The transport behaviour of CO₂, N₂, and O₂ through polyetherurethane membranes were studied at different pressure and temperature. The permeability (P) and diffusion coefficient (D) obtained by time-lag method were increased with increasing pressure, temperature and molecular weight of diol, in the order CO₂>N₂>O₂. Jump lengths (λ) obtained from the activation energy of diffusion and the cohesive energy density of polyurethane were 50A°for PU-1 and 49A° for PU-2. The entropy of activation (ΔS^#) for diffusion was negative indicating that the dipolar interaction between Permeant and membrane was small, but the flexibility of soft segment in polyurethane was large.