gas transport coefficients for oxygen, carbon dioxide and nitrogen were determined. Sorption experiments of carbon dioxide were also performed in tricresylphosphate and in neat 6FDA-TMPD polyimide membrane. Additionally, the solubility and diffusion coefficients of [C-13]O-2 in the same materials were determined with C-13 pulsed field gradient NMR measurements. The analysis of the gas transport coefficients of the membranes as a function of the content in tricresylphosphate dearly showed an important decrease in solubility and permeability but with little influence on the permselectivity.Membranes were prepared with two polyimides (Matrimid and 6FDA-TMPD) having a content of tricresylphosphate ranging from 0 to 33% (w/w). The specific volumes of these membranes were used to determine the partial specific volume of tricresylphosphate in the membranes, the hypothetical specific volumes of the pure polyimides in the liquid state and the fraction of nonequilibrium excess free volume in the glassy state. Permeation measurements were carried out and the