Latest FOBAS report provides fuel for thought

The second half of 2025 saw a worrying rise in the frequency and severity of marine fuel quality challenges, reports Samantha Andrews

Somewhere at this very moment, at least one vessel is taking on fuel bunkers. But when that fuel is contaminated and/or off-specification, the consequences can range from the inconvenient to the catastrophic. Filters clog, purifiers become overwhelmed, and engines run inefficiently. In the worst cases, vessels lose propulsion altogether, posing a serious safety risk.

Lloyd's Register's Fuel Oil Bunker Analysis and Advisory Service (FOBAS) has been tracking marine fuel quality for years. The latest edition, the FOBAS Fuel Quality Report for the second half of 2025, offers both good news - and bad.

The good news is that around "96% of the fuels comply with ISO 8217 [the international benchmark for marine fuel quality] requirements," says Dr Muhammad Usman, a product manager at Lloyd’s Register, who sits on the ISO working group that develops the standard and on the CIMAC fuels working group.

The bad news is that the second half of 2025 was, as the report says, “marked by a notable escalation in both the frequency and severity of fuel quality challenges across the global marine sector.”

The residual fuel picture

The FOBAS report covers four parameters for residual-based fuel oils, sulphur outliers, catalytic fines, total sediment, and acid number.

International regulations limit sulphur content in marine fuels (outside ECA-Sox zones) to 0.50% by mass, unless the ship is fitted with an exhaust gas cleaning system. During the second half of 2025, sulphur outliers were reported in major hubs, including Rotterdam. For ships without exhaust cleaning systems, options are severely limited. De-bunkering is often the only solution.

Catalytic fines – abrasive aluminium and silicon particles – can cause significant wear on fuel pumps and injectors. The second half of 2025 saw more frequent and severe breaches than the first half. Incidents include one in Singapore in December, where levels reached 580 mg/kg – an incident that Usman describes as “a technical safety issue."

Total sediment levels present a continuing challenge, usually related to the stability of asphaltenes – heavy molecular compounds present in residual fuel. When asphaltenes drop out of suspension, they cause sludging in storage tanks, purifiers and filters. In extreme cases, they can choke the entire onboard fuel system. Antwerp recorded the highest average sediment values among major bunkering ports in the period.

Acid number is an indicator of corrosive potential but requires careful interpretation. Elevated readings may represent naturally occurring acidic components unlikely to cause operational issues, but an unusually high result from a port known for low acid number fuels should be investigated. Distinguishing harmful from benign readings is an ongoing debate in the technical working groups Usman sits on. "I do not recall a single meeting which passed without debating this issue."

Distillate fuels generally show higher quality

Distillate fuels showed fewer contamination incidents than residual grades, but flash point non-compliance remains a concern.

Flash point – the lowest temperature at which fuel vapour can ignite – has a minimum of 60°C under SOLAS, the international convention governing ship safety. Several samples tested during the period returned results below that threshold.

Cold flow properties also attracted attention, particularly for vessels trading in northern hemisphere winters. "If you have fuel in your storage tank with a high cold filter plugging point [CFPP], and without heating, then that fuel can cause real problems in your filters if the operating temperature is below the CFPP of the fuel," Usman explains.

Biofuels add new complexity

Biofuel uptake continued to grow, with no significant incidents reported. Biofuel development is moving quickly, however. Fuels produced from novel bio-feedstocks are entering operational trials, and complex-grade biofuels are under active discussion.

"All these new types of biofuels should be considered separately," Usman says. "One feedstock can be different to the other feedstock, and they can behave differently under different blending conditions."

Supply, management, and procurement

Fuel quality issues can originate at different points in the supply chain. In major bunkering hubs such as Houston, for example, cross-contamination in the bunker fuels has been linked to shared pipeline infrastructure. However, responsibility does not end with the supplier. "As a fuel buyer, you also have the responsibility for how you manage the fuel onboard, because sometimes it's a lack of best fuel management practices which may cause the problem," says Usman.

A recurring issue is the gap between procurement decisions made ashore and the operational realities faced by engineers at sea. The fuel ordered may not match the vessel's requirements or handling capabilities.

“A clear line of communication needs to be established between the technical department and fuel procurement team, and onto charters to convey any ship's fuel handling limitations – compare what's on offer with specific requirements at a port to make an informed decision about acceptability of bunkers,” Usman says.

Missing elements

There are still aspects of fuel quality that remain difficult to detect or fully understand. Marine residual fuels are complex mixtures. Even when unusual compounds are detected, it is not always clear whether they are harmful or at what concentration they become a problem.

This uncertainty is one of the reasons the industry is looking to performance-based laboratory methods that assess or attempt to simulate how a fuel might behave in the real world. Developing such methods, however, is not straightforward. “Test method development is a resource-intensive process…it requires years and years and effort,” Usman says.

CIMAC is progressing work on performance-based laboratory methods. In collaboration with an international research lab, they hope to establish meaningful benchmarks linking fuel characteristics to operational performance.

No room for complacency

The high compliance rates in the second half of 2025 are encouraging. However, as Usman notes, fuel quality incidents arrive without warning, and even a small number of severe cases can have real consequences for the vessels, crews and assets involved.

“This is a reminder that fuel quality cannot be treated as a box‑ticking exercise. Even with high overall compliance, the increase in severe and clustered incidents shows how quickly marginal issues can escalate into operational and safety risks.”

“As fuels become more complex, driven by new blending practices, alternative feedstocks and tighter regulation, the need for technical discipline, robust testing and clear communication across the supply chain becomes even more critical,” Usman adds. “Bunker fuel today behaves differently than it did a decade ago, and our approach to managing it must evolve accordingly.”

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Main image: Top-down view of a bunker barge moored alongside a large merchant vessel. Credit: Shutterstock.

Inline image: Dr Muhammad Usman. Credit: Lloyd’s Register