The Future of Sustainable Aviation Fuel

Mass Balance vs. Book & Claim in Chain of Custody Fuel ( SAF )

In the journey to net-zero aviation, Sustainable Aviation Fuel (SAF) stands as the leading solution for decarbonizing flights. But how SAF is tracked, claimed, and accounted for in emissions reporting is equally critical. Enter two Chain of Custody (CoC) models—Mass Balancing and Book & Claim. Each model brings unique strengths, challenges, and strategic benefits, helping drive SAF adoption across airlines, corporations, and regions worldwide. Curious about how these CoC models power the future of sustainable flight? Let’s dive in.

1. The Role of Chain of Custody in SAF Adoption

SAF’s potential to replace fossil-based jet fuels hinges on not only its production but on how its use is documented and accounted. This accountability comes through Chain of Custody (CoC) models, which verify and track SAF’s environmental benefits. Here, two prominent methods—Mass Balancing and Book & Claim—allow for flexibility and reliability in emissions reporting, making SAF accessible across diverse regions and market participants.

2. Understanding Mass Balance and Book & Claim

Both models enable aviation stakeholders to claim the environmental benefits of SAF, but they differ in how these benefits are attached to SAF’s physical fuel molecules and emissions reporting requirements. Let’s look at each in detail:

Mass Balancing: Direct Emissions Reduction for Scope 1

Mass balancing physically tracks SAF from the point of blending with fossil jet fuel to the aircraft. Here, the environmental attributes of SAF (like emissions reductions) remain tied to its physical molecules, making mass balancing a robust way to demonstrate direct emission reductions for airlines. This method works especially well for meeting Scope 1 emissions goals, which include direct emissions from sources owned or controlled by an airline.

How Mass Balancing Works:

• SAF feedstocks are certified before entering production and blending.
• A recorded proportion of SAF is physically blended with conventional jet fuel.
• The environmental benefits are proportionally assigned to airlines that receive this SAF at specific locations, based on the blended SAF ratio.

Example:
If 10% of SAF is blended with 90% conventional fuel, the airline can claim the environmental benefit of that 10% SAF blend for its Scope 1 emissions.

Benefits of Mass Balancing:

• Assurance of Physical SAF Use: Airlines using mass balancing can confirm that the SAF blend powers their flights, which is crucial for direct emissions reduction.
• Compliance with Regulatory Blending Targets: Many regulatory bodies set SAF blending targets, and mass balancing supports airlines in meeting these mandates at major hubs.

Challenges:

Scalability: As SAF demand grows, the ability to distribute it widely while maintaining mass balancing becomes challenging.

Limited Availability and Higher Costs: SAF isn’t available at every airport, limiting airlines to specific locations for SAF usage. The need to physically transport SAF to each airport also drives up costs.

3. Book & Claim: Expanding SAF’s Reach for Scope 2 and Scope 3

Unlike mass balancing, the Book & Claim model separates SAF’s environmental attributes from its physical molecules, allowing airlines, corporations, and even logistics providers to buy SAF benefits (like emissions reductions) even if they can’t physically access SAF. This model is key for Scope 2 and Scope 3 emissions, covering indirect emissions from the purchase of goods and services and from activities not directly controlled by the airline.

How Book & Claim Works:

• SAF producers blend SAF with traditional fuel at a single facility and record its environmental attributes in a digital registry.
• Airlines, corporations, or other stakeholders buy these environmental attributes (often called SAF credits or certificates) without taking physical delivery of the SAF.
• The attributes are “booked” to the buyer, allowing them to claim emissions reductions in their environmental reporting.

Example:
A corporate buyer might purchase a Book & Claim SAF credit to offset emissions for business travel, even if they don’t have access to physical SAF at their location.

Benefits of Book & Claim:

• Global Accessibility: Book & Claim enables organizations in regions without SAF production to participate in decarbonization efforts, broadening SAF’s market and demand.
• Cost-Effective and Logistically Simple: This model eliminates the need to physically transport SAF, reducing distribution costs and associated emissions.

Challenges:

Credibility and Double-Counting Risks: Book & Claim relies heavily on digital registries and robust tracking to ensure that each environmental claim is unique and accurately reflects SAF’s usage. Multiple layers of verification are required to prevent double-counting of emission reductions.

4. Why Both Methods Are Essential for Scaling SAF

While these CoC methods differ significantly, they complement each other in building a sustainable future for aviation. Here’s how they work together:

Flexibility for Stakeholders: With Book & Claim, companies in remote or SAF-limited regions can still engage in SAF programs, boosting demand and encouraging further investment in SAF production.

Broad Emissions Impact: By using both Mass Balancing and Book & Claim, SAF’s benefits reach both Scope 1 (direct) and Scope 2 and 3 (indirect) emissions, allowing airlines and corporations to make impactful, credible environmental claims.

Encouraging Market Demand: Mass Balancing supports physical SAF distribution at high-traffic airports, whereas Book & Claim enables demand from corporate travel, logistics, and regional markets that otherwise couldn’t access SAF.

5. Key Takeaways: The Future of SAF Adoption

1. Enhanced Global Reach: Book & Claim enables SAF adoption beyond the physical limitations of SAF infrastructure, making it possible for international companies to align with their carbon reduction commitments.
2. Meeting Diverse Emission Goals: Mass balancing directly addresses Scope 1 emissions, aligning with airlines’ regulatory compliance, while Book & Claim supports Scope 3 reductions, which is particularly useful for corporate ESG goals.
3. A Transparent Path Forward: As Book & Claim methods expand, digital registries and third-party auditing are critical to ensuring accurate emissions claims, mitigating double-counting, and boosting market confidence.

Conclusion

SAF’s journey to mainstream adoption, Mass Balancing and Book & Claim aren’t competitors; they’re allies. Mass Balancing allows airlines to meet regulatory and compliance standards, physically using SAF to reduce Scope 1 emissions. Book & Claim, on the other hand, democratizes SAF’s benefits by enabling corporations and regions without SAF access to still participate in emissions reductions.

Together, these CoC models provide a holistic, scalable solution for aviation’s future. As SAF infrastructure grows, the industry can lean on both methods to ensure sustainability claims remain credible, verified, and impactful. For airlines, corporations, and stakeholders across the aviation value chain, embracing both CoC models is a practical step toward achieving a truly sustainable future in air travel.