GCMD Outlines Practical Approach to Quantity Assurance in Marine Biofuel Supply Chains

The Global Centre for Maritime Decarbonisation (GCMD) has released a new report, Quantity Assurance in Marine Biofuel Supply Chains, outlining a practical approach to help shipowners verify they are receiving both the total fuel volume and the renewable content they contracted for. The findings draw on evidence from GCMD’s end-to-end marine biofuel supply chain trials conducted under commercial operating conditions.

Why does quantity assurance matter for marine biofuels?

Biofuels are purchased not just for their energy content but for the renewable content and emissions reductions they represent. That renewable fraction determines the green premium buyers pay and underpins both GHG accounting and regulatory compliance. Yet blend ratios such as B24 or B30 are typically declared by suppliers rather than independently verified, leaving a verification gap that GCMD’s report aims to help close.

How can shipowners verify the total quantity of fuel transferred?

Mass flow meters (MFMs) have become the preferred method for custody transfer, offering a transparent and auditable basis for measuring fuel quantity. However, the report flags a technical wrinkle: adding fatty acid methyl ester (FAME) to conventional marine fuels such as VLSFO or HSFO can lower the viscosity of the final blend, potentially pushing it outside the validated operating range of the MFM installed on the bunker barge. To preserve measurement integrity, GCMD recommends assessing the final blend’s viscosity under actual transfer conditions against the applicable MFM range, managed either through transfer-temperature control or by using MFMs validated for broader operating ranges.

How is the renewable fraction in biofuel blends verified?

Verification methods differ by fuel type. FAME-based blends can be checked through compositional analysis, while hydrotreated vegetable oil (HVO)-based blends require radiocarbon analysis, since renewable and fossil hydrocarbons in HVO cannot be distinguished through compositional testing alone.

Interpreting these results, however, is not straightforward. Neat FAME can contain up to 3.5% non-ester material, meaning the measurable FAME content of a finished BXX blend may not exactly match its declared blend ratio. Laboratory testing also carries finite measurement precision, so a gap between a measured result and a declared blend ratio does not automatically indicate incorrect blending or under-delivery.

How does this fit into GCMD’s broader biofuels assurance work?

The report completes GCMD’s three-pillar quality, quantity, and GHG emissions abatement assurance framework for marine biofuels, addressing in turn whether a fuel is fit for use, whether it delivers its claimed emissions reductions, and whether it contains the contracted fuel quantity and renewable content.

Professor Lynn Loo, CEO of GCMD, said buyers need confidence that they have received both the fuel and the renewable content they paid for, and that the report provides a practical, evidence-backed basis for verifying renewable fuel claims, protecting commercial value, and supporting credible GHG accounting as marine biofuel use scales.