Kinetic and mass transport properties were investigated for the oxygen reduction reaction in Nafion 117 and a sulfonated poly (arylene ether sulfone) membrane (SPES-40, 40% sulfonated groups/repeat unit) under 1 atm oxygen pressure, 100% relative humidity in a temperature range of 303-343 K using a solid-state electrochemical cell. Kinetic parameters were obtained using slow-sweep voltammetry while mass transport parameters, the diffusion coefficient (D) and solubility (C), were obtained using chronoamperometry at a Pt (microelectrode)/proton exchange membrane (PEM) interface. Oxygen reduction kinetics was found to be similar for both Nafion(R) 117 and SPES-40 membrane at the Pt microelectrode interface. The temperature dependence of O-2 permeation parameters showed same trends for both the membranes studied, there was an increase in D and a concomitant decrease in C. Despite lower equivalent weight and hence higher water content SPES-40 exhibited relatively close values of D with Nafion(R) 117. The results are discussed in the context of their different microstructures. Values of C showed a closer relationship to water. content and the percent volume of aqueous phase in the respective membranes. The values of overall oxygen permeability were significantly higher in Nafion(R) 117, with a higher positive slope in its variation with temperature. (C) 2003 Elsevier Science Ltd. All rights reserved.