The transport parameters (permeability coefficients, separation factors) were determined for the separation of mixtures of n-butane and methane. The content of butane in the feed was in the range 3.7-7.9% and simulated the composition of associated petroleum gas. The experiments were carried out at room temperature and feed pressure of 2-6 atm. Novel membrane materials - poly(trimethylsilylnorbornene) and poly(bis-(trimethylsilyl)tricyclononene) - were studied in the form of dense films. Both polymers reveal a distinct solubility controlled permeation: the permeate streams were strongly enriched (up to 58%) with the heavier component (C(4)H(10)), the permeability of methane was reduced by a factor 3-4 as compared to the permeability of pure methane, and high permeability of butane was observed. Novel Si-containing poly(cycloolefins) as membrane materials were compared with high permeability polyacetylenes. (C) 2011 Elsevier B.V. All rights reserved.