The separation of the mixtures of hydrocarbon vapors from nitrogen was studied by using an asymmetric aromatic poly(ether imide) membrane prepared by the phase inversion technique. The effect of the presence of water in the feed stream on the separation of hydrocarbon vapors from nitrogen and on the separation of gasoline vapor from nitrogen was also investigated. It was found that the asymmetric membrane is effective for the separation of hydrocarbon vapors from nitrogen without silicone rubber coating. It was also found that the permeability of water is far greater than those of hydrocarbon vapors.