A fractional experimental design, at two levels and four factors, has been carried out in order to improve the power output of a commercial stack protonic exchange membrane (PEM) fuel cell with seven graphite plates at about atmospheric hydrogen pressure. The factors considered were both hydrogen and oxygen pressures and flow rates. An orthogonal and fractional matrix array was used in order to reduce time execution with eight experiments instead of the full factorial design of 16 experiments. The experiments showed that not all the conditions have stable power output with the considered hydrogen pressure, but that it is possible to stabilize it especially with high oxygen flow rates. A comparison has been carried out between this commercial fuel cell and PEM fuel cell device manufactured in Mexico by Monterrey Technology Institute and Advanced Studies, Mexico City Campus (ITESM CCM). (C) 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.