We study the drivers of the adoption of electricity generation technologies between 1970 and 2014 in the lower 48 U.S. states. Since the 1990s, major electricity market restructuring took place in some parts of the United States. We explore the implications of changing from a regulated “cost-of-service” or rate of return system to a partly and fully deregulated market on technology and fuel choices. We find that electricity market deregulation resulted in significant immediate investment in various natural gas technologies, and a reduction in coal investments. However, market deregulation impacted less negatively on high efficiency coal technologies. In states that adopted wholesale electricity markets, high natural gas prices resulted in more investment in coal and renewable technologies.