The Growing Pressure on Aviation to Decarbonize

Commercial aviation accounts for roughly 2.5% of global carbon dioxide emissions today, and that share is projected to rise as air travel demand continues to grow in developing economies. Unlike road transport, where battery-electric vehicles are already displacing internal-combustion engines, aircraft have no near-term drop-in electric or hydrogen alternative for long-haul routes. This reality places sustainable aviation fuels (SAFs) at the center of the industry’s decarbonization strategy. The International Air Transport Association (IATA) has set a target of net-zero carbon emissions by 2050, with SAFs expected to deliver about 65% of the required emission reductions. Understanding how SAFs work, what they cost, and what stands between them and widespread deployment is essential for anyone tracking the future of commercial flight.

What Are Sustainable Aviation Fuels?

Sustainable aviation fuels are drop-in liquid fuels produced from renewable or waste-derived feedstocks rather than from crude oil. They are chemically very similar to conventional Jet A/A-1 fuel, which means they can be blended with fossil kerosene and used in existing aircraft engines and airport fueling infrastructure without modification.

Types of SAF Production Pathways

The industry has approved several technology pathways, each using different feedstocks and conversion processes:

  • HEFA (Hydroprocessed Esters and Fatty Acids): Derived from used cooking oil, animal fats, and oilseed crops. HEFA is currently the most mature and commercially available pathway, representing the vast majority of SAF volumes produced today.
  • ATJ (Alcohol-to-Jet): Converts ethanol or isobutanol from corn, sugarcane, or cellulosic feedstocks into jet fuel. ATJ offers flexibility because ethanol supply chains are already well established.
  • FT-SPK (Fischer-Tropsch Synthetic Paraffinic Kerosene): Uses gasification of municipal solid waste, agricultural residues, forestry waste, or even biomass to produce syngas, which is then converted into liquid fuel. This pathway can handle difficult feedstocks that do not compete with food production.
  • Power-to-Liquid (PtL) or e-Fuels: Combines green hydrogen (from electrolysis using renewable electricity) with captured CO₂ to synthesize liquid fuel. PtL has the highest decarbonization potential—approaching 100% lifecycle reduction—but remains extremely expensive and energy-intensive.

Approved Blend Limits

Current ASTM standards allow up to 50% blending of most SAF types with conventional Jet A/A-1 for commercial flights. Research is ongoing to certify 100% synthetic fuels, and some manufacturers have already flown demonstration flights with unblended SAF.

Carbon Reduction Potential: Lifecycle vs. Tailpipe

A common misconception is that SAF emits less CO₂ from the engine exhaust. In fact, when burned, SAF releases about the same amount of CO₂ per unit of energy as fossil jet fuel (roughly 3.16 kg CO₂ per kg of fuel). The critical difference lies in the lifecycle emissions. SAF feedstocks absorb CO₂ from the atmosphere as they grow (for biomass-based pathways) or use captured CO₂ (for PtL). That biogenic or captured carbon was already above ground, so it does not add new fossil carbon to the atmosphere.

Lifecycle analysis (LCA) must account for feedstock cultivation, harvesting, transportation, processing, and distribution. Depending on the pathway and feedstock, SAF can reduce lifecycle greenhouse gas emissions by 50% to 90% compared to conventional jet fuel. For example, used cooking oil HEFA typically achieves around 70-80% reduction, while FT-SPK from forestry residues can reach 85-90% if the process uses low-carbon energy.

Benefits Beyond Carbon

Air Quality and Contrails

SAF contains virtually no aromatic compounds and very low sulfur content compared to fossil jet fuel. This results in reduced soot and particulate matter emissions during combustion. Fewer particles mean fewer contrail ice crystals, which could reduce the warming effect of aviation contrails—currently estimated to be as large as aviation’s CO₂ impact. Early research suggests that higher SAF blend levels significantly reduce contrail ice number concentrations, offering a potential non-CO₂ climate benefit.

Energy Security and Feedstock Diversity

Countries that lack domestic oil reserves can produce SAF from locally available waste streams or agricultural residues, reducing dependence on imported petroleum. This also insulates airlines from crude oil price volatility. The diversity of approved pathways means regions can tailor their SAF production to their specific waste and resource profiles—from palm oil mill effluent in Southeast Asia to corn stover in the U.S. Midwest.

Economic Development

Building SAF refineries creates skilled manufacturing and engineering jobs in areas that may not have traditional oil refining infrastructure. The SAF industry also supports farmers and waste collectors by creating a market for agricultural residues and used cooking oil. According to the U.S. Department of Energy, scaling SAF to meet 50% of U.S. jet fuel demand could support over 300,000 jobs.

Key Challenges to Widespread Adoption

Production Cost and Price Gap

The most significant barrier is cost. SAF currently costs two to four times as much as conventional Jet A-1, which at the time of writing is around $2.50-$3.00 per gallon. HEFA tends to be the cheapest at roughly $4-$6 per gallon, while PtL can exceed $10 per gallon. Airlines operate on razor-thin margins and cannot absorb this premium without ticket price increases or regulatory mandates.

Feedstock Availability and Scalability

While there is no shortage of potential feedstocks, the logistics of collecting, transporting, and processing them are daunting. Used cooking oil, for example, is already in high demand for renewable diesel production, and supply is limited. Dedicated energy crops (like camelina or carinata) require land and water resources that could compete with food production. Municipal solid waste has low energy density and requires sorting and preprocessing. Scaling total SAF production to meet even 10% of global jet fuel demand—roughly 10 billion gallons per year—would require a massive build-out of collection and refining infrastructure.

Infrastructure and Distribution

SAF must be transported separately from fossil fuel, blended at specialized facilities, and certified before delivery to airports. Many airports lack blending equipment, storage tanks, and hydrant systems that can handle multiple fuel types. Upgrading these facilities requires capital investment from airports, airlines, and fuel suppliers, often with uncertain return on investment until SAF volumes are guaranteed.

Certification and Policy Fragmentation

Sustainability certification schemes vary by region. The EU’s Renewable Energy Directive (RED II) has different sustainability criteria than the U.S. EPA’s Renewable Fuel Standard or ICAO’s CORSIA framework. Producers must navigate multiple regulatory regimes to sell globally, increasing administrative costs and uncertainty. Airlines cannot count SAF toward their CORSIA obligations unless it meets all sustainability criteria and is backed by a certificate that tracks the fuel from cradle to grave.

Policy and Industry Momentum

Government Mandates and Incentives

Several jurisdictions have introduced mandates, blending requirements, or tax credits to close the price gap:

  • The EU ReFuelEU Aviation regulation mandates that fuel suppliers blend increasing percentages of SAF into jet fuel at EU airports, starting at 2% in 2025 and rising to 70% by 2050. Sub-targets for synthetic fuels (e-fuels) are included.
  • The U.S. Inflation Reduction Act (IRA) includes a blender’s tax credit of up to $1.75 per gallon for SAF that achieves at least 50% lifecycle emissions reduction, with additional incentives for higher reductions.
  • The UK has announced a SAF mandate requiring at least 10% SAF by 2030, with an accompanying revenue certainty mechanism.
  • Japan, Singapore, and Indonesia have all announced SAF roadmaps or targets, signaling strong Asian interest.

Industry Alliances and Offtake Agreements

Airlines are signing multi-year offtake agreements with producers to secure supply and help producers obtain financing. For example, United Airlines has invested in SAF producer NextLST and committed to purchasing billions of gallons over the next decade. The World Economic Forum’s Clean Skies for Tomorrow coalition brings together airlines, fuel producers, and airports to scale SAF. Corporate travel buyers, including Microsoft and Amazon, are also purchasing SAF credits to decarbonize their business travel.

Emerging Innovations

Alcohol-to-Jet Using Cellulosic Ethanol

LanzaJet, a major ATJ producer, opened the world’s first commercial ATJ plant in Georgia in 2024, using low-carbon ethanol from lignocellulosic feedstocks (corn stover, wood chips). This pathway avoids the food-vs-fuel debate because it uses non-edible plant material. The plant is expected to produce 10 million gallons of SAF per year, with plans to scale rapidly.

Power-to-Liquid and Direct Air Capture

Several startups are piloting PtL processes that combine green hydrogen with CO₂ captured from industrial sources or direct air capture. Companies like Twelve and HIF Global are working on modular PtL plants. The major drawback is the high cost of green hydrogen, which requires abundant renewable electricity. Analysts project PtL costs could fall to $3-$5 per gallon by 2040 as electrolyzer costs decline and renewable energy becomes cheaper.

Microalgae and Synthetic Biology

Companies such as Viridos (supported by ExxonMobil) are engineering microalgae strains that produce oil at much higher yields than traditional oilseed crops. Algae can be grown in saltwater ponds on non-arable land, avoiding competition with agriculture. If yields improve sufficiently, algae-based SAF could become cost-competitive within a decade.

Carbon Capture During Production

Some SAF production processes (especially gasification-FT) generate a concentrated CO₂ stream as a byproduct. Capturing and permanently storing that CO₂ (CCS) can turn a SAF plant into a carbon-negative facility. This is a promising avenue for future facilities but adds capital cost and requires access to geological storage sites.

The Road Ahead: Scaling From 0.1% to 65%

Today, SAF accounts for roughly 0.1-0.2% of global jet fuel consumption. To reach IATA’s 2050 target, production must grow by a factor of 500-1000 in 25 years. While that sounds improbable, precedent exists: global ethanol production grew from near zero in the 1980s to over 100 billion liters today. Policy mandates, carbon pricing, and consumer pressure are the three forces that will drive this growth.

Key milestones to watch over the next decade include: (1) the EU SAF mandate taking full effect in 2025, (2) the commercial coming of several large-scale FT and ATJ plants, (3) further cost reductions in green hydrogen for PtL pathways, and (4) the impact of the IRA blender’s credit on U.S. production capacity. If these elements align, analysts forecast SAF could reach 10-15% of global jet fuel supply by 2035, at a cost premium of 20-50% above conventional fuel.

No single solution will decarbonize aviation. Battery-electric aircraft will serve short regional routes, hydrogen may eventually power long-haul flights, and efficiency improvements (new aircraft designs, optimized flight paths) will continue to reduce fuel burn. But for the vast majority of commercial flights over the next 20-30 years, SAF is the most scalable and practical lever available. The next five years of investment, policy design, and technology maturation will determine whether sustainable aviation fuels fulfill their promise or remain a marginal niche.

For further reading: IATA SAF policy overview and industry targets, U.S. Department of Energy SAF resources, ICAO SAF and CORSIA framework, and the Boeing SAF commitment and roadmap.