An experimental work has been performed in order to study the pressure drop in air-forced open-cathode PEMFC architectures. Measurements have been obtained in an experimental setup specifically designed for the present research. Three different cathode configurations with aspects ratios (w(c)/h(c)) from 0.83 to 2.5, as well as different flow conditions have been studied, varying the Reynolds number from 45 to 4000. It has been verified that for the laminar region the pressure drop is proportional to the air velocity. For the present experiments, the boundary between the laminar and the transitional turbulent region has been established for a Reynolds number of 500. Two different equations have been obtained to estimate the friction factor, f, one for the laminar flow and the other for the transitional-turbulent region. Using these equations, an excellent agreement between measured and predicted friction factors has been achieved for the entire range of experimental conditions (Re, w(c), h(c)) tested in this research. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.