A fuel is a substance that is changed in some way to produce heat, electricity, or other forms of energy. This is usually by being burnt in fire, although there are exceptions, such as nuclear fuel. Fuel can be divided into two main types: fossil fuels and other fuels.

There are several kinds of fossil fuels:

• coal
• oil and products that are refined from oil (gasoline, diesel, kerosene)
• natural gas

Some people do not want us to use fossil fuels because they may pollute the environment. Because all fossil fuels are made out of carbon, burning them makes carbon dioxide. Some people think that too much carbon dioxide in the air may cause a greenhouse effect. Fossil fuels are also non-renewable, or renew extremely slowly (thousands of years). This means that we will eventually run out of fossil fuels.

Other fuels are not made from fossils. Some of these, like nuclear and hydrogen, do not have carbon in them. Others, like wood or ethanol, do have carbon in them. Some examples of these fuels are:

• Nuclear fuel (uranium, plutonium, thorium, etc.)
• Hydrogen
• Extracted from the wind
• Biofuels from biomass
  • Firewood
  • Biodiesel (a diesel-type fuel made from plants)
  • Ethanol (made from grains or other plants)

These fuels are renewable. This means that we can make more of them if we run out. For instance, if we run out of ethanol, we can grow some more corn and make some more ethanol.

Wikimedia Commons has media related to Fuel.

• Fuel -Citizendium