Variations in the cost of flue gas desulfurization systems were analyzed by examining (1) the factors affecting cost estimates, (2) actual costs, and (3) competitive bids. The principal factors affecting cost estimates are the date of the estimate, plant size and sulfur content of the fuel, degree of sulfur removal, operating variables, project scope, sludge disposal, by-products, retrofit problems, and business level. Analysis of actual costs for eight new lime/limestone systems produced a correlation of cost (1980 $/kW) as a function of capacity (MW). No correlation was found for retrofitted units nor was there any significant difference in investment requirements between lime versus limestone systems. Information on competitive bids was very limited but seemed to indicate that alternative specifications do not result in large price variations.