Three-dimensional models of a plate methanol steam micro-reformer and a methanol catalytic combustor with parallel flow fields and serpentine flow fields have been established. The effects of the flow field design and the fuel flow rate on the methanol conversion and transport phenomena in the micro-reformer were investigated. The results revealed that the methanol conversion of the micro-reformer with the serpentine flow field and the combustor with the serpentine flow field has been optimized as a result of improved thermal management in the micro-reformer with combustor. With a change in flow field design from the micro-reformer and the combustor with parallel flow fields to the micro-reformer and combustor with the serpentine flow fields a wall temperature increase from 225 degrees C to 237 degrees C was observed. The methanol conversion of the micro-reformer with the serpentine flow field and the combustor with the serpentine flow field could be improved by 23% relative to the employment of a parallel flow field. A numerical model provided an efficient way to characterize the transport phenomena within the micro-reformer and combustor; the results will benefit the future design of plate methanol steam micro-reformers with combustors. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.