Biofuels contain carbon and although they may burn “cleaner” than oil-derived fuels, they do not avoid generating carbon dioxide emissions.

Consuming the largest amount of energy, space heating accounts for 31% of all residential energy used. Space cooling accounts for an additional 12% of energy usage.

Consuming the largest amount of energy, space heating accounts for 31% of all residential energy used. Space cooling accounts for an additional 12% of energy usage.

Consuming the largest amount of energy, space heating accounts for 31% of all residential energy used. Space cooling accounts for an additional 12% of energy usage.

In 2008, wind accounted for 0.5% of America's energy portfolio.

In 2008, wind accounted for 0.5% of America's energy portfolio.

In 2005, a million Btu of energy from coal cost approximately $2, versus $5 for natural gas and $10 for oil. However, prices can fluctuate due to changes in the economy and new government policies.

In 2005, a million Btu of energy from coal cost approximately $2, versus $5 for natural gas and $10 for oil. However, prices can fluctuate due to changes in the economy and new government policies.

Less than 2% of the U.S. supply of natural gas is imported from outside North America.

Less than 2% of the U.S. supply of natural gas is imported from outside North America.

A gallon of gasoline contains about the same energy as 1 kg of hydrogen. Although fuel cells are expected to be twice as efficient as gasoline vehicles, hydrogen is very diffuse and storing an ample supply on board represents an engineering challenge.

A gallon of gasoline contains about the same energy as 1 kg of hydrogen. Although fuel cells are expected to be twice as efficient as gasoline vehicles, hydrogen is very diffuse and storing an ample supply on board represents an engineering challenge.

Tidal energy is gravitational in origin. Solar energy comes from nuclear reactions in the sun.

Tidal energy is gravitational in origin. Geothermal energy comes from radioactive decay inside the earth.

Tidal energy is gravitational in origin. Solar energy comes from nuclear reactions in the sun, and geothermal energy comes from radioactive decay inside the earth.

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.

U.S. domestic production of crude oil peaked around 1970 at about 9.5 million barrels per day (MBD) and declined to about 5.1 MBD by 2006.