This paper examines changes in the utilization rates (annual capacity factors) of coal-burning power plants in the eastern United States after 1996, when federal regulators opened the transmission system to wholesale power markets. This and other accompanying market-oriented reforms were intended to improve efficiency by encouraging regional dispatch by independent system operators. If the reforms made dispatch more efficient, then utilization rates of high-cost plants should have fallen relative to those of low-cost plants since 1996. A difference-in-difference model using plant-level panel data indicates that relative utilization rates of high-cost plants did indeed fall after 1996, but only in regions with independent system operators. Simulations indicate cost savings on the order of two to three percent.