American Electric Power Company, Inc. (AEP), (railcar reporting mark: AEPX) is a major investor-owned electric utility in the United States, delivering electricity to more than five 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 network that includes 765 kilovolt ultra-high voltage transmission lines, more than all other U.S. transmission systems combined. AEP's transmission system directly or indirectly serves about 10 percent of the electricity demand in the Eastern Interconnection, the interconnected transmission system that covers 38 eastern and central U.S. states and eastern Canada, and approximately 11 percent of the electricity demand in the Electric Reliability Council of Texas, the transmission system that covers much of Texas. AEP's utility units operate as AEP Ohio, AEP Texas, Appalachian Power (in Virginia, West Virginia, and Tennessee), Indiana Michigan Power, Kentucky Power, Public Service Company of Oklahoma, and Southwestern Electric Power Company (in Arkansas, Louisiana and east Texas). AEP's headquarters are in Columbus, Ohio. American Electric Power was the first utility to utilize 345 kV transmission lines which took place in 1953. The company ranked 185th on the 2018 Fortune 500 of the largest United States corporations by revenue. Subsidiaries The company is divided into seven major geographic local operating companies: AEP Ohio AEP Ohio serves 1.5 million customers in central, southern and northwestern Ohio. For years, it consisted of two operating companies, Ohio Power and Columbus Southern Power. However, in 2014, Columbus Southern was merged into Ohio Power, leaving Ohio Power as the legal operating company for regulatory purposes. AEP Texas AEP Texas was formed from a merger of various predecessor utilities, and joined AEP as part of its acquisition of Central and South West Corporation in 1997. It consists of AEP Texas North Company (formerly West Texas Utilities), which operates in west Texas, and AEP Texas Central Company (formerly Central Power and Light), which operates in south Texas. Appalachian Power Appalachian Power (APCO) is based in Charleston, West Virginia and owns the naming rights to Appalachian Power Park in Charleston. APCO serves about one million customers in central and Southern West Virginia, the West Virginia Panhandle, Southwest Virginia and parts of Northeast Tennessee, specifically Kingsport. Cities in the Appalachian Power service territory include Wheeling, Charleston and Huntington, West Virginia; Roanoke, Virginia and Kingsport. Until