Gas permeabilities and permselectivities for He, H-2, CO2, Ar, O2, N2 and CH4 are reported for two series of segmented 6F polyimides containing oligo (phenylene thioether) and oligo (phenylene sulfone) segments. In both polyimide series, glass transition temperatures and ps permeabilities decreased with increasing segment length, while pure gas permselectivities were not affected. In comparison to the 6F poly(arylene thioether imide)s, the corresponding 6F poly (arylene sulfone imide) s, prepared by oxidation of the poly (thioether imide) s, exhibited higher flux combined with higher permselectivities. In the case Of CO2 permeation, this behavior could be attributed to higher CO2 solubilities of polyimides containing the sulfone moieties.