A theoretical equation was developed to predict the enrichment produced by a single stage porous Vycor diffusion cell as a function of temperature. The separations of five binary gas mixtures were measured experimentally over a temperature range of 80 to 600°K. The agreement between theoretical predictions and experimental results was good over most of the temperature range. The largest deviations occurred when the operating temperature approached the critical temperatures of the gases. Mixtures of oxygen-carbon dioxide and helium-nitrogen were observed to become nonseparative at predicted temperatures. Overall, both separation and separative capacity were observed to increase with a decrease in temperature.