Due to its relatively low cost and abundance, coal is used to generate about half of the electricity consumed in the United States. Coal is the largest domestically-produced source of energy. Coal use, however, results in higher amounts of carbon dioxide per unit of energy than the use of oil or natural gas.

A cap-and-trade program is designed to reduce emissions of a pollutant by placing a limit (or cap) on the total amount of emissions. The cap is implemented through a system of allowances that can be traded to minimize costs to affected sources. Cap-and-trade programs for greenhouse gas emissions would increase the costs of using fossil fuels.

There are currently 104 commercial nuclear reactors at 65 nuclear power plants in 31 States. Since 1990, the share of the Nation's total electricity supply provided by nuclear power generation has averaged about 20%, with the level of nuclear generation growing at roughly the same rate as overall electricity use. Between 1985 and 1996, 34 new reactors were placed in service. In addition, nuclear generation has increased as a result of higher utilization of existing capacity and from technical modifications to increase nuclear plant capacity (expressed in megawatts). In response to incentives provided by the Energy Policy Act of 2005, nuclear power output is expected to grow, but at a slightly lower rate than total electricity generation.

To compare or aggregate energy consumption across different energy sources like oil, natural gas, and electricity, we must use a common unit of measure. This is similar to calculating your food energy intake by adding up the calories in whatever you eat.

On an annual basis from 2003 to 2008, the United States imported between 13% and 16% of its natural gas requirements. Most of these imports were in gaseous form delivered by pipeline from Canada. However, natural gas imports have also come in liquid form from overseas. Between 1% and 3% of U.S. demand for natural gas was met by LNG from 2003 to 2008.

The United States imported about 57% of the petroleum,1 which includes crude oil and refined petroleum products, that we consumed during 2008. Nearly half of these imports came from the Western Hemisphere. Our dependence on foreign petroleum is expected to decline in the next two decades.

The major energy sources in the United States are petroleum (oil), natural gas, coal, nuclear, and renewable energy. The major users are residential and commercial buildings, industry, transportation, and electric power generation. The pattern of fuel use varies widely by sector. For example, oil provides 95% of the energy used for transportation, but only 1% of the energy used to generate electric power. Understanding the relationships between the different energy sources and their uses provides insights into many important energy issues.

Americans used renewable energy sources — water (hydroelectric), geothermal, wind, sun (solar), and biomass — to meet about 7% of our total energy needs in 2008.

Renewable portfolio standards are policies designed to increase electricity generation from renewable resources, including wind, solar, geothermal, and biomass. Many States have their own renewable portfolio standards, although currently there is no program at the National level. States with renewable portfolio programs have seen an increase in the amount of electricity generated from renewable fuels.