SAF, or Sustainable Aviation Fuel, is an alternative to conventional jet kerosene designed to reduce aviation’s lifecycle greenhouse gas emissions. It can be produced from eligible waste materials, renewable resources and synthetic inputs. Unlike many emerging aircraft technologies, approved SAF can be blended with conventional aviation fuel and used in compatible aircraft without requiring an entirely new fleet.
This compatibility makes the fuel an important option for airlines seeking to lower emissions while maintaining existing routes. Large commercial aircraft need energy-dense fuel, particularly on long-distance journeys, where current battery technology cannot easily provide the required range and payload.
However, sustainable aviation fuel is not automatically carbon-neutral. Aircraft engines still release carbon dioxide when burning it. The potential benefit comes from reducing emissions across the fuel’s lifecycle, including raw material collection, processing, production and transport.
The source of the fuel matters considerably. Waste-derived fuels may offer meaningful savings when produced responsibly, while synthetic fuels can have lower lifecycle emissions when made with low-carbon electricity and suitable carbon sources. Poorly managed feedstocks or energy-intensive production can reduce these benefits.
In the UK, the Sustainable Aviation Fuel Mandate took effect on 1 January 2025, establishing increasing obligations for fuel suppliers. The policy signals that alternative aviation fuels will play a growing role in the industry’s transition, although the exact pace will depend on investment, supply and cost.
Understanding how SAF works, where its environmental benefits come from and what limits its expansion is essential for evaluating whether it can deliver meaningful progress towards cleaner aviation.
What Is Sustainable Aviation Fuel?
Sustainable aviation fuel is a category of alternative fuels that meet relevant technical and sustainability requirements for aviation use. It is designed to replace some or, where approved and technically appropriate, more of the fossil-derived jet fuel used by aircraft.
The International Civil Aviation Organization recognises SAF as a key pathway for reducing aviation’s carbon dioxide emissions. Its lifecycle assessment framework considers emissions from feedstock production and collection through fuel processing, distribution and combustion.
SAF can be produced through several pathways. These include processing waste fats and oils, converting suitable biomass into hydrocarbons and producing synthetic fuel from hydrogen and carbon dioxide.
The resulting fuel must meet applicable aviation fuel specifications. Approved production pathways have defined requirements, including limits on blending with conventional fuel where applicable.
The word sustainable is important. A fuel’s environmental value depends on evidence that its production meets recognised criteria. Renewable origin alone does not prove that a product delivers substantial climate benefits.
How Is SAF Produced?
Different production methods use different materials and technologies. Each has advantages, limitations and varying levels of commercial maturity.
Hydroprocessed esters and fatty acids
The HEFA process converts eligible fats, oils and greases into hydrocarbons suitable for aviation fuel. Used cooking oil and certain waste fats can serve as feedstocks.
HEFA is an established route for producing alternative aviation fuel. However, supplies of eligible oils and fats are limited, and competition from other industries can constrain future expansion.
Biomass conversion
Agricultural residues, forestry residues and certain other forms of biomass can be converted into aviation fuel through processes such as gasification and subsequent fuel synthesis.
This approach could broaden the range of available feedstocks. Its success depends on reliable residue supplies, efficient processing and the environmental effects of collecting and transporting biomass.
Alcohol-to-jet
The alcohol-to-jet pathway converts suitable alcohols into hydrocarbons that can be processed into aviation fuel. The alcohol may be produced from eligible biomass or other qualifying inputs.
Its potential depends on the availability of sustainable feedstocks, conversion efficiency and the cost of building commercial-scale facilities.
Power-to-liquid synthetic fuel
Synthetic aviation fuel can be produced using hydrogen and carbon dioxide. The hydrogen may be generated through electrolysis powered by low-carbon electricity, while the carbon comes from an eligible source.
This pathway could reduce dependence on limited waste oils. However, it requires substantial energy and suitable infrastructure for hydrogen production, carbon sourcing and fuel synthesis.
SAF Compared With Conventional Jet Fuel
| Feature | Sustainable aviation fuel | Conventional jet fuel |
| Primary inputs | Eligible renewable materials, waste or synthetic inputs | Petroleum |
| Lifecycle emissions | Potentially lower, depending on production | Generally higher |
| Aircraft use | Approved pathways and blending requirements apply | Established standard fuel |
| Production costs | Generally higher at present | Generally lower |
| Supply | Limited relative to total aviation demand | Extensive global infrastructure |
| Climate benefit | Depends on verified lifecycle performance | Adds fossil carbon to the atmosphere |
SAF does not eliminate all aviation emissions. Its main advantage is the potential to reduce lifecycle carbon emissions while retaining the energy characteristics needed for existing aircraft.
Environmental Benefits and Risks
The climate benefit of alternative aviation fuel must be assessed across its entire production chain.
The UK government’s SAF Mandate guidance requires eligible fuel to achieve at least a 40% greenhouse gas reduction against the fossil-fuel comparator. The actual reduction varies by pathway, and the figure should not be treated as a guaranteed saving for every fuel product.
Three issues deserve particular attention.
Feedstock competition: Used cooking oil and waste fats are valuable resources with existing uses. Increasing demand can encourage substitution with less sustainable materials or make it harder to verify where supplies originate.
Land-use change: Expanding agricultural production for fuel can create pressure on land, biodiversity and food systems. Any emissions released through direct or indirect land-use changes can reduce the climate benefit.
Energy consumption: Synthetic fuel production requires significant energy. If that energy comes from carbon-intensive sources, the resulting fuel may deliver much smaller savings than expected.
The International Civil Aviation Organization’s lifecycle methodology accounts for relevant production and supply-chain emissions, with additional considerations for indirect land-use change and applicable credits. Independent certification helps establish whether a fuel meets the relevant sustainability requirements.
A further limitation is that lower lifecycle carbon emissions do not mean zero environmental impact. Aircraft continue to produce nitrogen oxides, water vapour and other emissions associated with flight. SAF should therefore be understood as one part of aviation decarbonisation, rather than a complete solution to every environmental effect.
The UK SAF Mandate Explained
The UK introduced its Sustainable Aviation Fuel Mandate on 1 January 2025. It requires fuel suppliers to provide an increasing proportion of eligible SAF within the aviation fuel mix.
The policy uses tradeable certificates linked to the greenhouse gas savings delivered by qualifying fuels. It also includes provisions designed to encourage different production pathways and manage the risks of insufficient supply.
The following figures distinguish the statutory annual obligations from rounded long-term policy targets.
| Year | Main SAF obligation | Power-to-liquid obligation |
| 2025 | 2.041% | 0% |
| 2026 | 3.734% | 0% |
| 2027 | 5.485% | 0% |
| 2028 | 7.082% | 0.215% |
| 2030 | 10.556% | 0.556% |
| 2040 | 22% policy target | 3.5% policy target |
The figures for 2025–2030 reflect the percentages specified in the statutory framework. The 2040 figures are rounded policy targets, not a claim that the precise statutory schedule is identical to those rounded numbers.
The mandate also introduces limits on the share of qualifying SAF that can come from the HEFA pathway over time. From 2027, these limits are intended to encourage the development of other production technologies.
For suppliers, the framework creates demand and a financial incentive to deliver eligible fuel. For producers, it may improve the case for investing in new facilities. However, compliance costs and fuel availability will influence how quickly the industry can expand.
Why SAF Remains Expensive
The cost of producing sustainable aviation fuel is affected by raw material prices, conversion technology, plant construction, energy requirements and distribution.
Conventional jet fuel benefits from a large, established global supply chain. Alternative fuel producers must compete for eligible feedstocks while financing facilities that may be more expensive to operate.
Synthetic fuels face additional challenges because hydrogen production, carbon sourcing and fuel synthesis require significant energy and specialised equipment.
Policy support can help reduce investment risk, but it cannot guarantee low prices. Airlines and fuel suppliers must still manage the difference between the cost of alternative fuels and conventional kerosene.
That difference matters because fuel is a major airline operating expense. Higher costs may affect ticket prices, airline margins or the pace at which carriers adopt cleaner fuels.
Another issue is the gap between announced production capacity and fuel actually delivered. A proposed plant may face planning delays, financing difficulties or shortages of raw materials. Market assessments should therefore distinguish planned projects from facilities that are operating and supplying certified fuel.
The Future of SAF in 2027
In 2027, SAF development is likely to focus on expanding reliable production, diversifying feedstocks and improving access to investment.
The UK’s statutory framework increases the main obligation to 5.485% in 2027. Its HEFA cap also begins to apply, encouraging a broader mix of qualifying technologies. These requirements create incentives for investment but do not guarantee that sufficient fuel will be available at the lowest possible cost.
Power-to-liquid fuel will become subject to a separate UK obligation in 2028. That provides a policy signal for synthetic fuel development, although the technology’s energy requirements and capital costs remain substantial.
Internationally, the International Civil Aviation Organization continues to support the development of sustainable aviation fuels through policy frameworks, lifecycle methodologies and sustainability criteria. Its global framework includes an aspirational goal of reducing international aviation’s carbon dioxide emissions by 5% by 2030 through cleaner aviation energies, compared with a scenario without their use.
This is an industry-wide ambition, not a guarantee that SAF alone will achieve the reduction.
Progress in 2027 should be assessed through operating production facilities, verified fuel volumes, lifecycle savings and investment in low-carbon energy. Announcements and targets are useful indicators, but actual delivery will determine whether the sector is making measurable progress.
Key Takeaways for Airlines and Travellers
- Check lifecycle performance: The sustainability of a fuel depends on its complete production chain, not just its feedstock.
- Look beyond headline targets: Regulatory obligations must be supported by real production and delivery.
- Diversify production methods: Multiple pathways can reduce reliance on limited waste oils and fats.
- Account for energy demand: Synthetic fuels need substantial low-carbon electricity to deliver strong climate benefits.
- Consider the financial impact: Higher fuel costs can affect airlines, suppliers and potentially passengers.
- Maintain a broader climate strategy: Aircraft efficiency and operational improvements remain important alongside alternative fuels.
Frequently Asked Questions
What does SAF stand for?
SAF stands for Sustainable Aviation Fuel. It describes alternative aviation fuels made from eligible renewable materials, waste or synthetic inputs that meet applicable technical and sustainability standards.
Is sustainable aviation fuel better for the environment?
It can be. Its climate benefit depends on feedstock sourcing, processing, energy use, transport and other lifecycle factors. Verified lifecycle assessments provide a more reliable comparison than fuel origin alone.
Can commercial aircraft use SAF?
Yes. Approved SAF pathways can be used in compatible aircraft when the fuel meets applicable specifications and blending requirements. Existing aviation infrastructure can generally accommodate approved blends.
Is SAF carbon-neutral?
No. Burning SAF releases carbon dioxide. Its potential advantage is lower lifecycle emissions compared with conventional jet fuel, rather than the elimination of exhaust emissions.
Why is sustainable aviation fuel so expensive?
Production costs are influenced by limited feedstocks, specialised processing facilities, energy consumption and supply-chain constraints. Synthetic fuel can also require significant investment in electricity, hydrogen and carbon-sourcing infrastructure.
Will SAF replace conventional jet fuel by 2030?
No. Current UK policy requires a rising proportion of eligible alternative fuel rather than complete replacement. Production capacity, costs and feedstock availability will determine how quickly adoption grows.
What is the difference between bio-based SAF and synthetic SAF?
Bio-based SAF is made from eligible biological materials, including certain waste oils and residues. Synthetic SAF can be made from hydrogen and carbon dioxide using industrial processes, with its environmental performance depending heavily on the energy source.
Conclusion
Sustainable aviation fuel provides a practical route towards lower aviation lifecycle emissions because approved products can work within existing aircraft and airport systems. This makes it particularly relevant to long-distance commercial aviation, where other low-carbon technologies face significant technical challenges.
However, the environmental benefits depend on responsible sourcing, efficient manufacturing and transparent emissions accounting. Limited feedstocks, high production costs and the energy demands of synthetic fuels remain barriers to widespread adoption.
The UK’s SAF Mandate and international aviation initiatives provide important signals for future investment. Their success will depend on whether producers can deliver enough qualifying fuel while maintaining credible sustainability standards and managing costs.
By 2027, meaningful progress should be judged through verified production, actual fuel deliveries and measured lifecycle emissions savings. SAF is an important part of aviation’s climate strategy, but it must work alongside more efficient aircraft, improved operations and other developing technologies. Its long-term value will depend not on ambitious claims, but on demonstrable environmental benefits at commercial scale.
Methodology
This article was prepared using published guidance and legislation from the UK Department for Transport, the UK statutory framework for the SAF Mandate and the International Civil Aviation Organization’s material on fuel conversion pathways and lifecycle emissions.
Regulatory figures were checked against the published statutory schedule, distinguishing annual obligations from rounded long-term policy targets. Environmental claims are presented with qualifications because actual emissions savings vary by feedstock, production process and energy source.
No independent fuel testing, industry interviews or original field reporting was conducted for this article. Production costs and future availability are discussed qualitatively because they vary across technologies and projects. A human editor should verify the latest official statistics, reference details and author credentials before publication.
References
Department for Transport. (2024). The SAF Mandate: An essential guide. UK Government.
Department for Transport. (2026). Sustainable Aviation Fuel (SAF) Mandate statistics: 2026 first provisional release. UK Government.
International Civil Aviation Organization. (n.d.). Life cycle emissions of aviation fuels. ICAO.
International Civil Aviation Organization. (n.d.). SAF conversion processes. ICAO.
International Civil Aviation Organization. (n.d.). Sustainability of aviation fuels. ICAO.
United Kingdom. (2024). The Renewable Transport Fuel Obligations (Sustainable Aviation Fuel) Order 2024. UK Statutory Instrument.
