The purpose of this publication is to provide year-end statistics about electric generating units operated by electric utilities in the United States (the 50 States and the District of Columbia). The publication also provides a 10-year outlook of future generating unit additions. The Summary Statistics chapter contains aggregate capacity statistics at the national and various regional levels for operable electric generating units and planned electric generating unit additions. Aggregate capacity data at the national level are presented by energy source and by prime mover. Aggregate capacity data at the various regional levels are presented by prime energy source. Planned capacity additions in new units are summarized by year, 1991 through 2000. Additionally, this chapter contains a summary of electric generating unit retirements, by energy source and year, from 1991 through 2000. The chapter on Operable Electric Generating Units contains data about each operable electric generating unit and each electric generating unit that was retired from service during the year. Additionally, it contains a summary by energy source of electric generating unit capacity additions and retirements during 1990. Finally, the chapter on Projected Electric Generating Unit Additions contains data about each electric generating unit scheduled by electric utilities to start operation between 1991 and 2000. 11 figs., 22 tabs.