Further insight into the impact of air and humidity exposure on carbon molecular sieve membranes (CMSM) is provided. A CMSM was exposed to water vapor and to different dry environments (air, oxygen, nitrogen, propylene, etc.) for several months and the performance stability with time was analyzed periodically. In an effort to better understand the effect of oxygen on the fresh CMSM, regeneration at high temperature, used to remove some oxygen surface groups, was conducted I year after fabrication. The impact of oxygen removal from the surface on adsorption equilibrium, kinetic transport and pore structure is considered. Membrane aging as a result of oxygen adsorption was investigated on the heat-treated sample. This is the first time that oxygen chemisorption uptake rates have been measured on CMSM. Passivation methods and regeneration procedures on CMSM are also discussed. (C) 2007 Elsevier B.V. All rights reserved.