Composite carbon molecular sieve membranes (c-CMSM) were prepared in a single dipping-drying-carbonization step from phenolic resin solutions (12.5-15 wt.%) loaded with boehmite nanoparticles (0.5-1.2 wt.%). A carbon matrix with well-dispersed Al2O3 nanowires was formed from the decomposition of the resin and dehydroxylation of boehmite. The effect of the carbon/Al(2)O(3)ratio on the porous structure of the c-CMSM was accessed based on the pore size distribution and gas permeation toward N-2, O-2, CO2, He, H-2, C3H6 and C3H8. c-CMSM with higher carbon/Al2O3 ratios had a more open porous structure, exhibiting higher permeabilities and lower permselectivities. c-CMSM performance was above the upper bound curves for polymeric membranes for several gas pairs, particularly for C3H6/C3H8 (permeability toward C3H6 of 420 barrer and permselectivity of 18.1 for a c-CMSM with carbon/Al2O3 ratio of 4.4). Unsupported films were also prepared (carbon/Al(2)O(3)ratio 7.3) and crushed into small flakes. Equilibrium isotherms of H-2, N-2, O-2, CO2, C3H8 and C3H6 at 293 K were determined on these flakes to obtain the kinetic and adsorption selectivities toward gas pairs of interest; obtained adsorption and diffusion coefficients accurately predicted the permeabilities of all studied gases except CO2 (experimental and predicted permeabilities of 1148 and 154 barrer, respectively). (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.