The paper gives results of a study to improve engineering applying cost estimates currently being used to evaluate the economic effects of applying SO2 and NOx controls at 200 large SO2 emitting coal-fired utility plants in the U.S. To accomplish the objective, procedures were developed and used that account for site-specific retrofit factors. The site-specific information was obtained from aerial photographs, generally available data bases, and inputs from utility companies. Cost results are presented for the following control technologies: lime/limestone flue gas desulfurization, lime spray drying, coal switching, furnace and duct sorbent injection, low NOx injection or natural gas reburn, and selective catalytic reduction. Although the cost estimates provide useful site-specific cost information on retrofitting acid gas controls, the costs are estimated for a specific time period and do not reflect future changes in boiler and coal characteristics (e.g., capacity factors and fuel prices) or significant changes in control technology cost and performance.