Mass transport properties were investigated by means of the chronoamperometry method for a series of sulfonated poly(arylene ether sulfone) (SPES) membranes and sulfonated polysulfide sulfone (SPSS) polymers of various ion exchange capacities (IEC) at a Pt (microelectrode)/proton exchange membrane (PEM) interface. The temperature and pressure dependence of oxygen transport parameters show similar trends for the SPES 30-60 (IEC = 1.2-2.2 meq g(-1)) and SPSS 20-50 (IEC = 0.7- 1.8 meq g(-1)) membranes. The diffusion coefficient was found to increase with the IEC while solubility decreases. The results are discussed in the context of water/polymer interactions and morphology-facilitated mass transport characteristics. © 2005 The Electrochemical Society. [DOI: 10.1149/1.1896529] All rights reserved.