The cost-effectiveness of carbon sequestration alternatives has often been discussed in the economics literature on sequestration. Average or marginal costs and annual carbon supply curves are often used as measures of cost-effectiveness. Sequestration is inherently a temporal process and how time is accounted for in the various measures of cost-effectiveness is critical for appropriate cross-study comparisons. I examine three factors that affect the magnitude of measured cost-effectiveness: the study period, the sequestration path, and the discount rate if discounting is used. The extent to which these factors affect the consistency of cross-study comparisons is empirically illustrated.