Novel nanocomposite membranes containing single walled carbon nanotubes inside a polysulfone matrix have been prepared and characterized. The carbon nanotubes were functionalized with long chain alkyl amines to facilitate dispersion in the polymer. Both permeabilities and diffusivities of the membranes increased with increasing weight fraction of carbon nanotubes at 4 atm. Experimental sorption isotherms of H-2, O-2,O- CH4 and CO2 were consistent with isotherms predicted by atomistic simulations. Comparison of CO2 adsorption of closed and open nanotubes with simulations of closed and partially open carbon nanotube bundles suggests that HiPco nanotubes are approximately 47% open. (C) 2007 Elsevier B.V. All rights reserved.