AbstractIn the present work, membranes from commercially available Pebax® MH 1657 and its blends with low molecular weight poly(ethylene glycol) PEG were prepared by using a simple binary solvent (ethanol/water). Dense film membranes show excellent compatibility with PEG system up to 50 wt.% of content. Gas transport properties have been determined for four gases (H2, N2, CH4, CO2) and the obtained permeabilities were correlated with polymer properties and morphology of the membranes. The permeability of CO2 in Pebax®/PEG membrane (50 wt.% of PEG) was increased two fold regarding to the pristine Pebax®. Although CO2/N2 and CO2/CH4 selectivity remained constant, an enhancement of CO2/H2 selectivity (not, vert, similar11) was observed. These results were attributed to the presence of EO units which increases CO2 permeability, and to a probable increase of fractional free-volume. Furthermore, for free-volume discussion and permeability of gases, additive and Maxwell models were used.