In those regions of the U.S. where ambient air quality levels are in attainment of the National Ambient Air Quality Standards, operators of major new stationary sources of air pollution, or existing sources which undergo major modifications to their operations, are required by the Clean Air Act to obtain a PSD permit prior to beginning construction. Recently, there has been a lot of regulatory activity in some parts of the U.S. directed at industries that failed to file for such permits in the past, regardless of the reasons for their omission. Some industries are finding it necessary to review all of their projects over the past 25 years to ensure that there are no outstanding issues related to PSD permits. To obtain a PSD permit it is required to conduct an analysis to ensure that the Best Available Control Technology (BACT) is used to limit emissions of regulated pollutants. Controls determined to meet BACT are imposed on a case-by-case basis, taking into account energy, environmental and economic costs, including the cost of controls. BACT analyses may also be required for estimating the cost/benefit ratios for proposed broad-scale regulatory management strategies for reducing emissions within an industrial category or across many categories. Knowledge of the estimated costs allows a facility to plan its financial future or a government agency to plan future control policy options.