In this work we describe the preparation of hybrid organic-inorganic films using the sol-gel process. Poly(ethylene oxide-b-amide-6), PEBAX, was used as an organic matrix. Silicon oxide or titanium oxide were prepared by hydrolysis and polycondensation of tetraethoxysilane, TEOS, or titanium tetraisopropoxide, TiOP, respectively. Hybrid films were characterized by electron microscopy, stress-strain tests and their gas permeability and selectivity properties were evaluated. Small angle X-ray scattering was used to investigate structural heterogeneity caused by the presence of SiO2 or TiO2 particles in the organic matrix. For films containing silicon oxide as an inorganic filler, gas permeability decreased as a function of the inorganic component content. When titanium oxide was used as a filler, gas permeability was considerably lower than that measured for films containing silicon oxide (80/20 PEBAX/inorganic precursor compositions). In these cases, the morphologies were very similar, but films containing titanium oxide were much more rigid. For CO2/N-2 and CO2/H-2 separation factors up to 52.9 and 7.1, respectively, were obtained for 80/20 PEBAX/TiOP films. For higher titanium oxide contents, gas permeability increased. In these cases, a TiO2 agglomeration was observed and the barrier performance decreased. Permeability and selectivity properties are discussed as a function of morphological and mechanical properties of these films. (C) 2000 Elsevier Science Ltd. All rights reserved.