Sustainable Aviation Fuel (SAF) Guide

What Is SAF?

Sustainable aviation fuel (SAF) is a drop-in replacement for conventional jet fuel that can be blended with kerosene up to 50% in today's aircraft with no engine modifications. Unlike fossil jet fuel, SAF is produced from renewable or waste feedstocks and delivers lifecycle CO2 reductions of 60–80% compared to the kerosene it replaces — depending on the feedstock and production pathway.

The "drop-in" characteristic is critical: SAF is certified to ASTM D7566 and once blended with conventional fuel, meets the same ASTM D1655 specification as regular Jet-A or Jet-A1. Aircraft, engines, and fuel infrastructure require no modification to use SAF blends up to 50%.

Feedstocks

SAF can be produced from a wide range of organic materials. The choice of feedstock determines the lifecycle emissions and scalability:

• Used cooking oil (UCO) and animal fats: The cheapest and most readily available feedstock today; used by most commercial SAF production; limited supply ceiling globally
• Agricultural residues: Corn stover, wheat straw, sugarcane bagasse; large potential but collection logistics are challenging
• Municipal solid waste (MSW): Non-recyclable waste converted via gasification; large feedstock base but complex permitting
• Woody biomass: Forestry residues; Neste and Shell are scaling this pathway
• Power-to-liquid (PtL) / e-fuels: Green hydrogen + captured CO2; near-zero lifecycle emissions; currently very expensive (~$10/litre) but falls with renewable electricity costs
• Algae: High theoretical yield per hectare; not yet commercially viable at scale

Production Process

The dominant commercial pathways certified by ASTM are:

• HEFA (Hydroprocessed Esters and Fatty Acids): Oils and fats hydroprocessed into hydrocarbons; accounts for ~90% of today's SAF production; mature technology
• Fischer-Tropsch (FT) synthesis: Syngas from gasified biomass or waste converted to hydrocarbons; produces SAF with exceptionally low aromatic content (reduced soot, contrail benefit)
• ATJ (Alcohol-to-Jet): Ethanol or isobutanol dehydrated and oligomerised; Lanzajet and LanzaTech are commercial leaders
• DSHC (Direct Sugar to Hydrocarbons): Sugars fermented to farnesene (Total Corbion Luminus pathway)

Current Usage

Global SAF production in 2024 was approximately 1.5–2 million tonnes — less than 0.5% of the ~300 million tonnes of jet fuel consumed annually. The bottleneck is not demand (airlines would buy more SAF if available) but production capacity. Most SAF today is produced by Neste (Finland), World Energy (USA), and LanzaJet (USA), with a production expansion wave expected in 2025–2027.

Airline Commitments

Major airlines have made SAF purchase commitments, though actual uplift lags pledges:

• United Airlines: Largest SAF buyer globally; committed to 1.5 billion gallons by 2035
• Delta Air Lines: 10-year, 7 billion gallon agreement with Gevo
• British Airways / IAG: Committed to 10% SAF by 2030; direct investments in Velocys and LanzaJet
• Lufthansa Group: SAF levy offered to passengers at booking (Compensaid)

The Cost Challenge

SAF costs roughly 3–8× the price of conventional jet fuel depending on the pathway. At $0.50–0.60/litre for conventional Jet-A1, SAF HEFA runs $1.50–3.00/litre and e-fuel pathways reach $8–12/litre. Government mandates — the EU's ReFuelEU Aviation requiring 2% SAF by 2025, rising to 70% by 2050 — and production tax credits (US Inflation Reduction Act) are the primary levers bridging the cost gap while scale is achieved.