The widespread transition from coal to natural gas for new generation is exemplified by the morphing fleets of some of the biggest U.S. generators. Figures show the amount of power generated by each company using coal (top) and natural gas (bottom). Sources: POWER, NextEra, Duke Energy, Tennessee Valley Authority (TVA), Southern Co., American Electric Power (AEP), Dominion, Energy Information Administration (EIA)

Sonal Patel is POWER’s senior writer.