In this work we investigate the performance of high flux chemical vapour deposition (CVD) silica membranes for the separation of gas mixtures containing H-2 and CO2 at various temperatures. The membranes were prepared by a counter diffusion CVD method where tetraethyl orthosilicate (TEOS) and (O-2 were used as reactants. Single gas permeation resulted in activated transport for the smaller kinetic diameter gases (H-2 and He) whilst the larger kinetic diameter gases (CO2 and N-2) showed negative activation energy. The single gas permeation of H-2 increased from 5.1 x 10(-7) to 7.0 x 10(-7) Mol m(-2) s(-1) Pa-1 in the temperature range 100-400 degrees C. and H-2/CO2 and H-2/N-2 selectivities reached 36 and 57 at 400 degrees C, respectively. The H-2 purity in the permeate stream also increased with temperature for H-2:CO2 binary gas mixture, thus being beneficial for H-2 diffusion. H-2 competitively permeated through the membrane at a several range of gas mixtures. and a saturation level was achieved at H-2:CO2 60:40 feed concentration, where the diffusion of CO2 molecules became negligible delivering similar to 99% H-2 purity in the permeate stream. These results substantiate that the counter diffusion CVD method produced thin silica film membranes with a very precise pore size control, in particular suggesting a narrow pore distribution with average pore radius of about 3.1 angstrom. (C) 2008 Elsevier B.V. All rights reserved.