Silica-impregnated, brominated PPO [poly(phenylene oxide)] (BPPO) membranes exhibit enhanced CO2 permeability relative to pure BPPO membranes due to higher gas solubility and especially higher gas diffusivity. Among the three silica sizes (2, 10, and 30 nm) characterized in this work, the 10 nm silica is found to result in the highest gas permeability, about 5 times higher than that of the pure BPPO membranes. These permeability enhancements do not cause an appreciable loss of selectivity, which remains essentially unchanged, for example, about 21 for the CO2/N-2 separation and about 15 for the CO2/CH4 separation. The permeability increases with increasing silica content, which, however, cannot exceed about 0.35 silica/BPPO weight ratio due to a substantial increase in brittleness.