The British Thermal Unit, or Btu, is frequently used as a measure for energy content of fuels. One gallon of gasoline contains about 124,000 Btu.

The British Thermal Unit, or Btu, is frequently used as a measure for energy content of fuels. One gallon of gasoline contains about 124,000 Btu.

The British Thermal Unit, or Btu, is frequently used as a measure for energy content of fuels. One gallon of gasoline contains about 124,000 Btu.

With less than 5% of the world's population, the United States is home to one-third of the world's automobiles.

With less than 5% of the world's population, the United States is home to one-third of the world's automobiles.

Oil, biofuels, natural gas, and coal are all used to generate electricity in the United States.

Oil, biofuels, natural gas, and coal are all used to generate electricity in the United States.

Oil, biofuels, natural gas, and coal are all used to generate electricity in the United States.

Oil, biofuels, natural gas, and coal are all used to generate electricity in the United States.

The United States and Canada are both developed countries. China and India are projected to have the greatest growth in energy consumption between 2006 and 2030.

The United States and Canada are both developed countries. China and India are projected to have the greatest growth in energy consumption between 2006 and 2030.

U.S. consumption of energy sources is projected to rise by 13% between now and 2030.

U.S. consumption of energy sources is projected to rise by 13% between now and 2030.

In the United States, the transportation sector releases the most CO2. In 2006, the transportation sector released nearly 2 billion metric tons of carbon dioxide, nearly all of which was from oil.

In the United States, the transportation sector releases the most CO2. In 2006, the transportation sector released nearly 2 billion metric tons of carbon dioxide, nearly all of which was from oil.

In the United States, the transportation sector releases the most CO2. In 2006, the transportation sector released nearly 2 billion metric tons of carbon dioxide, nearly all of which was from oil.

Nuclear power accounted for 9% of the U.S. energy supply in 2008.

Nuclear power accounted for 9% of the U.S. energy supply in 2008.

Electricity is a secondary energy source because it can only be produced from the use of primary energy sources such as coal, natural gas, or nuclear reactions.

Electricity is a secondary energy source because it can only be produced from the use of primary energy sources such as coal, natural gas, or nuclear reactions.

Electricity is a secondary energy source because it can only be produced from the use of primary energy sources such as coal, natural gas, or nuclear reactions.

Electricity is a secondary energy source because it can only be produced from the use of primary energy sources such as coal, natural gas, or nuclear reactions.

Mining coal disturbs the land and modifies the chemistry of rainwater runoff, which in turn affects stream and river water quality.