The paper gives EPA's conclusions from analyses which led to the decision to propose percent reduction Federal new source performance standards (NSPS) to control air emissions of sulfur dioxide (SO2) from new industrial boilers. It summarizes the NSPS, proposed by EPA on June 19, 1986. The NSPS would require boiler owners to reduce SO2 emissions by 90% and meet an emission limit of 1.2 lb/million Btu of heat input for coal-fired boilers, and 0.8 lb/million Btu for oil-fired boilers. In developing the NSPS, several regulatory options were considered, from standards that could be met by firing low sulfur fuels to those that would require flue gas treatment. The environmental, economic, and cost impacts of each option were analyzed. National impacts were estimated by a computer model that projects the population of new boilers over the 5-years following the proposal, predicts the compliance strategy that will be used to comply with the particular option (always assuming that the lowest cost compliance method will be selected), and estimates the resulting emission reductions and costs. Impacts on specific industries and on model boilers were also analyzed.