How SAF Is Made: The Main Production Routes Compared

No single technology dominates Sustainable Aviation Fuel production. Instead, several distinct chemical pathways — each certified against ASTM International's D7566 aviation fuel specification — convert different waste and biomass feedstocks into a fuel that performs identically to fossil jet kerosene. Understanding how these routes differ, and what limits each one, explains why the industry is pursuing several technologies in parallel rather than settling on one winner.

HEFA: The Market Leader, With a Feedstock Ceiling

Hydroprocessed Esters and Fatty Acids, or HEFA, is currently the most commercially mature SAF production route and accounts for the large majority of SAF produced globally today. The process takes fats, oils and greases — principally used cooking oil, but also animal fats and some vegetable oils — and processes them through hydrotreatment, removing oxygen and restructuring the molecules into hydrocarbons that match the chemical profile of jet fuel.

HEFA's advantage is that it uses well-understood refining chemistry, similar to processes already used to make renewable diesel, so plants can be built relatively quickly using established engineering. Its central constraint is feedstock availability: the global supply of used cooking oil and waste fats is finite and already subject to competition from the renewable diesel industry, which uses the same feedstocks. As SAF mandates around the world scale up demand, HEFA capacity is expected to run into feedstock ceilings well before it can supply the volumes ultimately required, which is why the other routes below matter for the industry's longer-term trajectory.

Alcohol-to-Jet: Leveraging Existing Ethanol Supply Chains

Alcohol-to-Jet (AtJ) technology converts ethanol or other alcohols into jet fuel through a sequence of dehydration, oligomerisation and hydrotreatment steps. The ethanol feedstock can come from sugar or starch crops, from cellulosic biomass such as agricultural residues, or increasingly from ethanol produced via gas fermentation of waste industrial gases.

AtJ's principal advantage is that it can draw on existing global ethanol production infrastructure, particularly in markets such as the United States and Brazil with large established bioethanol industries. This gives it a faster potential scale-up path in those regions than technologies requiring entirely new production chemistry. Its constraint is the sustainability profile of the underlying feedstock: ethanol derived from food crops raises land-use and food-security questions that regulators increasingly scrutinise, pushing the industry towards cellulosic and waste-derived ethanol feedstocks that are less mature at scale.

Fischer-Tropsch: Flexible Feedstock, Higher Complexity

Fischer-Tropsch (FT) synthesis is a longer-established industrial chemistry, originally developed to convert coal into liquid fuels, that is now being applied to renewable and waste feedstocks. The process first converts a solid or gaseous feedstock into syngas — a mixture of carbon monoxide and hydrogen — through gasification, then catalytically builds that syngas into long-chain hydrocarbons suitable for refining into jet fuel.

FT's key advantage is feedstock flexibility. Because the process starts from syngas rather than from a specific molecule like ethanol or fatty acid, it can accept a wide range of inputs: municipal solid waste, forestry residues, agricultural waste, and — critically — waste gases such as landfill methane and biogas from anaerobic digestion of organic waste. This broadens the available feedstock base considerably beyond what HEFA or AtJ can draw on, and taps into waste streams that are geographically dispersed rather than concentrated. The trade-off is complexity: FT plants require gasification infrastructure and precise syngas conditioning before the Fischer-Tropsch reaction itself, making them more capital-intensive and technically demanding to build and operate than HEFA facilities.

Gas-to-Liquid and Biogas-Derived Syngas

A related and increasingly important category converts gaseous feedstocks — landfill gas, biogas from anaerobic digestion of agricultural or municipal organic waste, and in some cases captured industrial off-gases — into syngas as an intermediate step, which is then processed via Fischer-Tropsch or related synthesis into liquid fuel. This gas-to-liquid pathway is attractive because it can incorporate carbon that would otherwise be vented or flared, rather than sourcing new biomass, and because organic waste and landfill sites generating methane are widespread rather than concentrated in specific agricultural regions.

The constraint here is less about feedstock scarcity and more about plant economics and scale: converting dispersed, relatively small-volume gas streams into aviation-grade fuel requires production facilities sized and located to match available gas supply, and the syngas conditioning and conversion steps remain less commercially proven at scale than HEFA.

Why the Industry Needs All of Them

None of these routes alone can supply the volumes SAF mandates will require by 2030 and beyond. HEFA is constrained by waste oil availability, AtJ by sustainable ethanol supply, and FT and gas-based routes by capital intensity and technology maturity. Meeting rising blending mandates will depend on all of these pathways scaling in parallel, each drawing on the feedstocks it can access most efficiently, rather than any single technology emerging as a clear winner.