A micro-scale power supply is being developed to provide an alternative to current secondary batteries for use in microelectronics devices, such as microsensors. The work discussed in this paper expands on this earlier reported sub-watt power generation system. Two designs were evaluated: a processor optimized to improve the thermal efficiency of the methanol reforming reactor from 9 to above 20%, and a system tailored to decrease the carbon monoxide levels to below 500 ppm, preferably lower than 100 ppm. Each design was operated over a range of feed flow rates. Thermal efficiencies up to 33% were demonstrated with the optimized processor, likely as a result of the low operating temperature, high methanol concentration (similar to60 wt.%) in the feed, and the high hydrogen production. Up to 3.55 sccm hydrogen was produced with relatively low carbon monoxide. In the second design, significant decreases in carbon monoxide, in some cases below 100 ppm, were achieved while maintaining reasonable thermal efficiencies of up to 19%. (C) 2004 Elsevier B.V. All rights reserved.