Previously, we reported on using room temperature ionic liquids (RTILs) in place of traditional solvents in liquid membranes and showed that stabilized RTIL-membranes outperformed standard polymers for the separations Of CO2/CH4 and CO2/N-2 (considering ideal gas permeabilities). Here, we report on mixed-gas permeances and selectivities for the gas pairs CO2/CH4 and CO2/N-2 using continuous flows of the mixed gases at various carbon dioxide concentrations (up to 2 bars Of CO2 partial pressure). Under mixed-gas test conditions, three of the tested membranes still operated with commercially attractive mixed-gas selectivity combined with CO2-permeability for CO2/CH4 separations. In addition, one of the tested membranes is, potentially, economically viable for CO2 capture from flue gas. We answer three objections to reduction-to-practice of RTIL-membranes for gas separations; namely, mixed-gas operations did not reduced the gas selectivities, membranes give advantageous performance even under dry gas feed conditions, and we achieved long-term stability in continuous operation, up to 106 days, without performance degradation. Furthermore, the RTIL-membranes operated under CO2-partial pressures of at least 207 kPa without decrease in separation ability. The RTIL-membranes tested include [emim][BF4], [emim][dca], [emim][CF3SO3], [emim][Tf2N], and [bmim][BETI]. (c) 2008 Elsevier B.V. All rights reserved.