local ownership of all utilities, this portion of the territory is operated as a separate subsidiary: Northern States Power-Wisconsin. To power this vast territory, the company built numerous power plants, many of which have long since been retired and decommissioned. Some capacity was extended withtransmission lines and substations. The currently operational nuclear power plants are Prairie Island (1974), and Monticello Nuclear Generating Plant (1971). Sherburne County Generating Station (Sherco) and Allen S. King in Bayport are the last to be fueled by coal. Three other coal-fired plants, Riverside, High Bridge, and Black Dog, have been retrofitted to run on natural gas. By 1986, the company had grown to be included among the S&P 500 list of 500 of the largest companies in the United States. By that time it had accumulated nearly $1.2 billion in long-term debt. NSP served the agriculturally based region of its headquarters state of Minnesota, and also the neighboring states of North Dakota and South Dakota to the west. These territories were served through its subsidiary, NSP-Minnesota. Primergy merger On May 3, 1995, Northern States Power Company and Wisconsin Energy Corporation () each filed a Securities and Exchange Commission Form 8-K to combine in a merger-of-equals transaction to form Primergy Corporation, which would be a registered public utility holding company, and to be the new parent of both NSP and of the operating subsidiaries of WEC. It would be the tenth largest investor-owned electric and gas utility company in the United States, based on market capitalization at that time of about US$6.0 billion, and with 1994 combined revenues of US$4.2 billion and with total assets of more than US$10.0 billion. Shareholders of NSP common stock would own 1.626 shares of stock of Primergy for each share of NSP stock they owned, and WEC shareholders were to receive one-for-one shares of Primergy. At that time, Richard A. Abdoo, served as chairman, president and chief executive officer of Wisconsin Energy. James J. Howard served in the same positions with Northern States Power. With the new Primergy Corporation, Howard would become chairman and CEO, and Abdoo would serve as vice chairman, president and chief operating officer. Further, with Howard scheduled to retire in July 2000, Abdoo would then succeed him as chairman of Primergy. Wisconsin Energy's two then-existing utility subsidiaries, Wisconsin Electric Power Company (WEPCO) and Wisconsin Natural Gas Company (WNG) were to be consolidated under a new subsidiary