Aviation fuel comes in two broad families: kerosene-based jet fuel for turbine engines and aviation gasoline (avgas) for piston engines. Within those families, several distinct grades exist, each defined by freezing points, octane ratings, or flash points tailored to specific aircraft and operating environments. Here’s what’s currently available and how they differ.
Jet Fuel Grades for Commercial Aviation
Nearly all commercial airliners and turbine-powered helicopters burn one of two kerosene-type fuels: Jet A-1 or Jet A. They’re chemically similar but differ in one critical specification: how cold they can get before they start to solidify.
Jet A-1 is the global standard. It has a maximum freezing point of minus 47°C and a minimum flash point (the temperature at which vapors can ignite near an open flame) of 38°C. Airlines flying long-haul polar routes or at very high altitudes rely on that low freezing point to keep fuel flowing through the engines in extreme cold. Jet A-1 is governed by ASTM D1655, the international specification for aviation turbine fuel.
Jet A is essentially the same kerosene but with a slightly higher freezing point ceiling of minus 40°C. That 7-degree difference makes it unsuitable for the coldest flight conditions, and in practice Jet A is produced and sold almost exclusively in the United States. Its flash point is the same 38°C minimum as Jet A-1. For domestic U.S. routes that don’t encounter extreme polar temperatures, it performs identically.
Military Jet Fuels: JP-5 and JP-8
Military operations add safety and performance demands that go beyond commercial specs, so the U.S. Department of Defense maintains its own fuel grades.
JP-8 is the military equivalent of Jet A-1. It shares the same 38°C minimum flash point but includes a mandatory corrosion inhibitor and an anti-icing additive not required in the commercial ASTM specification. A further variant called JP-8+100 contains a thermal stability additive that raises the fuel’s heat tolerance by about 56°C (100°F), helping it survive the extreme temperatures inside high-performance fighter jet fuel systems. That additive is not approved for commercial aircraft.
JP-5 is designed specifically for aircraft carrier operations, where fire safety around densely packed planes, munitions, and crew is paramount. Its minimum flash point is 60°C, a full 22 degrees higher than JP-8 or Jet A-1. That higher flash point means the fuel is much harder to ignite from a stray spark or shrapnel, making it significantly safer in confined naval environments. JP-5 also uses a narrower dosage range for its anti-icing additive (0.08 to 0.11% by volume) compared to JP-8 (0.07 to 0.10%).
Aviation Gasoline: 100LL
Piston-engine aircraft, which make up the bulk of the general aviation fleet, run on aviation gasoline rather than kerosene. Today, one grade dominates the market: 100LL, which stands for 100 octane, low lead. It is dyed blue for easy identification at the fuel pump.
Despite the “low lead” label, 100LL contains 0.56 grams of tetraethyl lead per liter. That lead is there to prevent engine knock (premature detonation) in the high-compression engines common in general aviation. Leaded automotive gasoline was banned decades ago, making avgas the last significant transportation fuel that still contains lead. Older grades like 80 octane (dyed red) and standard 100 octane (dyed green) have largely disappeared from the supply chain, though the FAA still lists 100 (green) in its fuel legends alongside 100LL (blue).
The Shift to Unleaded Avgas
The environmental and health concerns around leaded fuel have driven a push to replace 100LL entirely. The most advanced candidate is G100UL, produced by General Aviation Modifications Inc. (GAMI). The FAA has granted G100UL a Supplemental Type Certificate covering virtually every spark-ignition piston aircraft engine in its database. The fuel has already been produced at commercial scale, with over one million gallons manufactured and distributed through existing airport fueling infrastructure.
The transition isn’t completely seamless, though. In mid-2024, Cirrus Aircraft issued a service advisory noting that G100UL can degrade certain fuel tank sealants. Independent testing also found that standard nitrile rubber O-rings swelled beyond certified limits after several days of submersion in the unleaded fuel. GAMI recommends replacing nitrile components with silicone or fluoropolymer alternatives. The FAA’s broader unleaded transition plan also calls for intermixability testing between new unleaded fuels and legacy 100LL, since mixing is inevitable at airports during a gradual changeover. G100UL is already approved for co-mingling with 100LL and other gasolines rated at 100 motor octane number or below.
Sustainable Aviation Fuel for Turbine Engines
Sustainable aviation fuel, commonly called SAF, isn’t a separate grade in the traditional sense. It’s a kerosene-equivalent produced from non-petroleum sources (used cooking oil, agricultural waste, municipal solid waste, or synthesized from captured carbon dioxide and hydrogen). Once blended with conventional jet fuel and tested to ASTM D7566 standards, the resulting mixture meets the same ASTM D1655 specification as regular Jet A or Jet A-1.
Current rules allow SAF to make up a maximum of 50% of the blend for most approved production pathways. Some newer or less-proven pathways are capped at 10%. The blending limit exists to ensure compatibility with fuel systems and engines of all ages, since the global fleet includes aircraft spanning several decades of design. Once blended and certified, SAF-containing fuel is fully interchangeable with conventional jet fuel and requires no modifications to the aircraft.
How Fuel Grades Are Identified at the Airport
Color coding is the first line of defense against misfueling, which can be catastrophic. Avgas 100LL is dyed blue. The legacy 100 grade, where still encountered, is green. Jet fuel is typically clear to straw-colored. Fuel trucks, hoses, and nozzle fittings also differ by size and shape to make it physically difficult to pump jet fuel into a piston aircraft or vice versa.
Beyond the dye, each grade is defined by an ASTM specification number. Turbine fuels fall under ASTM D1655, and aviation gasolines fall under ASTM D910. These documents set the allowable ranges for dozens of properties including density, sulfur content, thermal stability, and the additive concentrations (like the anti-icing compound added at 0.07 to 0.15% by volume in commercial jet fuel) that keep the fuel safe across a wide envelope of temperatures and altitudes.