An experimental study of the separation of m- and p-diethylbenzene (DEB) from a mixture containing the weight composition 66.7% m-DEB and 33.3% p-DEB on silicalite has been undertaken using high-pressure carbon dioxide and propane. The high-pressure gases functioned both as a carrier and a desorbent. The results show that the most appropriate operating combinations for obtaining 100% recovery of DEB isomer with a purity of over 99% and the smallest mean retention time for m-DEB was achieved by utilizing CO2 and propane at 34.0 atm, 363 K and 30 cm3/min, and at 6.8 atm, 443 K and 15 cm3/min, respectively. With these various combinations, the mean retention time of m-DEB was 149.7 min and 84.4 min using CO2 and propane, respectively. Accommodation to the operating temperature in the DEB production plant, and taking account of the compression costs and the operation time required, suggests the use of propane to achieve separation.