Aviation fuel is a specially refined petroleum product designed to power aircraft engines. It comes in two main categories: jet fuel for turbine engines (the kind in commercial airliners and military jets) and avgas for piston engines (the kind in smaller propeller-driven planes). Both are engineered to perform reliably at extreme altitudes and temperatures, which is what separates them from the gasoline or diesel you’d put in a car.
Jet Fuel: The Standard for Commercial Aviation
The jet fuel powering commercial flights is a refined kerosene. It’s lighter than diesel but heavier than gasoline, and it burns efficiently in the turbine engines that drive everything from regional jets to wide-body airliners. Two grades dominate the market: Jet A and Jet A-1.
Jet A is primarily used in the United States. It has a freezing point of -40°C (-40°F). Jet A-1 is the standard everywhere else in the world and has a lower freezing point of -47°C (-52.6°F), making it better suited for long international routes that cross polar regions or fly at very high altitudes where temperatures can plunge below -50°C. In practice, the two fuels are nearly identical in how they burn and how much energy they deliver. The freezing point is the key distinction.
Jet fuel packs a lot of energy into a relatively small weight. Its heat of combustion sits around 43.3 megajoules per kilogram, which is roughly comparable to gasoline by weight. That energy density is critical in aviation, where every kilogram matters. A fuel that delivered less energy per unit of weight would force planes to carry more of it, cutting into the payload of passengers and cargo they could transport.
Avgas: Fuel for Piston-Engine Aircraft
Smaller propeller planes, the kind used for flight training, crop dusting, private travel, and aerial surveying, run on aviation gasoline, or avgas. Nearly all avgas sold today is a single grade called 100LL (100 low lead). The “100” refers to its motor octane number, a measure of the fuel’s resistance to premature ignition inside the engine. The “LL” means it contains a reduced amount of tetraethyl lead, a chemical additive that raises the octane rating.
High-octane fuel matters because many piston aircraft engines have high compression ratios. If the fuel ignites too early, before the spark plug fires, it creates uncontrolled detonation that can destroy pistons and other internal components, potentially causing engine failure in flight. Lead is what prevents this. About 167,000 aircraft in the United States, and roughly 230,000 worldwide, depend on 100LL avgas for safe operation.
The lead content is the most controversial aspect of avgas. Leaded automotive gasoline was phased out decades ago, but aviation held onto it because no approved unleaded alternative could safely meet the octane needs of every piston engine in service. That is now changing, with unleaded avgas formulations working through the certification process.
What Gets Added Before It Reaches the Plane
Raw refined fuel isn’t quite ready for an aircraft tank. Several additives are blended in to handle the specific hazards of flight. Fuel system icing inhibitors prevent ice crystals from forming as temperatures drop at altitude. Without them, ice can block fuel lines and starve the engine. Static dissipator additives reduce the buildup of static electricity during fueling and flight, lowering the risk of sparks. Corrosion inhibitors protect the metal components of fuel tanks and delivery systems.
These additives are standardized and coded so that ground crews at any airport in the world know exactly what’s in the fuel they’re pumping. An “A++” code, for example, indicates Jet A kerosene with icing inhibitor, corrosion inhibitor, and static dissipator included.
How Aviation Fuel Affects the Environment
Burning 1 kilogram of jet fuel produces 3.16 kilograms of carbon dioxide. The CO2 output exceeds the fuel weight because during combustion, each carbon atom in the fuel bonds with two oxygen atoms pulled from the surrounding air, creating a heavier molecule. For context, a single transatlantic flight on a large airliner can burn tens of thousands of kilograms of fuel.
Avgas adds a separate concern: lead emissions. Piston-engine aircraft are now the largest remaining source of lead released into the air in the United States. While the total volume of avgas burned is small compared to jet fuel, the lead it contains accumulates in soil and air near airports, particularly affecting communities in the immediate vicinity.
Sustainable Aviation Fuel
Sustainable aviation fuel, or SAF, is a broad term for jet fuel produced from non-petroleum sources like used cooking oil, agricultural waste, municipal solid waste, or even captured CO2. The goal is a fuel that works in existing engines and existing airport infrastructure without modification, just with a smaller carbon footprint across its full lifecycle.
Current regulations allow SAF to be blended with conventional jet fuel at levels up to 50%, depending on how the fuel was produced. Several production pathways have been approved, including processes that convert plant-based oils into a synthetic kerosene and others that use a chemical process similar to the one that turns coal or natural gas into liquid fuel. All of them must meet the same performance specifications as conventional Jet A or Jet A-1.
The 50% blending cap exists because SAF and petroleum jet fuel have slightly different molecular profiles. Blending ensures the final product stays within the tight specification window that engines and fuel systems are certified to handle. Some producers are working toward 100% SAF approval, but the certification process is rigorous and slow by design, since the consequences of a fuel failure at 35,000 feet are catastrophic.
Why You Can’t Just Use Car Gasoline
Automotive gasoline and aviation fuel might both start as crude oil, but they’re refined and tested to very different standards. Jet fuel needs to remain liquid at temperatures that would turn car gasoline into a slushy mess. Avgas needs an octane rating that regular pump gas can’t reach. Both aviation fuels undergo batch-by-batch quality testing that car fuel does not, because an engine stall on a highway is an inconvenience while an engine failure at altitude is a potential disaster.
The volatility profile also differs. Car gasoline is designed to vaporize easily for quick cold starts in a ground-level engine. Jet fuel is formulated to resist vaporizing at the low pressures found at high altitude, where premature vaporization could create air bubbles in fuel lines and interrupt flow to the engines. Every property of aviation fuel, from its freezing point to its flash point to its energy content, is tuned for the specific demands of flight.