Kinetic and mass transport parameters are determined for the oxygen reduction reaction at the interface between a 50 mu m radius platinum disk electrode and two solid polymer electrolyte membranes - Nafion(R) 117 (Du Pont) and a BAM(R) 407 membrane (Ballard Advanced Materials Corporation). These materials are investigated over a range of temperatures (303-343 K) and oxygen pressures (2-5 atm absolute), at 100% relative humidity, using a solid-state electrochemical cell. Slow-sweep voltammetry yields exchange current density data, while chronoamperometry allows determination of the diffusion coefficient and solubility, for the different conditions specified. This information is used to calculate activation energies for the oxygen reduction process and for diffusion of oxygen in the membranes, as well as the enthalpies of dissolution. Nafion(R) 117 and the BAM(R) 407 membrane have similar permeabilities (D(b)c(b) values), however, the diffusion coefficients and solubilities of oxygen are very different - being related to the water content of the respective material. Both membranes exhibit a Henry's Law dependence for the limiting current of the oxygen reduction reaction with increasing oxygen pressure.