CO2 fugacity difference is the driving force for CO2-selective membranes used in post-combustion capture. The ambient pressure of the flue gas makes it very difficult to use only a single membrane stage to achieve the CO2 purity required by pipeline transport and storage, e.g., 95?mol.-%. On the basis of a general multi-stage membrane concept, an energy-efficient membrane cascade is developed. The correlation of energy consumption and membrane area of a cascaded membrane process is investigated, considering 50?%, 70?%, and 90?% degree of CO2 separation. In addition to an idealized flue gas consisting of N2 and CO2 only, also a quasi-real flue gas is studied. Pressure loss in membrane modules and their influence on process energy consumption are discussed.