Fuels

Fuels are materials that release energy when they undergo chemical or nuclear reactions, and are used to produce heat, light, motion, or electricity. They can be solids, liquids, or gases and serve as energy carriers in many applications.

Fossil fuels—coal, oil, and natural gas—are the largest historic sources of energy. Biofuels, produced from contemporary or waste biomass, provide renewable alternatives. Nuclear fuels, primarily uranium and plutonium in reactors, provide energy through fission. Synthetic fuels, including methanol and fuels produced from captured carbon dioxide and hydrogen, aim to be compatible with existing engines.

Energy content varies by fuel and form. For example, hydrocarbon fuels have high energy density by mass or volume, supporting transport and power generation. Efficiency depends on technology (internal combustion engines, gas turbines, boilers, fuel cells) and operating conditions.

Environmental considerations include greenhouse gas emissions, air pollutants, and lifecycle impacts. Safety concerns cover flammability, explosion risk, and storage requirements. Supply chains involve extraction, processing, distribution, and regulation.

Future developments focus on reducing emissions through electrification, renewable fuels, hydrogen, and carbon-neutral synthetic fuels, as well as improving efficiency and resource use. The term "fuel" is often broadened to include energy carriers that enable energy services across sectors.