The Global Centre for Maritime Decarbonisation (GCMD) has warned that blending FAME (fatty acid methyl ester) into conventional marine fuel can lower the resulting blend’s viscosity enough to push it outside the validated operating range of a bunker barge’s mass flow meter (MFM), according to a new report from the centre released on Wednesday.
The report, titled Quantity assurance in marine biofuel supply chains, marks the completion of GCMD’s three-pillar biofuel assurance framework, which also covers fuel quality and greenhouse gas emissions abatement, as reported by Ship & Bunker.
Calibration Ranges Under Scrutiny
According to GCMD, an MFM’s applicable measurement range depends on the conditions under which it was calibrated and validated. As an example, the centre notes that an MFM fitted to a barge predominantly supplying residual fuels such as RMG 380 may only be validated across a viscosity range of roughly 30-150 mm²/s.
GCMD explains that while a meter may be technically capable of reading fuels below this range, using a lower-viscosity blend would fall outside the barge’s approved operating envelope unless the MFM system has been separately calibrated, validated, and approved to cover that broader range.
Declared Ratios Not Independently Verified
The report also flags that commonly used blend ratios, such as B24 or B30, are typically declared by the supplier rather than independently verified, Ship & Bunker reports. GCMD notes that under-reporting of blend ratios carries consequences for GHG accounting and compliance, since the renewable fraction of a blend determines its green premium.
To manage this risk, GCMD recommends that the final blend’s viscosity be checked against the meter’s validated range under actual transfer conditions, either through temperature control during transfer or by using MFMs validated for wider viscosity ranges.
The centre further cautions against over-interpreting laboratory test results, pointing out that neat FAME can contain up to 3.5% non-ester material, and that testing methods have limited precision. As such, a measured result that diverges from a declared blend ratio does not automatically indicate under-delivery, GCMD says.
“Buyers need confidence that they have received both the fuel and the renewable content they paid for,” said GCMD CEO Lynn Loo, as quoted in the report.
According to the report, biofuel bunkering volumes in Singapore and Rotterdam rose from negligible levels in 2020 to nearly two million metric tonnes in 2025.
Does This Matter To You?
As biofuel blends become a more common bunkering option, verifying that delivered volumes are accurately measured is becoming a practical concern. Parties involved in bunkering transactions involving FAME blends may need to confirm that the barge’s MFM has been calibrated for the viscosity range of the specific blend being supplied, not just for conventional fuel grades.
Given that blend ratios are often supplier-declared rather than independently verified, according to GCMD, buyers relying on the renewable content of a delivery for compliance or cost purposes may want to understand how that ratio was determined and whether it has been checked against actual transfer conditions.
Gulf Bunkering does not provide operational or security guidance. This article is for informational purposes only. Operators should consult flag state authorities, P&I clubs, and relevant advisories for decisions relating to transit planning.
Sources: Ship & Bunker, Global Centre for Maritime Decarbonisation (GCMD)
