The selectivity curves of gaseous binary mixtures of ethane + ethylene, methane + carbon dioxide at 303 K and 700 kPa and butane + 2 methylpropane at 318 K and 200 kPa are been determined on activated carbon and silica gel using an original apparatus. In this paper, a brief description of this apparatus is given. The difference in behavior of these two adsorbents is discussed.