CHAIN-OF-CUSTODY ALLOCATION RULES

Chain-of-custody allocation rules determine who can claim a removal when carbon passes through several companies or mixes with other carbon in shared facilities. Governments and certification-scheme owners specify how operators record incoming quantities, processing losses, transfers and final storage. A direct-air-capture company using a pipeline that also carries fossil CO₂, for example, needs an accepted way to demonstrate how much atmospheric CO₂ reached storage without following individual molecules. Clear allocation rules allow such projects to share infrastructure and sell an identifiable removal benefit, while preventing different parties from selling or claiming that same benefit twice. The rules may require physical separation, permit controlled mixing or allow separately traded environmental claims within defined limits.

Each allocation method offers different flexibility and needs different checks. Physical separation keeps a qualifying material apart throughout the supply chain. Mass balance allows mixing but requires records showing that claimed outputs do not exceed qualifying inputs after losses. Book-and-claim allows an environmental benefit to be bought separately from the physical product; the rules must specify when that separation supports the intended claim. For CDR, all methods need evidence of atmospheric origin and net storage, agreed geographical and time limits, and a record of which party uses the removal claim. Reporting a removal in a national inventory and issuing a credit are not automatically incompatible: the relevant rules must distinguish overlapping reports from competing claims to the same benefit.

Accepted allocation methods can let small removal projects use existing pipelines, processing plants and storage facilities instead of building separate systems to preserve physical separation. Buyers can see which stored quantity and environmental benefit their contract gives them, even when several firms handle the carbon. Common records and recognised checks can reduce repeated investigations and negotiations between suppliers. Experience from renewable-fuel supply chains provides useful administrative models. Applying them to removals still requires an explicit account of atmospheric origin, emissions and losses, since tracing a fuel's sustainability credentials does not establish that carbon has been removed and durably stored.

A company may sell a claim that cannot be reconciled with the qualifying carbon entering or remaining in the system. Missing records, ignored processing losses and incompatible databases can make such errors difficult to detect. Separately traded claims can also imply that a buyer received a physical product or service that was actually delivered elsewhere. Rules that permit this separation must define what the buyer may say and prevent another party from using the same benefit. Excessively restrictive rules create a different problem: they can require unnecessary physical segregation and make shared infrastructure unusable for otherwise eligible removals.

Auditors should compare claimed quantities with recorded inputs, outputs and losses, including transfers between companies and certification schemes. Regulators and scheme owners should track missing records, late reconciliation, duplicate claims and transactions rejected because systems cannot exchange information. Recurring problems should lead to corrected records, better data exchange or restrictions on the affected allocation method.

Regulators and scheme owners should decide which allocation methods support the claims their programmes allow. Infrastructure operators and suppliers can test whether the required flow and storage records are practical. Registry operators and auditors should check that transactions remain verifiable as carbon changes hands. National inventory teams can identify reporting overlaps, while buyers and consumer representatives test whether the final claim accurately describes what has been purchased.

International schemes can set allocation requirements for their participants. Supranational, national and state regulators can require particular methods in compliance markets, while industry standards and private certification schemes can govern contractual supply chains. These bodies implement the lever by deciding which quantities and claims their systems recognise and enforcing the associated recordkeeping. Municipal buyers and philanthropies ordinarily use those recognised methods when purchasing; that purchasing role alone does not establish the allocation system.