The effect of H2O vapor on the adsorption and desorption of CO2 and vice versa, both on a commercially viable solid amine sorbent (SAS), were studied using a thermogravimetric analyzer at constant temperature. The SAS was prepared by physically immobilizing PEI (Mn 423) in a porous silica (CARiACT G10). Studies were carried out at two concentrations of CO2 (2 vol % in N-2 and 100 vol %), one concentration of H2O vapor (2 vol %), and four temperatures (40, 60, 80, and 100 degrees C). The results revealed three separate and identifiable mechanisms or processes taking place on the SAS, i.e., the individual adsorption of CO2 or H2O and the coadsorption of H2O and CO2. The individual adsorption of either CO2 or H2O was noncompetitive or completely independent of each other thermodynamically for both concentrations of CO2 and all four temperatures. In addition, the individual adsorption of CO2 was fully reversible, while the individual adsorption of H2O was only partially reversible. The coadsorption of CO2 and H2O was exothermic, with either irreversible or very slow desorption kinetics. Coadsorption was observed appreciably only at 60 and 40 degrees C at both CO2 concentrations and only very slightly at 80 degrees C and 2 vol % CO2. It was not observed at 100 degrees C at either CO2 concentration or at 80 degrees C at 100 vol % CO2. The influence of CO2 or H2O on the kinetics of any of these processes was revealed only at the two lower temperatures, with H2O having a positive influence on the desorption kinetics of CO2 at 40 degrees C and with CO2, if adsorbed previously, having a negative influence on the adsorption kinetics of both H2O and the coadsorption of both CO2 and H2O at both 60 and 40 degrees C. When these effects existed, they were not that significant, at least not at 2 vol % H2O vapor. Overall, these results thus indicated that the effect of H2O vapor in the feed of a CO2 stream does not have to be accounted for mechanistically when modeling a cycle adsorption process based on this commercially viable SAS.