Studies of CO2 capture and storage (CCS) from coal-fired power plants typically assume a capture efficiency near 90%, although the basis for a particular choice usually is not discussed. Nor do studies systematically explore a range of CO2 capture efficiencies to identify the most cost-effective levels of CO, control and the key factors that affect such levels. An exploration of these issues is the focus of this paper. As part of the United States Department of Energy's Carbon Sequestration Program, we have developed an integrated modeling framework (called IECM-cs) to evaluate the performance and cost of alternative CCS technologies and power systems in the context of plant-level multipollutant control requirements. This paper uses IECM-cs to identify the most cost-effective level of CO, control using currently available amine-based CO2 capture technology for PC plants. Two general cases are of interest. First, we examine the effects of systematically increasing the CO2 capture efficiency of an amine-based system for PC applications over a broad range. We report two measures of cost: (i) capital cost and (ii) cost-effectiveness (cost per tonne of CO2 avoided) relative to similar plants without CCS. Second, we examine the cost-effectiveness of plant designs that partially bypass the amine capture unit so as to achieve low to moderate reductions of CO2, but at lower overall cost. Results from these cases are compared to the conventional case of a capture unit treating the entire flue gas stream. In each case, we identify the most cost-effective strategies and the key factors that affect those results.