page_title: Fossil fuel
section_title: Reserves
hierarchical_section_title: Fossil fuel / Importance / Reserves
caption_attribution_description: Offshore platform located in the Gulf of Mexico, port location Cd. Del Carmen.
context_page_description: A fossil fuel is a fuel formed by natural processes, such as anaerobic decomposition of buried dead organisms, containing organic molecules originating in ancient photosynthesis that release energy in combustion.
  Such organisms and their resulting fossil fuels typically have an age of millions of years, and sometimes more than 650 million years.
  Fossil fuels contain high percentages of carbon and include petroleum, coal, and natural gas. Peat is also sometimes considered a fossil fuel.
  Commonly used derivatives of fossil fuels include kerosene and propane.
  Fossil fuels range from volatile materials with low carbon-to-hydrogen ratios, to liquids, to nonvolatile materials composed of almost pure carbon, like anthracite coal.
  Methane can be found in hydrocarbon fields alone, associated with oil, or in the form of methane clathrates.
  As of 2018, the world's main primary energy sources consisted of petroleum, coal, and natural gas, amounting to an 85% share for fossil fuels in primary energy consumption in the world.
  Non-fossil sources included nuclear, hydroelectric, and other renewables.
  The share of renewables in the world's total final energy consumption was 18% in 2018.
context_section_description: Levels of primary energy sources are the reserves in the ground. Flows are production of fossil fuels from these reserves. The most important primary energy sources are carbon-based fossil energy sources.
caption: An oil well in the Gulf of Mexico
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