How Sustainable Aviation Fuels Are Made, and Why Their Climate Impact Varies

Sustainable Aviation Fuel (SAF) is crucial for aviation's net-zero goals, but its climate impact varies significantly based on production pathways and feedstocks. Understanding lifecycle assessments is essential to verify the true emissions reductions of different SAF types.

Dr. Aris Thorne

October 7, 2026 · 4 min read

Sustainable Aviation Fuel (SAF) is a critical component in the aviation industry's strategy to achieve net-zero carbon emissions by 2050, with the International Air Transport Association (IATA) estimating it could account for up to 65% of the necessary emissions reductions. Unlike conventional jet fuel derived from fossil sources, SAF is produced from renewable biomass or by synthesizing it from renewable electricity and captured carbon. However, not all SAFs are created equal. Their potential to reduce greenhouse gas emissions varies widely depending on the raw materials, or feedstocks, used and the specific technological pathway employed in their production.

SAFs fall into two main categories: biofuels made from biomass and synthetic fuels, often called e-fuels or e-kerosene, produced from green hydrogen and carbon dioxide. While some SAFs can cut lifecycle emissions by up to 80% compared to their fossil-based counterparts, others made from certain crops may not reduce emissions at all. Understanding these production pathways is key to evaluating the true climate benefit of any given sustainable fuel.

The Importance of Lifecycle Assessment for SAF

The climate benefit of Sustainable Aviation Fuel is not measured at the aircraft's exhaust pipe—where its emissions are chemically similar to conventional fuel—but across its entire production lifecycle. This comprehensive accounting, known as a lifecycle assessment (LCA), is what determines a fuel's actual sustainability. According to the International Council on Clean Transportation (ICCT), the feedstock is the most critical factor for assessing the sustainability of biofuels.

An LCA calculates the total greenhouse gas emissions associated with producing the fuel, from cultivating and harvesting the feedstock, transporting it, and processing it, to the energy consumed during the fuel conversion process itself. The climate benefit arises because SAF utilizes waste, residues, or recycled carbon instead of extracting new fossil carbon from the ground. As the IATA explains, this non-fossil origin is what enables the reduction of fossil-derived carbon emissions. The significant variation in potential GHG reductions across different SAFs is a direct result of these lifecycle factors.

Comparative Overview of SAF Production Pathways

Several distinct technological pathways for producing SAF have been certified for use, each with its own set of feedstocks, conversion processes, and potential for reducing greenhouse gas emissions. The most mature technologies are already in commercial use, while more advanced pathways hold significant long-term promise.

A comparison of the primary production pathways for Sustainable Aviation Fuel, detailing their inputs, processes, and documented climate benefits.
Pathway Name	Common Feedstock(s)	Basic Process Description	Lifecycle GHG Reduction vs. Jet Fuel
HEFA (Hydroprocessed Esters and Fatty Acids)	Waste fats, oils, and greases (e.g., used cooking oil, animal fats, distillers corn oil), as well as plant oils.	Oil-based feedstocks are treated with hydrogen (hydroprocessed) to break down fatty acid chains, followed by hydroisomerization and hydrocracking to produce a drop-in fuel.	Up to 80% reduction when using waste-derived feedstocks, according to analysis from both the ICCT and IATA.
FT-SPK (Fischer-Tropsch Synthetic Paraffinic Kerosene)	Woody biomass, municipal solid waste, agricultural and forest residues, and dedicated energy crops.	Biomass is converted into a synthesis gas (syngas) through gasification. A Fischer-Tropsch synthesis reaction then converts the syngas into liquid fuel.	Reduction potential varies significantly based on the specific feedstock and the energy source used for the gasification process.
ATJ (Alcohol-to-Jet)	Alcohols such as ethanol and isobutanol, which can be derived from various biological or industrial sources.	Alcohols undergo a series of chemical reactions, including dehydration, oligomerization (linking smaller molecules into longer chains), and hydrogenation to create jet fuel.	The climate benefit is dependent on the lifecycle emissions of the alcohol feedstock used in the process.
PtL (Power-to-Liquid) / e-fuels	Renewable electricity, water (H₂O), and captured carbon dioxide (CO₂).	Renewable electricity powers the electrolysis of water to produce green hydrogen. This hydrogen is then combined with captured CO₂ to create syngas, which is converted to fuel via the Fischer-Tropsch method.	Can achieve reductions above 90%, with the potential for negative emissions, but this is contingent on the use of 100% renewable electricity for production.

Power-to-Liquid (PtL) / e-Fuel: A Detailed Look

The Power-to-Liquid (PtL) pathway, which produces what are known as e-fuels or e-kerosene, represents one of the most advanced and promising methods for creating SAF. Unlike biofuel pathways that rely on biomass, the PtL process synthesizes fuel directly from renewable energy and captured carbon, offering a pathway with potentially very high emissions reductions.

The production process involves several key steps:

Green Hydrogen Production: The process begins with electrolysis, where renewable electricity—from sources like wind turbines, solar photovoltaics, or geothermal energy—is used to split water (H₂O) into hydrogen (H₂) and oxygen.
Carbon Dioxide Capture: Concurrently, carbon dioxide (CO₂) is captured. This can be done through Direct Air Capture (DAC) technology, which pulls CO₂ from the atmosphere, or by capturing it from industrial point sources like power plants.
Syngas Formation: The green hydrogen and captured carbon dioxide are then reformed into synthesis gas, or syngas, a mixture of hydrogen and carbon monoxide.
Fuel Synthesis: Finally, the syngas is processed using the well-established Fischer-Tropsch method, which converts it into liquid hydrocarbons, including a synthetic kerosene that can be blended with conventional jet fuel.