The Fraunhofer Institute for Solar Energy Systems (ISE) has developed, built, and operated an autothermal bio-ethanol reformer to generate hydrogen for fuel cell systems. The autothermal reformer has a high dynamics and electrical output of several hundred watts. The starting points for the design of the reactor were equilibrium simulations using CHEMCAD software. Significant process parameters considered included preheat temperature of the feed, steam/carbon (S/C) ratio, excess air coefficient, and reformer temperature. At about 700°C there was a high yield of hydrogen and CO. In a connected water gas shift reactor the CO was a reactant to produce hydrogen. The undesired formation of methane was negligible. The S/C carbon ratio was studied between 0.5:1 and 2.5:1. The data and simulations agreed well. Even at low S/C ratio of 0.5:1 the measured methane concentrations were < 0.3%. The CO concentration decreased with increasing S/C ratio and the hydrogen concentration increased. A high S/C ratio requires a higher energy input but eases the CO conversion by the shift reaction that for example is needed for PEM fuel cells. The process conditions can be adjusted to whatever fuel cell type is used.