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Studies of CO2 capture using membrane technology from coal-fired power-plant flue gas typically assume compression of the feed to achieve a driving force across the membrane. The high CO2 capture cost of these systems reflects the need to compress the low-pressure feed gas (1 bar) and the low CO2 purity of the product stream. This article investigates how costs for CO2 capture using membranes can be reduced by operating under vacuum conditions. The flue gas is pressurized to 1.5 bar, whereas the permeate stream is at 0.08 bar. Under these operating conditions, the capture cost is U.S. $54/tonne CO2 avoided compared to U.S. $82/ tonne CO2 avoided using, membrane processes with a pressurized feed. This is a reduction of 35%. The article also investigates the effect on the capture cost of improvements in CO2 permeability and selectivity. The results show that the capture cost can be reduced to less than U.S. $25/tonne CO2 avoided when the CO2 permeability is 300 barrer, CO2/N2 selectivity is 250, and the membrane cost is U.S. $10/m2.