This paper describes the design, manufacturing, operation, and optimization of a mobile ethanol reformer fuel cell system for off-grid power production. The reformer system includes an autothermal reformer, high and low temperature shift reactors, a selective methanation reactor, and a tail gas combustor. A minimum amount of process controls and little internal heat integration kept system architecture simple. Process simulations provided optimal operating parameters, expected hydrogen yield, and system efficiency. The reformer temperature was selected to be 730 degrees C with minimal methane production and no soot formation in the reactor. The oxygen-to-steam ratio is determined by the temperature of feed streams, reforming temperature and heat losses. It was set to be in the order of 0.9. The steam-to-carbon ratio has no impact on carbon monoxide concentration (on a dry basis) in the reformer system product gas, i.e. at the outlet of the selective methanation reactor. Therefore, it was selected to be 2.5, sufficiently high to avoid soot formation in the reforming reactor and yet small enough to keep the size of the water evaporator in a sensible range. The reformer fuel cell system was operated in a lab environment and all reactors were thoroughly investigated. Main focus was to keep the carbon monoxide concentration at the outlet of the selective methanation reactor below 10 ppmv at all times. Furthermore, start-up and shut down procedures were optimized to minimize degradation of the catalysts. Finally, the complete reformer fuel cell system was operated to investigate its performance. System controls allowed fully automated operation of the integrated reformer fuel cell system. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.