Molecular simulation is used as a tool to improve understanding of CO2 adsorption in nitrogen-functionalized carbon sorbents in the presence of water vapor, which is crucial to the advancement of adsorption approaches to CO2 separation from exhaust streams of coal- and natural gas-fired power plants. Molecular simulations were carried out for binary mixtures of CO2 and H2O over four N-functionalized surfaces and three variations of the quaternary group with increasing wt % N. The quaternary group was found to be most stable with a 13% loss in CO2 capacity observed, followed by the pyrrolic and pyridonic groups, which lost 25 and 28% CO2 loading capacity, respectively. The oxidized pyridinic group demonstrated a dramatic loss in capacity, i.e., 58% when compared to ideal loading. The quaternary group was the only functionality to display loading in excess of 2.0 mmol CO2 g(-1) sorbent under ambient temperature and 1% humidity (2.40 mmol CO2 g(-1) sorbent). Further, the two functional groups without oxygen were shown to be more resistant to competitive H2O adsorption at low humidity. In general, increasing nitrogen content appears to buffer the CO2 capacity loss under low humidity, yet such systems appear to be incompatible with CO2 separation at ambient temperature and 10% humidity. Further, the results of this work suggest that materials modified with pyrrolic and pyridonic groups and pore size weighted in the supermicroporous region are most resistant to compromised CO2 loading under 10% humidity.