This article reconstructs the history of electric power uses in the US from 1900 to 1998 from a number of different sources of data. The uses are grouped into functional categories, viz. lighting, electrolysis, high temperature heat (electric furnace applications), low temperature heat (space heating and hot water), motor drive and electronics (radio, TV and information processing). Motor drive accounts for by far the largest absolute share of consumption, while low temperature heating is by far the most rapidly increasing application. We were able to subdivide motor drive into transportation applications (very important in the early years), air-conditioning and refrigeration, and 'other', but a further breakdown has not been possible, based on available data. The article also estimates the efficiency of conversion from electric power to 'secondary work' for each application, based on historical data (where available) and our estimates. Finally, we develop an estimate of the overall conversion efficiency of electricity to secondary work. Surprisingly, the overall efficiency has remained almost constant during the past century, even though all individual applications have become more efficient, because the least efficient applications (low temperature heat and fractional horsepower motors) have sharply increased their share. (C) 2004 Elsevier Ltd. All rights reserved.