Sustainable Aviation Fuel: Potential and Limitations

Quick verdict

Sustainable aviation fuel (SAF) is a promising but partial solution to aviation’s carbon emissions. It can reduce lifecycle greenhouse gas emissions by up to 80% compared to conventional jet fuel, and it is compatible with existing aircraft and infrastructure. However, current production is less than 1% of total jet fuel demand, costs are 2–5 times higher, and scaling is limited by feedstock availability and sustainability concerns. SAF is a necessary transitional tool, especially for long-haul flights where electrification and hydrogen are not yet viable, but it cannot fully decarbonize aviation alone.

Problem addressed

Aviation accounts for approximately 2–3% of global CO₂ emissions, and its share is projected to grow as other sectors decarbonize. Aircraft emissions also include non-CO₂ effects (e.g., contrails, nitrogen oxides) that may double the climate impact. Unlike road transport, aviation cannot easily switch to batteries or hydrogen for long-haul flights due to energy density requirements. SAF aims to reduce the net carbon footprint of flying by replacing fossil kerosene with fuels derived from renewable or waste-based sources, thereby addressing the sector’s hard-to-abate emissions.

How the solution works

Sustainable aviation fuels are drop-in liquid hydrocarbons that can be blended with conventional jet fuel (up to 50% for most certified pathways) and used in existing aircraft and fueling infrastructure. They are produced from a variety of feedstocks and conversion processes:

• Hydroprocessed esters and fatty acids (HEFA): From waste oils, fats, and oil crops.
• Alcohol-to-jet (ATJ): From ethanol or isobutanol derived from biomass or waste.
• Fischer–Tropsch (FT): From gasified biomass or municipal solid waste.
• Power-to-liquid (PtL) / e-fuels: From captured CO₂ and green hydrogen.

These fuels are chemically similar to fossil kerosene but can offer significant lifecycle emission reductions because the carbon released during combustion was recently captured from the atmosphere (via biomass growth or direct air capture), creating a short carbon cycle.

Evidence strength

The evidence base for SAF is moderate. Lifecycle analyses published in peer-reviewed journals consistently show emission reductions of 50–80% for HEFA and advanced pathways compared to fossil jet fuel, depending on feedstock and production methods. Over 450,000 commercial flights have used SAF blends since 2011, demonstrating technical compatibility. However, real-world production data is limited: global SAF output in 2022 was around 300–450 million liters, less than 0.5% of total jet fuel demand. Long-term sustainability studies are sparse, and indirect land-use change (ILUC) effects remain uncertain and contested. Most projections of future SAF volumes rely on techno-economic models with significant assumptions.

Potential scale

Theoretical potential is large: the aviation industry targets 10% SAF use by 2030 and 65% by 2050 (IATA). However, practical scalability is constrained by feedstock availability. Waste-based feedstocks (used cooking oil, tallow) are limited; estimates suggest they could meet 2–5% of global jet fuel demand. Advanced feedstocks (agricultural residues, energy crops, municipal waste) could increase this to 10–30%, but compete with other sectors (e.g., road transport, chemicals) and face logistical hurdles. Power-to-liquid fuels offer virtually unlimited potential if renewable electricity and CO₂ capture become abundant and cheap, but that scenario is decades away. Realistically, SAF could cover 5–20% of aviation fuel by 2050 under aggressive policy and investment.

Cost considerations

SAF currently costs 2–5 times more than conventional jet fuel, with HEFA at $1.5–$3 per liter versus $0.5–$0.7 for Jet A-1. Advanced pathways (ATJ, FT) are even more expensive, and PtL is estimated at $3–$6 per liter. Costs are expected to decline with scale and technology learning, but parity with fossil kerosene is unlikely without strong policy support (e.g., carbon pricing, mandates, subsidies). The price premium adds significant operating costs for airlines, which operate on thin margins, and would likely be passed on to passengers or require government intervention.

Implementation time

SAF can be deployed immediately in existing aircraft and infrastructure, with blending mandates already in place in some jurisdictions (e.g., EU, UK). However, scaling production to meaningful levels will take decades. Building new biorefineries and PtL plants requires 3–7 years per facility, and feedstock supply chains need development. The aviation industry’s 2030 target of 10% SAF use is ambitious given current production capacity and growth rates. Full decarbonization via SAF alone would require massive investments and technological breakthroughs, likely extending well beyond 2050.

Environmental benefits

Lifecycle analyses indicate SAF can reduce CO₂ emissions by 50–80% compared to fossil jet fuel, with some pathways achieving up to 90% reduction. Particulate matter and sulfur emissions are also lower, which may reduce contrail formation. However, actual benefits depend heavily on feedstock choice and production methods. For example, HEFA from waste oils has high reduction potential, while some crop-based pathways may offer minimal benefits if land-use change emissions are included. SAF does not eliminate CO₂ emissions at the point of combustion, and non-CO₂ climate effects (e.g., contrails, NOx) persist, though some studies suggest aromatic-free SAF could reduce contrail formation.

Social and economic co-benefits

SAF production can create jobs in agriculture, waste management, and advanced manufacturing. It can improve energy security by diversifying fuel sources and reducing dependence on crude oil imports. Using waste oils and residues as feedstocks can reduce waste disposal problems. In developing regions, sustainable feedstock cultivation could provide rural income, though careful governance is needed to avoid negative social impacts. PtL pathways could stimulate growth in renewable energy and hydrogen sectors.

Risks and unintended consequences

Large-scale SAF deployment carries significant risks. Crop-based feedstocks may compete with food production, driving up food prices and causing indirect land-use change that releases carbon from forests and peatlands. Even waste-based feedstocks have limits; for example, used cooking oil collection is already near maximum in many regions, and fraudulent labeling of virgin palm oil as waste has been documented. Power-to-liquid fuels require enormous amounts of renewable electricity and captured CO₂, potentially diverting clean energy from other sectors. There is also a risk that SAF could be used to justify continued growth in aviation, undermining demand-side measures and modal shift. Finally, the high cost may lead to unequal access, with only wealthy travelers and routes benefiting.

Where it works best

SAF is most viable in regions with abundant sustainable feedstocks (e.g., agricultural residues in the US Midwest, forestry waste in Scandinavia, municipal solid waste in urban centers) and strong policy support (e.g., EU’s ReFuelEU mandate, US SAF Grand Challenge). It is particularly suited for long-haul flights where electrification and hydrogen are not feasible in the near term. Airlines with modern fleets and hub-and-spoke models can integrate SAF more easily. Countries with existing biofuel industries and renewable energy capacity can leverage infrastructure and expertise.

Where it may not work

SAF is less suitable for short-haul flights, where electrification or hydrogen may become competitive sooner. Regions with limited feedstock availability, weak governance, or high land-use pressures may struggle to produce SAF sustainably. In areas where renewable electricity is scarce, PtL pathways would be prohibitively expensive and could compete with more urgent electrification needs. SAF is not a viable standalone solution for aviation’s non-CO₂ climate effects, which require additional mitigation strategies. Over-reliance on SAF without demand-side measures (e.g., frequent flyer levies, modal shift to rail) could lock in high emissions.

Comparison with alternatives

Alternatives to SAF for reducing aviation emissions include:

• Operational efficiency: Improved air traffic management, fleet renewal, and operational procedures can reduce fuel burn by 10–20% at low or negative cost, but gains are incremental.
• Hydrogen aircraft: Zero-emission at point of use, but requires new aircraft designs, infrastructure, and green hydrogen production; likely limited to short/medium-haul before 2050.
• Battery-electric aircraft: Zero-emission, but energy density limits range to <500 km for small aircraft; not viable for long-haul in foreseeable future.
• Modal shift: Replacing short-haul flights with high-speed rail can eliminate emissions, but requires infrastructure investment and is limited to certain corridors.
• Carbon offsets: Cheaper than SAF but face credibility issues and do not reduce aviation’s own emissions.

SAF is the only drop-in option that can address long-haul emissions in the near to medium term, making it complementary to these alternatives rather than a substitute.

Case studies

United Airlines (USA): United has committed to purchasing 1.5 billion gallons of SAF over 20 years and invested in several SAF producers. It operates regular SAF-blend flights from Los Angeles and San Francisco, but SAF still accounts for less than 0.1% of its total fuel use.

Neste (Finland): Neste is the world’s largest producer of HEFA-based SAF, with a capacity of 1.5 million tons per year by 2023. Its fuel is used by airlines including Lufthansa, KLM, and Alaska Airlines. However, its feedstock relies heavily on used cooking oil, which faces supply constraints and fraud risks.

Fulcrum BioEnergy (USA): Fulcrum aims to produce SAF from municipal solid waste via gasification and FT synthesis. Its first commercial plant in Nevada has faced delays and cost overruns, highlighting the challenges of scaling advanced pathways.

EU ReFuelEU Aviation mandate: The EU requires fuel suppliers to blend increasing shares of SAF, starting at 2% in 2025 and reaching 70% by 2050, with sub-mandates for synthetic fuels. This policy is expected to drive investment but may raise costs for European airlines.

Final assessment

Sustainable aviation fuel is a critical but incomplete solution for decarbonizing aviation. It offers the only near-term pathway to reduce emissions from long-haul flights, and its drop-in nature allows rapid deployment. However, its potential is bounded by feedstock limits, high costs, and sustainability risks. SAF should be pursued aggressively where it makes sense—using waste-based feedstocks with strong safeguards, supported by mandates and incentives—but it cannot replace the need for demand management, operational efficiency, and long-term technological shifts. Policymakers and industry must treat SAF as one element of a broader strategy, not a license for unconstrained growth.