Sustainable
aviation fuel.
A different route to jet fuel. Explore how SAF is made, where its lifecycle emissions savings come from, and why flying still has a climate impact.
Both release CO₂ in flight. The difference must be assessed across the whole lifecycle. [6]
What is SAF?
Sustainable aviation fuel (SAF) is an alternative to fossil jet fuel that delivers lifecycle greenhouse-gas savings and meets applicable sustainability criteria. It can be made from waste oils, biomass, or captured CO₂ and hydrogen. Alternative feedstocks alone do not make a fuel sustainable; its sourcing, production and certification matter. [1] [2]
Designed for existing aircraft
Approved SAF components are blended and certified to meet jet-fuel specifications. A compliant drop-in blend can use existing aircraft engines and fuel infrastructure. Raw cooking oil cannot go into a jet’s tanks. [1]
Still a combustion fuel
Burning SAF still releases CO₂ at a level broadly comparable to fossil jet fuel per unit of energy. Its potential benefit comes from the carbon source and the full production-and-use cycle. Lower lifecycle emissions do not mean zero exhaust emissions. [6]
More than one route to jet fuel
Oils and fats
Used cooking oils, animal fats and other suitable oils are processed with hydrogen into hydrocarbons. HEFA means hydroprocessed esters and fatty acids. [4]
Alcohol into kerosene
Alcohols such as ethanol become jet-fuel molecules through a series of chemical reactions. Where the alcohol comes from matters to the final footprint. [1]
Biomass and residues
Biomass can be gasified into synthesis gas (mainly hydrogen and carbon monoxide), then converted into liquid hydrocarbons. A technically approved process does not make every feedstock sustainable: fossil inputs can also use Fischer–Tropsch chemistry. [4]
Electricity into e-fuel
Electricity splits water to produce hydrogen, which is combined with captured CO₂ and converted into synthetic fuel. The electricity supply and carbon source strongly affect the footprint; the process is energy-intensive. [2]
- SourceCollect eligible feedstocks.
- ConvertProduce jet-fuel molecules.
- Blend & certifyMeet fuel specifications.
- FlyDeliver through the fuel network.
Fuel quality approval and sustainability certification answer different questions: can it be used safely, and does its production meet environmental criteria? Both matter. [4]
Count the entire journey
A lifecycle assessment includes feedstock production or collection, processing, transport, fuel conversion, distribution and combustion. Land-use change can erode or even outweigh the expected savings from biofuels. The same fuel pathway can have different footprints depending on its energy supply and feedstock. [3] [6]
A claim needs a defined fuel pathway, lifecycle method and fossil-fuel baseline. A saving for the SAF component also differs from the saving for the complete blend.
| Compare | Fossil jet fuel | Certified SAF blend |
|---|---|---|
| Carbon source | Petroleum extracted from the ground. | Alternative feedstocks, plus any fossil fuel in the blend. |
| CO₂ in flight | Released during combustion. | Still released. SAF is a combustion fuel. |
| Lifecycle footprint | The fossil baseline used for comparison. | Depends on the pathway, energy inputs, land use and SAF share. |
| Aircraft & fuel system | Conventional jet-fuel infrastructure. | A compliant drop-in blend can use the existing fleet and infrastructure. |
Compare fuels on the same energy basis and within the same lifecycle boundary. Fuel compatibility and climate performance are separate checks. [1] [3] [6]
Build a blend. See the difference.
Change the SAF share and its assumed lifecycle saving. Compare fuel supplying the same amount of energy with an all-fossil baseline.
Teaching model · Energy shares, not approved mixing limits
Each preset assumes an 80% saving for the SAF component. That is an illustrative assumption, not a guarantee or industry average. The 100% example is a mathematical scenario, not an operational approval.
50% SAF energy share × 80% lifecycle saving = 40% blend saving.
- Fossil fuel emissions50%
- SAF lifecycle emissions10%
- Avoided emissions40%
60% of the fossil-fuel baseline remains. Hatched area shows the 40% avoided.
How SAF share changes the saving
Follow your assumption across the full energy-share range. The dot marks your current blend.
Blend lifecycle saving (%)
SAF share of fuel energy (%)
What this model includes
Assumes equal total fuel energy and a common lifecycle baseline. Estimates lifecycle fuel greenhouse-gas savings, not the reduction in a flight’s total climate impact. Excludes non-CO₂ climate effects and aircraft manufacturing.
The sliders explore values from 0–100%. This simplified model does not cover pathways with negative lifecycle emissions or emissions above the fossil baseline. Certification blend limits are typically expressed by volume, so these energy shares are not a fuel-mixing recipe.
Better fuel is only part of the answer
Supply and cost
Scaling production requires suitable feedstocks, new facilities and investment. Synthetic fuels also depend on affordable low-carbon energy. SAF generally costs more than fossil jet fuel. [5]
Climate effects beyond CO₂
SAF does not eliminate water vapour, nitrogen oxides or all contrails. Lower-soot fuel can reduce contrail ice formation under some conditions, but that is not a guarantee of contrail-free flight. [6]
Can an airliner fly on 100% SAF?
Demonstration flights and research do not mean every aircraft and fuel combination is cleared for routine use. Approved limits depend on the fuel pathway and applicable specifications. ICAO’s overview, which cites July 2023 approval data, lists a 50% maximum for HEFA-SPK and several other pathways. It is not a live specification. The current fuel standard and aircraft approvals govern operational use. [4] [2]
Is all SAF made from plants?
No. Biomass routes are one family; synthetic e-fuels can use captured carbon and hydrogen. The energy and material inputs determine whether a route delivers meaningful lifecycle savings. [2]
Does “sustainable” mean no environmental trade-offs?
No. Land use, biodiversity, water, supply-chain traceability and competing uses of feedstocks matter alongside greenhouse gases. CORSIA eligibility requires compliance with sustainability criteria and certification by an approved scheme. [7]
Sources & further reading
AI-assisted explainer · Fact-checked 11 October 2026 against the linked primary sources. Fuel standards and approvals evolve; consult the current specification for operational use.
- U.S. DOE — Sustainable Aviation Fuel: production and distribution
- EASA — What are sustainable aviation fuels?
- ICAO — SAF lifecycle assessment
- ICAO — SAF conversion processes and blending limits
- EASA — SAF market and production costs
- EASA — How sustainable are SAF?
- ICAO — CORSIA eligible fuels and sustainability certification
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