History of Energy in the United States: 1635-2000
	Total Energy
	The United States has always been a resource-rich nation, but in 1776, the year the Nation declared its independence from Great Britain, nearly all energy was still supplied by muscle power and fuelwood. America's vast deposits of coal and petroleum lay untapped and mostly undiscovered, although small amounts of coal were used to make coke, vital for casting the cannon that helped win the war. Mills made use of waterpower, and of course the wind enabled transport by ship.
	Fuelwood use continued to expand in parallel with the Nation's economic growth, but chronic shortages of energy in general encouraged the search for other sources. During the first 30 years or so of the 19th century, coal began to be used in blast furnaces and in making coal-gas for illumination. Natural gas also found limited application in lighting during the period. Even electricity sought a niche; for example, experiments were conducted with battery-powered electric trains in the 1840s and 1850s. Still, muscle power remained an important source of energy for decades. Although a number of mechanical innovations appeared, including the cotton gin and the mechanical reaper, they had the effect of multiplying the productivity of human and animal muscle power rather than spurring the development of machine power. It was not until well after mid-century that the total work output from all types of engines exceeded that of work animals.
	The westward expansion helped change that. As railroads drove west to the plains and the mountains, they left behind the fuelwood so abundant along the eastern seaboard. Coal became more attractive, both because deposits were often found near the new railroad rights of way and because its higher energy content increased the range and load of steam trains. Demand for coal also rose because the railroads were laying thousands of miles of new track and the metals industry needed an economical source of coke to make iron and steel for the rails and spikes. The transportation and industrial sectors in general began to grow rapidly during the latter half of the century, and coal helped fuel their growth.
	Petroleum got its start as an illuminant and ingredient in patent medicines and did not catch on as a fuel for some time. At the end of World War I, coal still accounted for about 75 percent of U.S. total energy use. About the same time, the horse and mule population reached 26 million and then went into permanent decline. The beginning of the transition from muscle power was over.
	America's appetite for energy as it industrialized was prodigious, roughly quadrupling between 1880 and 1918. Coal fed much of this growth, while electricity expanded in applications and total use alike. Petroleum got major boosts with the discovery of Texas's vast Spindletop Oil Field in 1901 and with the advent of mass-produced automobiles, several million of which had been built by 1918.
	In the years after World War II, "Old King Coal" relinquished its place as the premier fuel in the United States. The railroads lost business to trucks that ran on gasoline and diesel fuel, and also began switching to diesel locomotives themselves. Labor troubles and safety standards drove up coal production costs. The declining demand for natural gas as an illuminant forced that industry to look for other markets, and because heating applications had obvious potential, natural gas replaced coal in many household ranges and furnaces. The coal industry survived, however, mainly because nationwide electrification created new demand for coal among electric utilities despite regional competition from hydroelectric and petroleum-fired generation.
	Most energy produced today in the United States, as in the rest of the industrialized world, comes from fossil fuels--coal, natural gas, crude oil, and natural gas plant liquids (Figure 2). Although U.S. energy production takes many forms, fossil fuels together far exceed all other sources of energy. In 2000 they accounted for 80 percent of total energy production and were valued at an estimated $148 billion (nominal dollars).
	Figure 2. Energy Production by Source for 2000
	(s)=less than 0.5 quadrillion Btu
	For much of its history, the United States was mostly self-sufficient in energy, although small amounts of coal were imported from Britain in colonial times. Through the late 1950s, production and consumption of energy were nearly in balance. Over the following decade, however, consumption slightly outpaced domestic production and by the early 1970s a more significant gap had developed (Figure 3).
	Figure 3. Energy Overview
	In 2000 the United States produced just under 72 quadrillion British thermal units (Btu) of energy and exported roughly 4 quadrillion Btu. Consumption totaled about 98 quadrillion Btu, requiring imports of almost 29 quadrillion Btu (Figure 4), 19 times the 1949 level.
	Figure 4. Energy Overview, 2000
	This appetite for imported energy is driven by petroleum consumption. U.S. petroleum imports in 1973 totaled 6.3 million barrels per day (3.2 million barrels per day of crude oil and 3.0 million barrels per day of petroleum products). In October 1973, however, the Arab members of the Organization of Petroleum Exporting Countries (OPEC) embargoed the sale of oil to the United States, prices rose sharply, and petroleum imports fell for two years (Figure 5). They increased again until the price of crude oil rose dramatically (roughly 1979 through 1981) and suppressed imports. The rising-import trend resumed by 1986 and, except for slight dips in 1990, 1991, and 1995, has continued ever since. In 2000 U.S. petroleum imports reached an annual record level of 11 million barrels per day.
	Figure 5. Petroleum Imports, 1960-2000
	The efficiency with which Americans use energy has improved over the years. One such measure is the amount of energy consumed to produce a (constant) dollar's worth of gross domestic product (GDP). By that yardstick, efficiency improved 49 percent between 1949 and 2000, as the amount of energy required to generate a dollar of output (chained 1996 dollars) fell from 20.6 thousand Btu to 10.6 thousand Btu. Nevertheless, a growing population and economy drove total energy use up. As the U.S. population expanded from 149 million people in 1949 to 281 million in 2000 (an increase of 89 percent), total energy consumption grew from 32 quadrillion Btu to 98 quadrillion Btu (up 208 percent). Per-capita energy consumption rose 63 percent, from 215 million Btu in 1949 to 350 million Btu in 2000.
	Energy plays a central role in the operation of the industrialized U.S. economy, and energy spending is commensurately large. In recent years, American consumers have spent over half a trillion dollars a year on energy. That energy is consumed in four broad sectors: residential, commercial, industrial, and transportation. Industry is historically the largest consuming sector of the economy. In contrast to the relatively smooth trends in the other sectors, industrial energy use has fluctuated sharply (Figure 6).
	Figure 6. Energy Consumption by End Use
	Sectoral energy sources have changed dramatically over time. In the residential and commercial sectors, for example, coal was the leading source as late as 1951 but then disappeared rapidly (Figure 7). Petroleum usage grew slowly to its peak in 1972 and then subsided. Natural gas became an important resource, growing strongly until 1972, when its growth essentially stalled. Electricity, only an incidental source in 1949, expanded in almost every year since then, as did the energy losses associated with producing and distributing the electricity. (See "Electricity" section below for an explanation of these losses.)
	Figure 7. Residential and Commercial Energy Consumption
	1Energy lost during generation, transmission, and distribution of electricity
	The expansion of electricity use reflects the increased electrification of U.S. households, which typically rely on a wide variety of electrical appliances and systems. In 1997, 99 percent of U.S. households had a color television and 47 percent had central air conditioning. Eighty-five percent of all households had one refrigerator; the remaining 15 percent had two or more. New products continued to penetrate the market; for example, in 1978 only 8 percent of U.S. households had a microwave oven, but by 1997 microwaves could be found in 83 percent. The U.S. Energy Information Administration (EIA) first collected household survey data on personal computers in 1990, when 16 percent of households owned one or more. By 1997 that share had more than doubled to 35 percent.
	U.S. home heating also underwent a big change. Over a third of all U.S. housing units were warmed by coal in 1950, but by 1999 that share was only 0.2 percent. Distillate fuel oil lost more than half its share of the home-heating market during the same period, falling from 22 percent to 10 percent. Natural gas and electricity gained as home-heating sources: the share of natural gas rose from about a quarter of all homes to over half, while electricity's share shot up from only 0.6 percent in 1950 to 30 percent in 1999. In recent times, electricity and natural gas have been the most common sources of energy used by commercial buildings as well.
	In the industrial sector, the consumption of both natural gas and petroleum rose steadily and in tandem until the oil embargo in 1973, after which their use fluctuated (Figure 8). Consumption of coal, once the leading source in the sector, shrank. Electricity and its associated losses grew steadily.
	Figure 8. Industrial Energy Consumption
	1Energy lost during generation, transmission, and distribution of electricity
	About three-fifths of the energy consumed in the industrial sector is used for manufacturing. The remainder goes to mining, construction, agriculture, fisheries, and forestry. Within manufacturing, large consumers of energy are the petroleum and coal products, chemicals and allied products, paper and allied products, and primary metal industries. Natural gas is the most commonly consumed energy source in manufacturing. The predominant end-use activity is process heating, followed by machine drive and then facility heating, ventilation, and air conditioning combined. About 7 percent of all energy consumed in the United States is used for nonfuel purposes, such as asphalt and road oil for roofing products and road building and conditioning; liquefied petroleum gases for feedstocks at petrochemical plants; waxes for packaging, cosmetics, pharmaceuticals, inks, and adhesives; and still gas for chemical and rubber manufacture.
	While variety and change in energy sources are the hallmarks of the industrial, residential, and commercial sectors, transportation has relied almost totally on petroleum since 1949 (Figure 9).
	Figure 9. Transportation Energy Consumption
	Compared with trends just prior to the oil embargo of 1973, fuel consumption per motor vehicle fell in the two decades that followed, miles traveled per vehicle generally fell until the early 1980s and then resumed a pattern of increase, and the fuel rate (i.e., miles per gallon) improved greatly before essentially leveling off in the 1990s (Figure 10).
	Figure 10. Motor Vehicle Indicators