Currently petroleum furnishes about 40 percent of the commercial energy used for transportation and heating. Coal provides about 26 percent of all the commercial energy used in the world, and is used mainly to produce steam for generators and steam engines and turbines. Natural gas accounts for about 21 percent of the energy used in the world. The most widespread use of natural gas is to generate steam for electric power or steam engines, to heat buildings, to cook with and other uses in various household appliances.

Most petroleum is removed from the earth as a liquid called crude oil. Coal is mined from the Earth, which is a dangerous process that can cause respiratory diseases in miners. Natural gas comes from deposits in the earth also. Natural gas is a clean source of energy and requires no further refining once mined from the Earth. Burning fossil fuel produces CO₂and other atmospheric pollutants such as sulfur. In an effort to reduce atmospheric pollutants many companies have installed filters and other cleaning devices at factories utilizing fossil fuel. LEARN MORE

Water or hydropower, makes up around 7 percent of the world's commercial energy. Most water power is used to generate electric power. Since water power supplies energy without pollution and without using up the water in the process, it is widely thought to be the best source of power, however, the dams used to produce this power cause irreversible damage to the surrounding ecosystems both up and down stream, threatening and possibly eradicating plant and animal species. Nuclear energy provides another 6 percent of our energy. LEARN MORE

Nuclear fission produces vast amounts of energy from small amounts of fuel, the fission of 1 pound of uranium releases more energy than the burning of 3 million pounds (1,500 tons) of coal. Fission is the process of splitting atomic nuclei of certain elements such as uranium. This process produces hot waste water that may damage the environment and also produces waste that must be isolated to protect the environment. To reduce the thermal pollution, most new nuclear power plants have large water cooling devices. Currently scientists and engineers are working on experimental breeder reactors, basically stated, a much more efficient version of a fission reactor because it "breeds" new fuel while consuming the old fuel.

Nuclear fusion produces the same heat and light as our Sun. Scientists and engineers are working on ways to control nuclear fusion reactions, but unfortunately have not yet been able to efficiently produce usable amounts of energy. Since fusion devices use forms of hydrogen known as deuterium and tritium for their fuel, and hydrogen is found in large quantities in the world's oceans, fusion could provide a virtually unlimited source of fuel. LEARN MORE

Wood was once the main source of power for heat, and in many developing countries, wood is still the main source of heat energy. Most people in developed countries use wood only for aesthetic purposes or secondary heating, limited mainly to fireplaces and decorative woodstoves.