The present study aims at understanding the effect of materials and operating conditions on the performance of in-house-prepared and vendor-supplied Nafion-based hydrogen-oxygen fuel cells. Eight different membrane electrode assemblies (MEAs) with different membrane thicknesses, two different equivalent weights for the membrane material, and made by three different MEA fabrication techniques, were investigated. The electrical performance and internal resistance of the cells were measured as a function of temperature and reactant pressures. The test results have been analyzed in terms of various polarization phenomena. The values for i(o,c) and alpha(c)n were generally in agreement with reports, but were found to have a range depending on the analysis conditions. While mass-transfer limitations were not observed in any of the cases, dry-out of the anode catalyst layer and "back-diffusion" were found to limit the maximum current densities, especially with the thicker membranes. The in-house-developed MEA fabrication process provides a lower internal resistance and higher performance during short-term testing when compared to the MEAs from the two industrial vendors studied. These results have led to the demonstration of a high-performance MEA for hydrogen-oxygen fuel cells based on Nafion 1035.