The Basics of SAF
Air travel is an essential part of modern life. We think nothing of traveling by plane for vacation or work. But how often do we think about the fuel powering our planes? Sustainable aviation fuel (SAF), sometimes referred to as synthetic aviation fuel, is low-carbon biofuel produced by converting biomass feedstocks — such as crops, waste oils, and captured gases — into jet fuel.
SAF can be used alongside traditional jet fuel without modifications to aircraft or infrastructure, and it has already been used in hundreds of thousands of flights worldwide.
This article explores the fundamentals of SAF — how it’s made, how it’s used, and what its future holds.
How Is SAF Made?
SAF can be produced through a variety of methods, often called technology pathways. Seven direct technology pathways have been certified by the global standard-setting organization ASTM, but three are the most common today: hydroprocessed esters and fatty acids (HEFA), alcohol to jet (AtJ) and power to liquid (PtL).
- Hydroprocessed Esters and Fatty Acids (HEFA): SAF made via the HEFA pathway is refined from agricultural products like waste oils, animal fats, and vegetable oils. HEFA removes oxygen from the feedstock molecules, replacing it with hydrogen. The molecules are then transformed to match the structure of jet fuel.
- Alcohol-to-Jet (AtJ): With AtJ, sustainable aviation fuel is made from ethanol sourced from corn, sugarcane, related crops, or waste. Fermentation first converts the feedstock into sugars, and the sugars are then converted to SAF.
- Power-to-Liquid (PtL): The PtL pathway captures carbon dioxide and synthesizes it with green hydrogen (i.e., hydrogen produced using renewable energy) to make SAF.
These pathways are all at different stages of commercial availability, as summarized below. You can learn more about these three production technologies in our SAF 101: Production Technologies article.
| Pathway | Feedstock | Technology Status |
| HEFA | Oil crops, used cooking oil, other waste fats | Mature Commercial Scale |
| Alcohol-to-Jet (AtJ) | Corn, sugarcane, cellulosic biomass | Commercial Scale |
| Power-to-Liquid (PtL) | Carbon dioxide (CO2), hydrogen (H2) | In Development |
Source: U.S. Department of Energy, Alternative Fuels Data Center
SAF and Carbon Intensity
SAF’s carbon intensity score (CI) refers to the greenhouse gas emissions produced per unit of fuel. The particular production technology and feedstock used to make SAF influence the fuel’s carbon intensity, so not all SAF has the same CI. Carbon intensity is calculated using agreed-upon carbon accounting methods that examine every stage of the SAF life cycle.
- HEFA SAF can cut emissions by up to 85% compared with traditional jet fuel.
- AtJ SAF can reduce emissions by up to 94%, but upstream emissions and land use factors may diminish the overall CI advantage of corn-based ethanol.
- PtL SAF has the highest reduction potential, lowering emissions by up to 99% when produced with green hydrogen and captured CO2. (While the emissions reduction potential of PtL makes it an attractive option, PtL SAF could cost as much as eight times more than HEFA due to the cost of infrastructure and green hydrogen, as well as the availability of captured CO2.)
The Benefits of SAF
SAF offers new opportunities for farmers, helps diversify our energy portfolio, and significantly reduces emissions. As a complement to traditional jet fuel, SAF helps meet growing aviation demand while reducing emissions. Among its economic benefits, SAF creates new revenue streams for farmers, who can grow feedstock crops, some of which improve soil quality. SAF production also creates well-paying industrial jobs.
Most importantly, depending on how it’s made, SAF can reduce life-cycle emissions by more than 80% compared with conventional jet fuel while also cutting pollution from particulates, sulfur oxides (SOx), and nitrogen oxides (NOx), leading to cleaner air and water.
How Is SAF Used Today?
Right now, sustainable aviation fuel is used in small quantities by most major airlines and cargo companies in the United States and around the world, including United Airlines, KLM, and DHL. SAF is currently approved by the FAA for commercial use in blends of up to 50% with traditional jet fuel. In 2023, Gulfstream completed the world’s first transatlantic flight using 100% SAF from World Energy, followed shortly thereafter by Virgin Atlantic’s first transatlantic flight, both demonstrating the viability of 100% SAF for long-haul flights.
Unlocking the Full Value of SAF
Airlines aren’t the only ones who can benefit from sustainable aviation fuel. Companies like Microsoft and BCG are leveraging SAF certificates (SAFc) to reduce their Scope 3 emissions from business travel or freight transport. SAF certificates allow companies to claim emissions reductions even if they don’t directly purchase the fuel, enabling broader participation in aviation decarbonization.
With SAFc, the fuel’s environmental attributes are decoupled from the physical fuel and sold as a separate product. This enables companies to purchase, transparently track, and claim the emissions benefits of sustainable aviation fuel regardless of their industry or location. This allows the world’s leading companies to meet their decarbonization goals while increasing SAF demand and use, even though they don’t buy the physical fuel themselves.
The Future of SAF
Demand for SAF is growing, but we need more of it. SAF represented just 0.2% of global jet fuel use in 2023. Scaling up SAF production is crucial to meeting clean energy needs.
For more than two decades, World Energy has been at the forefront of the advanced biofuels industry, and we are committed to helping the industry scale. We led the way as the world’s first commercial-scale producer of sustainable aviation fuel, and we’re continuing to push the boundaries of what’s possible with SAF. As the industry and its technologies grow and evolve, World Energy will be there to help guide our customers, partners, and the industry toward its future.
