Coal is used almost entirely for electricity generation, nuclear and hydropower completely so. Renewable sources (except hydropower) continue to offer more potential than actual energy production, although fuel ethanol has become a significant factor as a transportation fuel. Wind power also has recently grown rapidly, although it still contributes only a small share of total electricity generation. Conservation and energy efficiency have shown significant gains over the past three decades, and offer encouraging potential to relieve some of the dependence on imports that has caused economic difficulties in the past as well as the present. The historical trends show that petroleum has been and continues to be the major source of energy, rising from about 38% in 1950 to 45% in 1975, then declining to about 40% in response to the energy crisis of the 1970s. Natural gas followed a similar pattern at a lower level, increasing its share of total energy from about 17% in 1950 to over 30% in 1970, then declining to about 25% in 1995. Consumption of coal in 1950 was 35% of the total, almost equal to oil, but it declined to about 20% a decade later. Oil

About 40% of the energy consumed in the United States is supplied by petroleum, and that proportion remained approximately the same since 1950, although in recent years it has declined to about 36%. Also unchanged is the almost total dependence of the transportation sector on petroleum, mostly gasoline. In more recent years, successful extraction of tight oil (also called "shale oil") in the United States has added significantly to world resources estimates. Utilities found themselves committed to increasing dependence on oil just at the time of shortages and high prices; in 1975 almost 9% of oil consumption went for power production. While petroleum consumption increased throughout the period from 1950 to the present (except for a temporary decline following the price surge of the 1970s and another in 2009), U.S. domestic production peaked in 1970. Diesel fuel consumption showed a similar dramatic increase. This run-up of oil prices was unlike the two oil crises in the 1970s, in that there was no major interruption of supply. Numerous factors in addition to the current cost of production contribute to the price of oil. Electricity

While overall energy consumption in the United States increased nearly three-fold since 1950, electricity consumption increased even more rapidly. In addition, federal energy policy viewed generation of electricity by gas to be a wasteful use of a diminishing resource. Nuclear power started coming on line in significant amounts in the late 1960s, and by 1975, in the midst of the oil crisis, was supplying 9% of total generation. However, increases in capital costs, construction delays, and public opposition to nuclear power following the Three Mile Island accident in 1979 curtailed expansion of the technology, and many construction projects were cancelled. Continuation of some construction increased the nuclear share of generation to 20% in 1990, where it remains currently. Construction of major hydroelectric projects has also essentially ceased, and hydropower's share of electricity generation has gradually declined from 30% in 1950 to 15% in 1975 and less than 10% in 2000. However, hydropower remains highly important on a regional basis. The recent boom in production of shale gas has led to an oversupply and consequently lower prices.
Energy policy has been a recurring issue for Congress since the first major crises in the 1970s. As an aid in policymaking, this report presents a current and historical view of the supply and consumption of various forms of energy.
The historical trends show petroleum as the major source of primary energy, rising from about 38% in 1950 to 45% in 1975, and then declining to about 40% in response to the energy crises of the 1970s. Significantly, the transportation sector continues to be almost completely dependent on petroleum, mostly gasoline. Oil prices, which had been low and stable throughout the 1990s, resumed the volatility they had shown in the 1970s and early 1980s. Starting in 2004, perceptions of impending inability of the industry to meet increasing world demand led to rapid increases in the prices of oil and gasoline. The continuing high prices stimulated development of non-conventional oil resources, first in Canadian oil sands, then in the United States in shale deposits. U.S. oil production, which had apparently peaked, showed a dramatic increase starting in 2009. U.S. imports of oil have also been decreasing over the same time period, and there are calls to allow more exports.
Natural gas followed a long-term pattern of U.S. consumption similar to that of oil, at a lower level. Its share of total energy increased from about 17% in 1950 to more than 30% in 1970, then declined to about 20%. Recent developments of large deposits of shale gas in the United States have increased the outlook for U.S. natural gas supply and consumption in the near future, and imports have almost disappeared. The United States is projected to be a net natural gas exporter by 2018.
Consumption of coal in 1950 was 35% of total primary energy, almost equal to oil, but it declined to about 20% a decade later and has remained at about that proportion since then. Coal currently is used almost exclusively for electric power generation, and its contribution to increased production of carbon dioxide has made its use controversial in light of concerns about global climate change. U.S. coal exports have been on the rise in recent years.
Nuclear power started coming online in significant amounts in the late 1960s. By 1975, in the midst of the oil crisis, it was supplying 9% of total electricity generation. However, increases in capital costs, construction delays, and public opposition to nuclear power following the Three Mile Island accident in 1979 curtailed growth in generation facilities, and many construction projects were cancelled. Continuation of some construction increased the nuclear share of generation to 20% in 1990, where it remains currently. Licenses for a number of new nuclear units have been in the works for several years, and preliminary construction for a few units has begun, but the economic downturn has discouraged action on new construction.
Construction of major hydroelectric projects has also essentially ceased, and hydropower's share of electricity generation has gradually declined, from 30% in 1950 to 15% in 1975 and less than 10% in 2000. However, hydropower remains highly important on a regional basis.
Renewable energy sources (except hydropower) continue to offer more potential than actual energy production, although fuel ethanol has become a significant factor in transportation fuel. Wind power has recently grown rapidly, although it still contributes only a small percentage share of total electricity generation. Conservation and energy efficiency have shown significant gains over the past three decades and offer potential to relieve some of the dependence on oil imports and to hold down long-term growth in electric power demand.