A number of U.S. states have passed legislation targeting energy efficiency and peak demand reduction. We study one such state, Pennsylvania, within the context of RIM, a regional electricity market covering numerous different states. Our focus is on the distributive impacts of this policy-specifically how the policy is likely to impact electricity prices in different areas of Pennsylvania and in the PJM market more generally. Such spatial differences in policy impacts are difficult to model and the transmission system is often ignored in policy studies. Our model estimates supply curves on a "zonal" basis within regional electricity markets and yields information on price and fuel utilization within each zone. We use the zonal supply curves estimated by our model to study regional impacts of energy-efficiency legislation on utilities both inside and outside of Pennsylvania. For most utilities in Pennsylvania, it would reduce the influence of natural gas on electricity price formation and increase the influence of coal. It would also save 2.1 to 2.8 percent of total energy cost in Pennsylvania in a year similar to 2009. The savings are lower than 0.5 percent in other PJM states and the prices may slightly increase in Washington, DC area. (C) 2012 Elsevier Ltd. All rights reserved.