SAF is fuel produced from non-fossil fuel sources that can result in lower greenhouse gas (GHG) emissions than conventional jet fuel on a lifecycle basis. As a fully certified drop-in fuel when blended with conventional jet fuel in accordance with industry standards, SAF is compatible with existing infrastructure. Because the use of SAF in the place of conventional jet fuel has the potential to reduce lifecycle GHG emissions and does not require any modifications to infrastructure or aircraft, it's crucial for decarbonizing aviation in the short- and medium-term. SAF plays an important role in Southwest’s environmental sustainability plan and path to achieve net zero carbon emissions by 2050. By 2030, we plan to replace 10% of our total jet fuel consumption with SAF.

How is SAF produced?

While traditional jet fuel is made from fossil fuels extracted from the earth, SAF is made from a variety of alternate resources, also known as “feedstocks,” and is produced through various technologies, also known as “processing pathways.” The different feedstocks include:

• Fats, oils, greases (FOGs), which can come from used cooking oil and tallow, energy or cover crops like willow wood and switchgrass, and edible oil crops like corn. Most of the SAF commercially available today comes from used cooking oil or tallow.
• Other biomass sources, which include forestry and agricultural residues as well as municipal solid waste.
• Carbon captured directly from the atmosphere, also known as direct air capture (DAC), which is non-biomass based. Fuel made through a process involving renewable energy, carbon DAC, and green hydrogen is generally referred to as power-to-liquid (PtL), synthetic fuel (synfuel), and / or e-fuel.

As for the processing pathways, there are several approved for converting feedstocks into SAF, including:

• Hydroprocessed Esters and Fatty Acids (HEFA), which converts FOGs into jet fuel. This is the most common pathway used today.
• Alcohol-to-jet (ATJ), which converts ethanol or isobutanol made from biomass into jet fuel.
• Gasification / Fischer-Tropsch (FT), which converts biomass into jet fuel. FT can also be used to convert carbon from DAC into jet fuel (PtL or e-Fuel).

Further, SAF can be produced without extensive infrastructural changes via co-processing, which is the simultaneous processing of fuels using non-petroleum and petroleum feedstocks at existing fuel refineries. As SAF development and adoption grows, feedstocks and production technologies will evolve.

How does SAF reduce emissions?

The production of conventional jet fuel requires the extraction of fossil fuel, and so when conventional jet fuel is used, it results in a release of carbon that has been sequestered in the ground for millions of years. All commercially produced SAF on the market today leverages biogenic feedstocks (biomass). On the other hand, biomass is composed of carbon that has been removed from the atmosphere on a comparatively short timescale, and so the carbon released from SAF during combustion (i.e., flying on it) reflects a “recycling” of carbon as opposed to a release of “new” carbon. In short, using SAF reduces net carbon emissions by replacing a fuel with higher lifecycle emissions with one with lower lifecycle emissions. It is important to note that the emission reduction benefits will vary across feedstock types and SAF production processes.

What are SAF environmental attributes?

“Environmental attributes” refer to the quantified environmental benefits associated with the use of SAF, as compared to the use of traditional jet fuel. Environmental attributes are tracked, purchased, and claimed separately from the physical SAF they are associated with. This process of tracking, purchasing, and claiming environmental attributes separately is part of a broadly accepted methodology of SAF accounting called “book and claim.” There are entities and individuals who wish to support and to benefit from the use of SAF, but are not connected to the physical fuel supply chain and thus not able to decide which physical fuel gets used in their services or operations. Within this context, book and claim enables individuals or entities to support SAF by purchasing environmental attributes, and to make an associated “claim” to the environmental benefit those attributes represent. In a corporate context, the purchase of environmental attributes may factor into corporate carbon accounting. In a consumer context, the purchase of environmental attributes provides a vehicle for supporting SAF and both demonstrates demand and helps to cover the cost difference between SAF and traditional jet fuel.