Magnesium oxide nanoparticles (3 nm) were dispersed in 1,2-polybutadiene via solution casting. Particles were observed to be dispersed into submicron aggregates using atomic force microscopy and transmission electron microscopy. The nanocomposite density was consistently lower than that anticipated on the basis of an additive model, suggesting the presence of voids in the nanocomposites. The incorporation of nanoparticles into 1,2-polybutadiene increased acid gas (i.e., CO2) and nonpolar gas (i.e., CH4, N-2) permeability with increasing particle loading. For instance, CO2 permeability increased from 52 barter in the unfilled polymer to 650 barrer in a nanocomposite containing 27 vol % (nominal) MgO, at 35 degrees C and a feed pressure of 12 atm. CO2/nonpolar gas selectivity decreased with increasing particle loading, while CH4/N-2 selectivity was not influenced by the particles. Gas solubility increased systematically with-increasing particle loading. In contrast, gas diffusion coefficients initially decreased with increasing particle loading and then increased with increasing loading at particle loadings greater than 10 vol % (nominal).