When we use a book and claim as a tool for sustainable procurement, how do we ensure that we are receiving the correct environmental attributes? This data often underlies an important carbon reduction benefit, so how can we ensure the claim is credible and accurate? Especially in complex supply chains, we lean on sustainability certification systems to establish and track the sustainability profile of the fuels, ensuring that each party along the chain of custody has met specific sustainability criteria and implemented the correct calculation methods.

Certification systems reference chain of custody models—or approaches for tracking the lifecycle of a product. A model called “mass balance” is particularly common for transportation fuel supply chains. In short, mass balance helps us define product outputs when physically mixing inputs. A mass balance chain of custody model is key for tracking a fuel’s sustainability profile, particularly when infrastructure makes it necessary—or where it’s more efficient—to mix feedstocks in a production process or blend fuels before delivery. Mass balance allows a sustainable fuel to be tracked and audited as a proportion of a volumetric total, ensuring its environmental impact without requiring the purchaser to physically isolate and directly consume the lower-carbon fuel in order to claim its attributes.

Note that book and claim is a similarly flexible model, but even more so—it allows for the environmental attributes to be completely decoupled from the underlying fuel volume and claimed elsewhere. Correct use of mass balance, then, helps enable subsequent practitioners, such as a registry operator, to correctly track and trace the sustainability profile of the solution, or an emission reporter, to correctly account for and allocate the emission profile of the fuel. An emerging best practice for transport book and claim systems is to require mass balance certification of the physical fuel supply chain, when applicable, as a prerequisite to the book and claim step.

This ensures the supply chain demonstrates specific sustainability characteristics before decoupling the environmental attributes. It is important to note that mass balance is not the only chain of custody model for tracking the environmental attributes of a transport fuel. Other chain of custody models that evaluate physical supply chains similar to mass balance, include, in increasing order of stringency about the level of mixing:

• controlled blending
• segregated
• identity preserved.

Learn more about the underlying elements of mass balance and these additional models in ISO 22095(2020). Or, for more information about how mass balance plays a role in your supply chain, we encourage you to explore existing certification schemes for your industry. Additional information may also be available from your fuel provider, certifier, or registry operator. A few scheme examples include: Aviation: RSB CORSIA, ISCC CORSIA, RSB EU RED, ISCC EU, RSB Global, ISCC Plus Maritime Fuels and beyond: ISCC Plus, RSB Global, ISCC EU, RSB EU RED