Lloyd’s Register (LR) has warned that ship operators face a growing challenge from marine fuels that pass routine ISO 8217 compliance testing but still cause operational problems once on board.

The findings, published in the latest fuel quality report by LR's Fuel Oil Bunker Analysis and Advisory Service (FOBAS), draw on thousands of fuel samples analysed between January and June 2026, alongside investigative testing and incident analysis. While off-specification fuels remain a persistent challenge, the report states that some of the most disruptive cases now involve fuels that meet specification limits but exhibit poor stability or compatibility, or contain non-conventional blend components identifiable only through more detailed forensic analysis.

One case highlighted in the report involved vessels bunkering at a major hub during March and April, with subsequent forensic testing revealing elevated concentrations of Estonian shale oil in the fuel — in some cases estimated at around 10–15%. Although shale oil is recognised within ISO 8217 as an acceptable blend component, FOBAS investigations found that higher concentrations can be associated with fuel instability and operational issues affecting filters, separators and fuel pumps.

Off-specification cases remained elevated throughout the first six months of the year. The most common recurring issues included sulphur exceedances, excessive water content, sediment and stability problems, elevated catalytic fines, sodium contamination and low flash point distillate fuels.

On biofuels, the report notes that FAME blends continued to grow in use without emerging as a primary source of quality problems. Where issues occurred in blended fuels, they were generally associated with the conventional very-low-sulphur fuel oil (VLSFO) component rather than the FAME fraction.

Murray Kirkwood, fuel specialist consultant at Lloyd’s Register, stated: “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 on board.

“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.”

The report concludes that, as the marine fuel supply becomes more diverse, operators will need to place greater emphasis on understanding fuel stability, compatibility and composition, rather than relying solely on pass-or-fail specification testing to manage quality risk.