The effect of small amounts of water, in regard to inhibiting the adsorption of carbon dioxide (CO2), on several different cationic forms of zeolite X has been investigated using the zero length column (ZLC) technique, coupled with temperature-programmed desorption (TPD) measurements. This is shown to be a very effective way to study the effect of a strongly adsorbed species (water) on the adsorption of a less-strongly adsorbed species (CO2 or propane (C3H8)). It was observed that, for all systems studied, the Henry constant declines exponentially with the loading of water. As expected, this effect is stronger for CO2 than for C3H8.