American Electric Power (AEP) is a major investor-owned electric utility in the United States, delivering electricity to more than 5 million customers in 11 states.AEP ranks among the nation's largest generators of electricity, owning nearly 38,000 megawatts of generating capacity in the U.S. AEP also owns the nation's largest electricity transmission system, a nearly 39,000-mile (63,000 km)-network that includes 765 kilovolt ultra-high voltage transmission lines, more than all other U.S.