The solubility and diffusion coefficients of pure carbon dioxide and its mixtures with methane, ethylene, and propylene in poly(4,4'-hexafluoroisopropylidene diphthalic anhydride-2,3,5,6-tetramethyl-1,4-phenylenediamine) (6FDA-TMPDA) membranes were determined with proton and C-l3 NMR spectroscopy and pulsed-field gradient NMR, respectively. In addition, the solubility and permeability of the pure gases in the polyimide membranes were also measured by sorption and permeation methods. The results showed that NMR measurements on pure gases are very reproducible and in relatively good agreement with those determined by the other methods. Furthermore, the NMR method allows the independent measurement of the solubility and diffusion coefficients for each component in mixtures of two or three gases and subsequently the gas permeability. The main conclusion of this work is that NMR spectroscopy is a suitable tool to determine all transport coefficients of multicomponent gas mixture in polymer membranes, provided that gas molecules contain NMR observable nuclei.