The gas permeability characteristics of poly(ethylene oxide-co-epichlorohydrin) films were determined by using the constant volume and pressure-increase method. Permeation measurements reveal that a wide range of gas transport properties can be obtained according to the ethylene oxide/epichlorhydrin ratio in the copolymer. The copolymers show very high permeability (up to 105 Barrer) and selectivity for carbon dioxide respect to nitrogen and methane (alphaCO(2)/N-2:63 and alphaCO(2)/CH4:17). The global mass transfer and selectivity seem to be controlled mainly by the carbon dioxide sorption mechanism and are directly related with the ethylene oxide content in the copolymers.