This paper discusses the effect of penetrant-induced conditioning on the gas transport properties of four fluorine-containing polyimide isomers. The effects of substitution of bulky groups within the dianhydride residue of the polyimide and isomerism of the diamine residue on the penetrant induced hysteresis of COd(2) permeability were investigated. The COz permeability in the polyimide films that had been conditioned with carbon dioxide at 60 atm are compared to those in the untreated films. Exposure of the polyimides to CO2 at 60 atm resulted in 4.5- to 10-foLd increases in the permeability of COz relative to unconditioned films. The permeability enhancement was a result of increases in both the solubility and diffusivity following conditioning. There was also a surprising maximum in the permeability at intermediate pressures in conditioned samples of two of the polyimides. The permeability of CO2 in the conditioned polymers initially increased with decreasing pressure, exhibited a maximum value at approximately 30 atm, and decreased in permeability at low pressures.