The fundamental gas transport properties of thin films of six high performance polymers were evaluated in the presence of silicon dioxide particles. The silica particles were brought in close contact with the polymer inside the 200 Angstrom. (DIA) pores of Anopore(TM) aluminum oxide membranes. This unique environment allows intimate contact between the polymer and the silica particles, The presence of silica improves the gas separation properties of the permselective layer, particularly for oxygen and nitrogen. The increase in O-2/N-2 selectivity for some membranes is accompanied by an increase in oxygen permeability. The oxygen/nitrogen separation properties of the polymers in the presence of silica falls above the so-called "upper limit of performance reported for polymeric materials. The observed significant increases in the glass transition temperature suggest restriction of chain segmental mobility possibly due to adsorption of polymer to silica surface, The increase in the activation energy of permeation points to increases in energetics of diffusion as the reason for the improved selective permeation, The observed behavior was not limited to oxygen and nitrogen as demonstrated by the results for other gas pairs tested.