A generation 0 poly(amidoamine) (PAMAM), dendrimer in the immobilized liquid membrane (ILM) configuration was studied using flat films and hollow fibers for CO2-N-2 separation. This dendrimer as a pure liquid functions as a CO2-selective molecular gate with highly humidified feed gas (Kovvali et al. J, Aml Chem. Sec. 2000, 122, 7594). The present work broadens:the range of relative humidity of the feed gas stream (RHf) by adding a small amount of glycerol to the pure dendrimer liquid. A 75% dendrimer-25% glycerol ILM was found to increase-the operating range of RHf substantially while maintaining the CO2 permeance and the selectivity (alpha (CO2/N2)) close to the levels observed with a pure dendrimer ILM. The performances of pure and 75% dendrimer ILMs were found to be superior or comparable to the highest reported alpha (CO2/N2); This behavior is explained in ter;lis of the charged environment in the dendrimer liquid membrane under humidified feed conditions and facilitated transport Of CO2.