In the present work, membranes from commercially available Pebax (R) 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 (H-2, N-2, CH4, CO2) and the obtained permeabilities were correlated with polymer properties and morphology of the membranes. The permeability Of CO2 in Pebax (R)/PEG membrane (50 wt.% of PEG) was increased two fold regarding to the pristine Pebax (R). Although CO2/N-2 and CO2/CH4 selectivity remained constant, an enhancement Of CO2/H-2 selectivity (similar to 11) 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. (c) 2007 Elsevier B.V. All rights reserved.