This paper reports on four areas of research concerning Title IV of the 1990 Clean Air Act Amendments that regulates emissions of SO2 from electricity generation. The first is the costs of the program over the long-run as estimated from the current perspective taking into account recent changes in fuel markets and technology. We compare projected costs with potential cost savings that can be attributable to formal trading of emission allowances. The second area is an evaluation of how well allowance trading has worked to date. The third area is the relationship between compliance costs and economic costs from a general equilibrium perspective. The fourth area is a comparison of benefits and costs for the program.