Marine fuels that pass routine ISO 8217 testing are increasingly triggering onboard failures linked to instability, incompatibility and unconventional blend components, according to Lloyd’s Register.
LR’s FOBAS Fuel Quality Report for the first half of 2026 found that off-specification fuels remained a persistent problem, but some of the most disruptive cases involved products that met standard compliance limits.
Several vessels experienced operational difficulties in March and April after bunkering at a major fuel hub. Forensic testing found elevated concentrations of Estonian shale oil in many samples, estimated at around 10-15% in some cases.
ISO 8217 permits shale oil as a blend component, but FOBAS linked higher concentrations to fuel instability and problems affecting filters, separators and fuel pumps. Off-specification cases remained elevated throughout the first six months of 2026.
The most frequent problems included sulphur exceedances, excessive water, sediment and stability issues, elevated catalytic fines, sodium contamination and low flash points in distillate fuels.
Biofuels, particularly FAME blends, were not a primary source of quality problems. Where blended fuels caused difficulties, the conventional very low sulphur fuel oil component was generally responsible rather than the FAME fraction.
LR said operators will need to focus more closely on fuel stability, compatibility and composition as marine fuels become more diverse and risks become harder to detect through routine pass-or-fail testing.
“The findings from our latest report show that fuel quality risk is evolving. The challenge is no longer simply identifying fuels that fail specification. Increasingly, operators are encountering fuels that meet the required limits but still create operational difficulties once they are stored, handled and used onboard,” LR fuel specialist consultant Murray Kirkwood said. “As fuel blending becomes more complex, the distinction that matters is increasingly not between on-spec and off-spec fuel, but between fuels that are operationally resilient and fuels that are operationally fragile. Understanding that difference is becoming essential for shipowners and operators.”
Lloyd’s Register is a maritime professional services organisation providing classification, compliance, technical assurance and advisory services. Its Fuel Oil Bunker Analysis and Advisory Service combines routine fuel testing with forensic investigation of operational incidents.