Gas transport of carbon dioxide, oxygen, nitrogen and methane gases in a series of poly(phenylene thioether imide)s based on 2,2-bis(3,4-decarboxyphenyl) hexafluoropropane dianhydride and diamine-terminated oligo(phenylene thioether)s has been investigated. The effects of the oligo(phenylene thioether) length on the gas permeabilities and diffusivities were determined and correlated with chain packing of the polymers. The incorporation of a long oligo(phenylene thioether) segment in the polymer backbone decreases gas permeability and permselectivity simultaneously. The decreases in permeability coefficients can be related to decreases in both the diffusion coefficients and the solubility coefficients of all the gases. Finally, the physical and gas transport properties are simply compared between poly(phenylene thioether imide)s and poly(phenylene thioether).