Over 85% of the energy used in the world is from non-renewable supplies. Most developed nations are dependent on non-renewable energy sources. Industrialized societies depend on non-renewable energy sources. Fossil fuels are the most commonly used types of non-renewable energy.Coal is the most abundant fossil fuel in the world with an estimated reserve of one trillion metric tons.Most of the world's coal reserves exist in Eastern Europe and Asia, but the United States also has considerable reserves. Coal formed slowly over millions of years from the buried remains of ancient swamp plants. Crude oil or liquid petroleum is a fossil fuel that is refined into many different energy products (e.g., gasoline, diesel fuel, jet fuel,heating oil). Oil forms underground in rock such as shale, which is rich inorganic materials. Natural gas production is often a by-product of oil recovery, as the two commonly share underground reservoirs. Natural gas is a mixture of gases, the most common being methane (CH4). Oil shale and tar sands are the least utilized fossil fuel sources. Oil shale is sedimentary rock with very fine pores that contain kerosene, a carbon-based,waxy substance. In most electric power plants, water is heated and converted into steam, which drives a turbine-generator to produce electricity. Fossil-fueled power plants produce heat by burning coal, oil, or natural gas. In a nuclear power plant, the fission of uranium atoms in the reactor provides the heat to produce steam for generating electricity.