Carbon molecular sieve membranes (CMSM) from Carbon Membranes Ltd. (Israel) were characterized. These membranes possess a very narrow pore system, in the range of 0.3-0.5 nm, and a sharp pore size distribution, allowing for high selectivities and permeabilities in gas separations. Penetrants O-2, N-2, CO2, SF6, Xe and He were used in monocomponent adsorption, permeability and uptake experiments for obtaining adsorption and diffusion data, leading to new insights on the internal pore structure of CMSM. A number of complementary morphological characterizations were also performed. The permeability and adsorption data were obtained over a temperature range from 273 to 323 K and over a pressure up to 5 bar. A relation between the adsorption and permeability data was used, allowing for the estimation of the diffusivity coefficients, which were further compared with those directly obtained from the uptake experiments. Permeation and uptake experiments showed a similar strong dependence of CO2 diffusivity on concentration. (C) 2004 Elsevier B.V. All rights reserved.