Two simple and inexpensive volumetric adsorption/desorption methods have been developed for the collection of adsorption isotherm data for weakly adsorbed gases at moderate pressures. Adsorption of O2 and N2 on AlPO(4)-5 and SAPO-5 at 309 and 329 K and 500-3000 kPa has been studied using the two methods. Sips’ equation was found to give a good fit for the adsorption isotherm data for O2 and N2 on both adsorbents. The comparison of the relative adsorption of O2 and N2 on the two adsorbents indicates that AlPO4-5 is a better choice for its use in the O2/N2 separation from air.