An experimental and theoretical study has been used to investigate gas diffusion and solubility in PEBAX (R) 2533 block copolymer membrane. Molecular simulations using COMPASS force field have been successful in predicting the gas-transport properties of a PEBAX (R) 2533 block copolymer and of a pure PTMO homopolymer. Gusev-Suter transition state theory (TST) and Monte Carlo methods are used for simulating the transport of five permanent gases (He, H-2, N-2, O-2, CO2 and CH4). Theoretical and experimental data have been compared. (C) 2008 Elsevier B.V. All rights reserved.