Your guide to understanding key terms and concepts within the SAF landscape
There are numerous technical terms and concepts within the sustainable aviation fuel (SAF) landscape. To understand how the aviation industry is working towards wide-scale emissions reduction, we put together a guide that breaks down commonly used language across the lower-carbon fuel value chain to help you navigate this topic.
Sustainable aviation fuel (SAF)
SAF, also known as an alternative jet fuel, is made from renewable resources (feedstocks) like waste oils, agricultural residues, or other biomass. It’s typically blended with fossil jet fuel and used as a “drop-in” substitution, meaning it works in existing aircrafts today without modifications and can be distributed alongside traditional jet fuel our using current fuel infrastructure.
SAF has the potential to significantly reduce the carbon intensity of flying. SAF contains the same amount of hydrocarbons as traditional fossil-derived jet fuel — meaning that when burned, SAF produces similar levels of carbon dioxide as conventional aviation fuel. However, the emissions released when SAF is burned are already part of an emissions life cycle and are not extracted from the ground specifically for creating aviation fuel. On the other hand, the production of conventional jet fuel requires extraction of fossil fuel, resulting in a release of carbon that has been sequestered for millions of years. Therefore, using SAF results in a life-cycle reduction in emissions as compared to the conventional jet fuel it replaces.
What SAF means for decarbonizing aviation: SAF is a key tool in reducing aviation emissions. It is available for use today but in very limited quantities. While challenges remain for SAF to be scaled effectively, the industry is working to unlock its potential.
Life-cycle emissions (Life-cycle assessment (LCA))
Life-cycle emissions refer to the total greenhouse gas (GHG) emissions generated during a service, product, or process’ life cycle, from production to disposal. A life-cycle assessment (LCA) is the process of evaluating a product’s environmental impact from raw material extraction to waste management — and is commonly referred to as a “cradle-to-grave” analysis.
What LCAs mean within the SAF landscape: A LCA helps measure SAF’s climate impact by assessing emissions from feedstock cultivation, processing, transportation, and combustion. This comprehensive overview is crucial for validating SAF’s environmental benefits as compared to fossil fuels.
Offtake agreement
An offtake agreement is a contract through which a producer (or seller) agrees to sell and a buyer agrees to purchase a certain amount of product under specified, agreed upon terms. Offtake agreements typically provide short-term pricing (in the case of aviation, a static premium price that follows global jet fuel pricing) or long-term pricing (a dynamic price that follows an index).
What offtake agreements within the SAF landscape: Offtake agreements create long-term demand and investment by securing future supply for the purchaser and contracted demand for the producer/seller. This helps derisk the industry and encourage the scaling of essential SAF production.
Certifications for SAF
Today, there are two bodies providing sustainability certifications for sustainable aviation fuel:
- The International Sustainability and Carbon Certification (ISCC)
- The Roundtable on Sustainable Biomaterials (RSB)
Both ISCC and RSB certification schemes are recognized by the International Civil Aviation Organization (ICAO) and the certification schemes vary to align with compliance obligations for ICAO’s Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA), the European Union Renewable Energy Direction (EU RED), and the voluntary market.
What certifications for SAF mean within the SAF landscape: These certifications and certifying bodies create standards for the way the industry uses and understands SAF. The certifications ensure sustainability in feedstock production, traceability of sustainable materials through the supply chain, and verified reduction of greenhouse gas emissions.
Environmental attributes
Environmental attributes are the climate benefits or reductions associated with the use of a lower-carbon product.
What environmental attributes mean within the SAF landscape: Environmental attributes allow for the measurement and understanding of the climate benefits of alternative jet fuel like SAF.
Environmental attribute certificates (EACs) or SAF certificates
Environmental attribute certificates (EACs) are instruments to quantify and track the climate benefits of a decarbonization product or action. Within the context of lower-carbon jet fuel and aviation, EACs are sometimes known as “SAF certificates,” and in this case, they quantify the environmental benefits associated with physical SAF. These attributes verify the production and use of SAF, and can be bought, sold, and claimed, often separately from the physical product.
What these certificates mean within the SAF landscape: SAF has two components: the physical fuel and the environmental attributes associated with it. In a chain of custody model, buyers can purchase and “claim” these attributes in the context of their emissions reporting. This enables broader participation in reducing emissions across the aviation value chain, including by entities who are not connected directly to the physical fuel supply chain (i.e., corporate travelers). Once environmental attributes are “retired,” SAF certificates are issued — essentially evidencing that the “claim” representing the attribute has been used.
Retiring environmental attributes
Retiring environmental attributes refers to the permanent removal from circulation of the environmental benefits represented by a SAF certificate, which allows these benefits to be claimed and “retired.”
What retirement means within the SAF landscape: Once a SAF certificate or attribute is retired, the environmental benefits, such as the associated emissions reductions, can no longer be sold or traded. This promotes transparency in sustainability reporting and avoids double-claiming of environmental benefits.
Chain of custody (CoC)
A chain of custody (CoC) accounting model tracks a product and its associated information or attributes through each step of the value chain, ensuring transparency and accountability. The primary chain of custody models leveraged within the SAF market today are “book and claim” and “mass balance.”
What CoC means for aviation decarbonization: Chain of custody systems ensure SAF’s quality and climate claims, building trust that the fuel delivers on its sustainability promises and that the associated attributes are traceable and auditable. Chain of custody models are what provide the infrastructure that allows purchasers across the value chain to help support the nascent SAF industry by purchasing SAF environmental attributes.
Book and claim
A book and claim chain of custody model separates environmental attributes from the associated physical product (i.e., fuel), allowing the attributes to be bought and traded independently of the physical fuel.
What book and claim means within the SAF landscape: After a volume of physical SAF’s environmental attributes has been verified, the attributes can be sold and tracked (either bundled with the physical fuel itself or claimed separately from the physical fuel) through book and claim. This separation supports SAF growth and is essential for scaling SAF globally. By allowing for purchases across the value chain and broader enablement of emissions reduction in aviation, book and claim opens a pathway for further SAF ”usage,” especially in locations where physical SAF is not available.
Mass balance
A mass balance chain of custody model tracks certified materials (i.e., SAF molecules) as it moves along the value chain, ensuring the inputs match the outputs. In a mass balance model, certified materials are mixed with materials without that specific set of characteristics, but the quantity and proportion of the certified materials in the blend are tracked and maintained.
What mass balances means within the SAF landscape: A mass balance system ensures that the total claimed volume of SAF matches the amount produced and blended with conventional fuel, maintaining the integrity of sustainability claims and allowing for SAF to be traced and auditable throughout the value chain.
Scope 1 emissions
Scope 1 emissions, as defined by the Greenhouse Gas Protocol, are direct greenhouse gas emissions from sources owned or controlled by an entity or organization.
How scope 1 emissions relate to aviation decarbonization: For airlines, this includes emissions from direct fuel burn, as well as other emissions associated with flying an airplane — from takeoff to landing.
Scope 3 emissions
Scope 3 emissions, as defined by the Greenhouse Gas Protocol, are indirect greenhouse gas emissions that occur within an entity or company’s value chain, including upstream and downstream activities.
How scope 3 emissions relate to aviation decarbonization: An airline's scope 3 emissions may include SAF production, transportation, and related services; whereas for travelers, scope 3 emissions may include travel from flights. Note: An airline’s scope 1 emissions can be a traveler’s scope 3 emissions.
Sustainable Aviation Fuel registries
There are multiple registries that track SAF attributes, ensuring their environmental claims are accounted for and accurate. Today, major registries include:
- SAFc Registry by Rocky Mountain Institute (RMI)
- Roundtable on Sustainable Biomaterials (RSB)
- International Sustainability and Carbon Certification (ISCC)
- Avelia (Shell)
- Coming soon: IATA
Registries validate transactions and the authenticity of the SAF, maintaining and tracking chain of custody across the value chain.
What SAF registries mean within the SAF landscape: Registries help establish transparency and consistency across SAF transactions while also validating and authenticating SAF. This ensures that environmental benefits are not double-claimed and that sustainability claims are credible.
