Marine fuels testing firm VPS Group has detected rising levels of shale oil-derived components in VLSFO bunkered in Singapore, advising ship operators to exercise caution.
According to VPS, testing conducted in February and March 2026 identified around 90,000 mt of VLSFO deliveries containing compounds consistent with Estonian shale oil streams.
While such components are sometimes used in bunker blends, VPS noted they have historically been linked to fuel instability, sludge formation, and filter blockages.
The samples analysed showed elevated concentrations of phenolic compounds, including resorcinol and alkyl benzenediols, ranging between 4,000 ppm and 13,200 ppm. Acid numbers were also higher than typical levels, measured between 1.98 mg KOH/g and 2.34 mg KOH/g, approaching the ISO 8217 limit of 2.5 mg KOH/g.
Despite these findings, VPS said no vessels have reported operational issues so far when using the fuels.
However, the company warned that such fuels may still pose risks over time. These include sludge formation, purifier and filter fouling, and potential impacts on fuel injection system performance, particularly due to storage instability or long-term use.
VPS highlighted that the presence of phenols, fatty acids, and other oxygenated compounds is not typical in conventional marine fuels and may indicate unusual blend components.
The firm advised operators to enhance onboard monitoring, particularly of purifiers, filters, and fuel injection systems, while avoiding co-mingling fuels unless compatibility is confirmed.
It also recommended maintaining detailed operational records, conducting additional sampling before purifiers and at engine inlets, and seeking clarification from suppliers on blend composition and feedstock sources.
VPS said it has contacted vessels that received the affected fuels, all of which confirmed no issues to date, but emphasised that delayed operational impacts cannot be ruled out.
The company added it will continue to monitor the situation and provide updates as further feedback emerges.
