A passive liquid feed direct methanol fuel cell (DMFC) with neither liquid pump nor a gas compressor was tested at different orientations. The experimental results showed that the vertical operation always yielded better performance than did the horizontal operation. It was further demonstrated that the improved performance in the vertical orientation was caused by the increased operating temperature as a result of a higher rate of methanol crossover, which resulted from the stronger natural convection in the vertical orientation. The constant current discharging tests showed that, although the vertical operation of the passive DMFC can yield better performance, the fuel utilization at this orientation is lower as a result of the increased rate of methanol crossover. It was also shown that the horizontal orientation with the anode facing upward rendered an effective removal of both CO2 bubbles on the anode and liquid water on the cathode and thereby a relative stable operation. Finally, it was revealed that the horizontal orientation with the anode facing downward exhibited rather unstable and short discharging duration because of the difficulties in removing CO2 bubbles from the anode and the liquid water from the cathode at this particular orientation. (c) 2005 Elsevier B.V. All rights reserved.