What Is Jet Fuel Called? Jet A, Jet A-1, and More

The fuel that powers commercial airliners goes by a handful of specific names, the most common being Jet A and Jet A-1. These are kerosene-type fuels refined from petroleum, and while they sound nearly identical, the distinction between them matters for international operations and cold-weather flying. Beyond the commercial grades, military and specialty designations like JP-5, JP-8, and JP-7 exist to meet the demands of naval operations and supersonic flight. The naming system can seem arbitrary at first, but each label reflects a particular set of performance requirements that keeps aircraft safe across wildly different conditions.

Jet A and Jet A-1

Jet A is the standard commercial aviation fuel used almost exclusively within the United States. Jet A-1 is its international counterpart, used across Europe, Asia, and most of the rest of the world. Both are kerosene-based, and in everyday operation they perform so similarly that many pilots and passengers never think about the difference. The key distinction is the freezing point. Jet A is required to remain liquid down to −40 °C, while Jet A-1 must stay liquid down to −47 °C. That seven-degree gap sounds modest, but at cruise altitude where outside air temperatures can plunge below −50 °C, fuel that begins to gel or form wax crystals can block filters and starve engines. Long-haul international routes, particularly polar routes, are why Jet A-1’s tighter freezing spec exists.

Flash point is another property worth understanding. The flash point of jet fuel is essentially the lowest temperature at which the fuel gives off enough vapor to ignite if exposed to a spark or flame. For both Jet A and Jet A-1, this sits around 38 °C (100 °F), which is far higher than gasoline’s flash point of roughly −40 °C. That relatively high flash point is a deliberate safety feature: kerosene-type jet fuel is much harder to accidentally ignite during ground handling, fueling, and storage than gasoline would be.¹

A third grade, Jet B, is a wide-cut fuel blending kerosene with naphtha (a lighter petroleum fraction). Jet B ignites more easily and is more volatile, which makes it useful in extremely cold environments like northern Canada and parts of Alaska where conventional kerosene can be reluctant to vaporize. The trade-off is a lower flash point and greater fire risk on the ground, so Jet B sees limited use and is essentially a niche product.

Military Designations

The U.S. military uses its own naming system, prefixed “JP” for “Jet Propellant.” The number after JP is not a quality grade or octane-style rating; it simply identifies a specification that was developed at a particular time for a particular purpose.

JP-8 is the workhorse. It is the military’s standard fuel for nearly all fixed-wing aircraft, helicopters, and ground vehicles that run on turbine engines. Chemically, JP-8 is almost identical to Jet A-1. The difference lies in a package of additives the military mandates: corrosion inhibitors, anti-icing agents, thermal stability improvers, and static dissipater compounds. Research on JP-8 has found its baseline density sits around 797 kg/m³ and its ignition point at about 46 °C, with its freezing point measured well below −50 °C.² The additive package is what earns JP-8 its own designation rather than simply being called Jet A-1.

JP-5 is the U.S. Navy’s primary shipboard fuel. Aircraft carriers store enormous quantities of fuel in enclosed spaces with limited ventilation, so the Navy requires a fuel with a higher flash point than JP-8 (at least 60 °C versus about 38 °C). That extra thermal safety margin reduces the risk of fire during storage and fueling operations aboard ship. JP-5 is more expensive to refine because achieving that higher flash point means cutting out lighter, more volatile fractions of the kerosene blend.

JP-4 was the original wide-cut military fuel, similar to Jet B. The U.S. Air Force used it for decades, but its low flash point made it dangerously flammable during ground operations. After a series of fire-related accidents, the Air Force switched to JP-8 in the 1990s. JP-4 is essentially retired from mainstream use.

What Jet Fuel Is Made Of

All kerosene-type jet fuels share a broadly similar recipe. They are mixtures of hydrocarbons, mostly molecules with nine to sixteen carbon atoms strung together in chains or rings. Analyses of Jet A, Jet A-1, and JP-8 show that these fuels typically contain roughly 20% straight-chain alkanes, 40% branched (iso-) alkanes, 20% cycloalkanes, and 20% aromatics by volume.³ The straight-chain and branched alkanes contribute energy content and clean burning. The cycloalkanes improve density and thermal stability. The aromatics, while adding some energy density, are limited by specification because too high a concentration causes soot, smoke, and degradation of fuel-system seals.

This blend is not some exotic concoction. Kerosene-type jet fuel occupies a middle band in the crude oil distillation tower, heavier than gasoline and naphtha but lighter than diesel and heating oil. That positioning is why jet fuel smells somewhat like the kerosene in an old-fashioned lamp; they are close cousins. The refining process adjusts the proportions of each hydrocarbon class to meet the strict specifications the aviation industry demands.

Specifications and Who Sets Them

Jet fuel does not simply get refined and shipped. Every batch must meet published specifications before it is cleared for use. The major specifications governing global jet fuel quality include ASTM International D1655 (the primary civilian standard), the UK Ministry of Defence Standard 91-091 (widely used as the international benchmark), and the U.S. military’s MIL-DTL-83133 for JP-8 and MIL-DTL-5624 for JP-5.⁴ These documents define allowable ranges for density, viscosity, flash point, freezing point, sulfur content, aromatic content, and dozens of other properties.

The reason multiple spec systems exist is partly historical and partly practical. ASTM D1655 governs fuel produced and used in North America. Def Stan 91-091 harmonizes with D1655 but adds requirements relevant to European supply chains and extreme-cold operations. The military specs pile on additional additive mandates. In practice, a refinery aiming to sell fuel internationally will typically produce to the tightest overlapping requirements so the same batch can satisfy multiple customers. Airlines, airports, and fuel distributors run elaborate quality-control programs with sampling at every transfer point from refinery to wing tank.

Sustainable Aviation Fuel

Sustainable aviation fuel, or SAF, is a newer category that has been generating considerable industry attention. SAF is not a single product; it is an umbrella term for jet fuels produced from non-petroleum feedstocks like plant oils, agricultural waste, municipal solid waste, or even captured carbon dioxide. The end product must still meet the same performance specifications as conventional Jet A or Jet A-1, which means it has to be “drop-in” compatible with existing engines, fuel systems, and airport infrastructure.

The most common SAF pathway today produces a material called synthetic paraffinic kerosene, or SPK. Five different types of SPK have been certified under ASTM D7566 as blending components for conventional jet fuel. These include fuels produced through Fischer-Tropsch synthesis (FT-SPK), the alcohol-to-jet pathway (ATJ-SPK), hydroprocessed esters and fatty acids (HEFA-SPK), synthesized iso-paraffins from a sugar-to-jet pathway (SIP), and a Fischer-Tropsch variant with increased aromatic content (FT-SPK/A).⁵ Each uses a fundamentally different chemistry to arrive at a kerosene-range hydrocarbon blend.

Current regulations limit SAF to a maximum 50% blend with conventional petroleum-derived jet fuel for most pathways. The reason is that neat (100%) SPK fuels tend to lack aromatics, which conventional fuel-system seals have evolved to depend on for proper swelling and sealing. The Fischer-Tropsch pathway with added aromatics (FT-SPK/A) is one approach to producing a fully formulated fuel that could in principle qualify as Jet A-1 on its own without blending.⁶ Getting to 100% SAF across multiple pathways is a major research goal, but the certification process is slow and cautious by design since failure in aviation is unforgiving.

Why Energy Density Matters So Much for Aviation

One reason kerosene has remained aviation’s fuel of choice for decades is its energy density. A kilogram of Jet A packs roughly 43 megajoules of energy, and a liter holds about 34 megajoules. Both the energy per unit weight (gravimetric density) and the energy per unit volume (volumetric density) matter for aircraft design, because planes have limited space and limited weight capacity. A fuel that stores a lot of energy per kilogram but takes up too much room creates tank-size problems, while a fuel that is dense but energy-poor means carrying dead weight.

This is why alternatives to jet fuel face an uphill battle. Liquid hydrogen, for example, holds about two and a half times more energy per kilogram than kerosene but requires roughly four times the volume because it must be stored at extremely low temperatures in heavily insulated tanks. Research comparing alternative energy vectors for long-range aircraft found that the energy consumption per unit of cargo carried was about 11% higher for liquid hydrogen relative to Jet A, while 100% synthetic paraffinic kerosene performed essentially on par with conventional fuel.⁷ That narrow gap for SPK and wide gap for hydrogen illustrates why “drop-in” SAF fuels are seen as more practical than entirely new fuel systems for long-haul aviation in the near term.

Fuels Built for Extreme Speed

Most of the fuels discussed so far serve subsonic aircraft. Supersonic and high-speed military platforms push fuel requirements into different territory. JP-7 was developed specifically for the SR-71 Blackbird, a reconnaissance aircraft that cruised above Mach 3. At those speeds, aerodynamic heating raises skin temperatures on the aircraft to several hundred degrees. JP-7 is a highly refined kerosene with unusually low volatility, very low sulfur, and minimal aromatic content. Its thermal stability limit sits around 287 °C (560 K), meaning it can absorb significant heat in the aircraft’s fuel-cooled systems before beginning to break down.⁸

JP-7 was so stable and so resistant to ignition that the SR-71 required a separate chemical ignition system (triethylborane, a pyrophoric substance that ignites on contact with air) to start its engines. That same thermal stubbornness that made JP-7 safe at extreme temperatures made it tricky to light in the first place. The fuel is no longer produced in significant quantities since the SR-71 was retired, but research into its cracking behavior and autoignition characteristics continues to inform the design of next-generation hypersonic propulsion systems, where the fuel itself doubles as a coolant before being burned.

For hypersonic vehicles flying above Mach 5, researchers have investigated endothermic fuels that absorb large quantities of heat as they break down (crack) into smaller hydrocarbon fragments inside a heat exchanger. The cracked fuel is then injected into the combustor as a mixture of lighter, more reactive molecules. JP-7’s chemistry made it an early testbed for this concept, and understanding how cracked fuel mixtures autoignite at various temperatures and pressures remains an active research area.

Additives and Why Jet Fuel Is Not Just Kerosene

Straight distilled kerosene would fail as jet fuel. The difference between lamp oil and what goes into a wing tank is largely a matter of additives and tight compositional control. Anti-icing additives are among the most critical. At cruise altitude, fuel temperatures can drop to the point where dissolved water crystallizes into ice particles that clog filters and fuel lines. Diethylene glycol monomethyl ether (DiEGME) is a commonly used fuel-system icing inhibitor, though it comes with trade-offs: adding it to JP-8 has been shown to increase fuel density and viscosity appreciably, and it raises the ignition point by nearly 10 °C while slightly raising the freezing point compared to the neat fuel.² That means the additive changes the fuel’s behavior in measurable ways, and getting the dosage right matters.

Other common additive categories include antioxidants (preventing gum and sediment formation during storage), metal deactivators (neutralizing dissolved copper and other metals that catalyze oxidation), thermal stability improvers, lubricity agents (protecting fuel-system pumps and valves from wear), and static dissipaters (allowing static charge to bleed off safely during high-speed fueling). Military fuels like JP-8 and JP-5 mandate specific additive packages, while commercial Jet A-1 allows refiners and pipeline operators more flexibility to add them as conditions require.

Microbial Contamination in Fuel Tanks

Something most passengers never consider is that jet fuel can harbor living organisms. Bacteria, fungi, and even archaea have been found thriving at the interface between fuel and the small amounts of water that inevitably accumulate in storage tanks and aircraft wing tanks. A study profiling microbial contamination in aviation fuel at an airport found that the bacterial community was dominated by Proteobacteria and Actinobacteria, while fungal contamination was overwhelmingly from the Ascomycota phylum. All samples showed heavy levels of microbial contamination when measured with sensitive detection methods, and the study noted that traditional culture-based testing underestimated the true microbial load.⁹

Why does this matter? Microbial growth produces acidic byproducts that corrode aluminum fuel tanks from the inside. It forms biofilms and sludge that clog fuel filters. In severe cases, microbial contamination has been linked to fuel-gauge malfunctions because the organisms interfere with the capacitance-based sensors inside wing tanks. The industry addresses this through regular draining of water from sumps, biocide treatments, and fuel-quality monitoring, but the problem has proven stubbornly persistent. Warmer climates and longer fuel storage times make contamination worse, which is one reason fuel turnover rates at airports are closely managed.

Misfueling and Why Fuel Names Matter on the Ground

The existence of multiple fuel types at airports creates a real-world hazard: misfueling. The most dangerous scenario is putting jet fuel into a piston-engine aircraft that runs on aviation gasoline (avgas). Avgas and jet fuel are fundamentally different products. Avgas is a high-octane gasoline formulated for spark-ignition reciprocal engines. Jet fuel is a kerosene that works in turbine engines relying on continuous combustion. Pour kerosene into a piston engine and it will run poorly or not at all, with a risk of power loss during flight. Safety records have documented a number of accidents involving aircraft fueled with the wrong product.¹⁰

The reverse scenario, putting avgas in a turbine engine, is less immediately catastrophic but still problematic. Avgas contains tetraethyl lead, and burning leaded fuel in a turbine engine over time causes lead deposits on turbine blades and in hot-section components. To reduce misfueling risk, the industry uses color-coded fuel trucks, differently sized nozzle fittings (the overwing nozzle for avgas is smaller than the single-point pressure fitting for jet fuel), and procedural checklists. Despite these safeguards, human error still leads to occasional incidents, particularly at smaller airports where the same fueling crew handles multiple fuel types and traffic is less regimented than at major hubs.

Color coding also applies to the fuels themselves. Jet A and Jet A-1 are straw-colored to clear. Avgas 100LL is dyed blue. These visual cues help ground crews and pilots catch errors during preflight checks, though relying on color alone is never considered sufficient since contamination and aging can alter fuel appearance.

How Jet Fuel Relates to Fuels You Already Know

If you have ever used a kerosene heater or a diesel-powered vehicle, you have been around hydrocarbons close to jet fuel’s range. Diesel fuel and Jet A overlap in their distillation cuts from crude oil, and in an emergency, some turbine engines can run on diesel. The practice is not routine because diesel has different additive packages, higher sulfur content, and does not meet aviation freezing-point specifications, but it has been done in wartime and remote operations. Going the other direction, jet fuel has sometimes been blended into diesel supply chains during regional shortages, since the two products are close enough chemically that diesel engines tolerate it, though the economics rarely make sense.

Gasoline sits in an entirely different distillation range, lighter and far more volatile. The carbon chains in gasoline run from about four to twelve carbons, while jet fuel’s nine-to-sixteen-carbon range makes it heavier and less prone to evaporation. That is why gasoline is appropriate for spark-ignition engines (where you want rapid vaporization and controlled detonation) while kerosene works for turbines (where you want a steady, continuous flame in a combustion chamber). Confusing the two in an aircraft context is where misfueling incidents become dangerous.

Heating oil, meanwhile, is essentially the same distillation fraction as diesel and jet fuel but with minimal quality control. It can contain sulfur levels that would be illegal in road diesel and would corrode aviation fuel systems. The shared lineage explains why all these fuels smell somewhat alike and why cross-contamination in shared pipeline systems is a constant concern that the industry spends considerable resources monitoring.