We report here the results of our recent studies describing the preparation of carbon molecular sieve membranes, their separation and transport characteristics with gas mixtures, and their molecular simulation. Poly(furfuryl alcohol) (PFFA) was used as the polymeric precursor for the preparation of the carbon films. The membranes were tested using single gases H-2, CO2 CO,CH4, and Ar, as well as binary mixtures of CO2/CH4 and a four-gas mixture consisting of CO2/CO/H-2/CH4. Separation factors for CO2/CH4 in the range of 34-37 were obtained for the binary and, the;four-gas mixtures. The membrane permeance decreased slowly during continuous testing with the four-gas mixture. This decline in performance was found, however, to be reversible. The initial membrane permeance was recovered by heating the membrane in an inert atmosphere of Ar. Modeling of the membrane＇s transport characteristics was carried out using a nonequilibrium molecular dynamics simulation. The modeling results agree qualitatively with the experimental data.