To a certain extent wood, solar, wind, tidal, chemical, and geothermal sources also provide energy. 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 CO 2 and 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.