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Duke Energy is one of the largest US utilities, with regulated utilities in the Carolinas, Indiana, Florida, Ohio, and Kentucky that deliver electricity to more than 8 million customers. Its natural gas utilities serve more than 1.6 million customers.

Xcel Energy manages utilities serving 3.9 million electric customers and 2.2 million natural gas customers in eight states. Its utilities are Northern States Power, which serves customers in Minnesota, North Dakota, South Dakota, Wisconsin, and Michigan; Public Service Company of Colorado; and Southwestern Public Service Company, which serves customers in Texas and New Mexico. It is one of the largest renewable energy suppliers in the US, with more than half of its electricity sales coming from carbon-free energy.

Alliant Energy is the parent of two regulated utilities, Interstate Power and Light and Wisconsin Power and Light. Together, IPL and WPL serve nearly 1 million electric customers and 425,000 natural gas-only customers. Both subsidiaries engage in the generation and distribution of electricity and the distribution and transportation of natural gas. Alliant also owns a 16% interest in American Transmission Co.

American Electric Power is one of the largest regulated utilities in the United States, providing electricity generation, transmission, and distribution to more than 5 million customers in 11 states. About 42% of AEP's capacity is coal, with the remainder from a mix of natural gas (27%), renewable energy and hydro (21%), nuclear (8%), and demand response (2%). Vertically integrated utilities, transmission and distribution, and generation and marketing support earnings.