not necessarily accurate. This study presents experimental data that shows how ATR reactor efficiency varies with O(2)/CH(3)OH. Reactor efficiency data is compared to equilibrium model outputs in order to quantify the effect of O(2)/CH(3)OH as well as validate the equilibrium model. The results from this study serve as a baseline for future research of autothermal reforming of hydrocarbon fuels as a method for producing hydrogen in real applications. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.