“SAF” is an umbrella term that describes several production pathways and feedstock classes. The main currently commercialized technologies are:
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HEFA (Hydroprocessed Esters and Fatty Acids) — converts fats, oils, and greases (used cooking oil, tallow) into paraffinic kerosene. HEFA is the most widely deployed commercial option today and is used in many airline supply deals. HEFA SAF can deliver substantial lifecycle emissions reductions when feedstocks are waste-based.
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FT-SYNTHESIS / Biomass-to-Liquid (BtL) — biomass gasification followed by Fischer-Tropsch synthesis to produce hydrocarbons. This pathway can process woody residues and agricultural residues and offers potential for deeper GHG reductions depending on feedstock and lifecycle assumptions.
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Alcohol-to-Jet (ATJ) — converts ethanol, butanol or other Aviation Alternative Fuel to jet-grade hydrocarbons. ATJ can make use of cellulosic ethanol or bioethanol; it has room to scale where feedstock ethanol supplies exist.
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Power-to-Liquid / e-SAF (PtL/e-SAF) — uses renewable electricity to produce hydrogen (via electrolysis), synthesizes CO₂ with hydrogen into hydrocarbons (via Fischer-Tropsch or other synthesis routes). e-SAF is the route with the largest theoretical lifecycle GHG reductions (close to zero if powered by renewables and using biogenic or direct-air-captured CO₂), but it is capital-intensive and energy-intensive today and will take time to scale meaningfully.
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Synthetic kerosenes and co-processing — refinery co-processing of renewable feedstocks into existing refining infrastructure is also in use to produce SAF blends.
Feedstock categorization is important for sustainability outcomes: waste-based feedstocks (used cooking oil, municipal solid waste, animal fats) generally offer favorable lifecycle emissions profiles and are prioritized by many regulators; crop-based biofuels raise land-use concerns and face sustainability scrutiny; e-SAF removes many land-use issues but requires large renewable power and CO₂ sources.
Standards and certification frameworks (ASTM fuel approvals, national lifecycle accounting rules) control which fuels are eligible as SAF. These standards ensure safety and compatibility with existing aircraft and infrastructure.