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For the envisaged large number of commercial-scale carbon capture and storage (CCS) projects that are to be implemented in the near future, a number of issues still need to be resolved, the most prominent being the large capital and operational costs incurred for the CO₂ capture and compression process. An economic assessment of the capture and compression system based on optimal design data is important for CCS deployment. In this paper, the parametric process design approach is used to optimally design coal and natural gas monoethanolamine (MEA)-based post-combustion CO₂ absorption–desorption capture (PCC) and compression plants that can be integrated into large-scale 550 MW coal-fired and 555 MW natural gas combined cycle (NGCC) power plants, respectively, for capturing CO₂ from their flue gases. The study then comparatively assesses the energy performance and economic viabilities of both plants to ascertain their operational feasibilities and relative costs. The parametric processes are presented and discussed. The results indicate that, at 90% CO₂ capture efficiency, for the coal PCC plant, with 13.5 mol.% CO₂ in the inlet flue gas, at an optimum liquid/gas ratio of 2.87 kg/kg and CO₂ lean loading of 0.2082 mol CO₂/mol MEA, the CO₂ avoidance cost is about $72/tCO₂, and, for the NGCC PCC plant, with 4.04 mol.% CO₂ in the inlet flue gas, at an optimum liquid/gas ratio of 0.98 kg/kg and CO₂ lean loading of 0.2307 mol CO₂/mol MEA, the CO₂ avoidance cost is about $94/tCO₂.