Bunker fuel testing and marine surveying business Maritec-Naias on Friday (12 June) issued an alert regarding high levels of catalytic fines and elevated acid numbers present in multiple VLSFO bunker samples from deliveries in the Singapore port: 

During the period of 20 May 2026 and 02 June 2026, Maritec Pte. Ltd. (hereafter referred to as Maritec-Naias) conducted testing on five samples representing Very Low Sulphur Fuel Oil (VLSFO) deliveries from two suppliers in the Singapore port. The analyses revealed Aluminium and Silicon (Al+Si) concentrations ranging from 61 mg/kg to 68 mg/kg.

It is important to note; these values exceed the ISO 8217:2010/2017 specification limit of 60 ppm but remain within the permissible tolerance limit of 72 ppm under ISO 4259 for a single test result. In this regard, Catalytic Fines content, (Aluminium+Silicon), above 60 ppm is regarded as high. Of the five samples, three originated from one supplier, while the remaining two were from another.

Aluminium and Silicon constitute the principal classes of abrasive solids in fuels. Elevated concentrations of such particles at the engine inlet can precipitate abnormal wear and tear of fuel system components, piston rings, and cylinder liners. To safeguard against this, many engine manufacturers stipulate a maximum threshold of 15 mg/kg Al+Si at the engine inlet.

The primary method of mitigating Catfines is through an efficiently operating fuel purification system. Monitoring Aluminium and Silicon levels both before and after centrifugation provides a reliable measure of the system’s effectiveness in removing these contaminants.

During a similar period, Maritec-Naias also tested fifteen bunker fuel samples representing VLSFO that exhibited elevated Acid Numbers, ranging from 2.0 mg KOH/g to 2.5 mg KOH/g. While these values remain within specification limits, they are nonetheless considered at higher side. Elevated Acid Numbers may stem from contamination with acidic compounds such as Phenolic compounds and Alkyl Resorcinols, often associated with Estonian Shale Oil. Such contaminants can lead to operational complications including sludge formation, fuel pump seizures, and compromised injection equipment cleanliness.

Maritec-Naias Recommendations

• High Catfines monitoring: Maritec-Naias advises collecting samples at critical points within the fuel system — including the fuel oil tank transfer pump, before and after centrifuge, service tank, and after fine-filter — to evaluate the efficiency of fuel cleaning.
• Elevated Acid Numbers: For fuels with elevated Acid Numbers, Maritec-Naias recommends conducting Gas Chromatography-Mass Spectrometry (GC-MS) using the Solid Phase Extraction (SPE) method to identify the specific acidic compounds present or upgrading your marine fuel testing package to MFTP Plus, which enables pre-emptive monitoring to detect major harmful substances prevalent in the market, such as Cashew Nut Shell Liquid (CNSL), Phenolic compounds and Alkyl Resorcinols that cause damage to equipment.

Maritec-Naias states, while all data and findings presented in this document are true, it does not reflect on the overall quality of fuel being supplied in Singapore region. If you intend to bunker at this region, please request for a Certificate of Quality (CoQ) prior to loading.

Photo credit: Hans Reniers on Unsplash
Published: 15 June, 2026

Lloyd’s Register Fuel Oil Bunkering Analysis and Advisory Service (FOBAS) on Thursday (7 May) released a bulletin stating that tests on several fuels from Singapore identified a chemical fingerprint consistent with Estonian shale oil, while vessels using these fuels reported operational issues:

In recent weeks FOBAS has tested a number of fuels from Singapore that under detailed chemical analysis with GCMS methods, showed a chemical fingerprint consistent with Estonian shale Oil. 

Shale oil and particularly Estonian shale oil is seen from time to time in fuel blends in certain ports, particularly in Singapore and ARA region. In some of these recent fuels, the estimated concentrations are high, potentially up to 25% of the blend. 

The routine analysis results of these fuels appear on-spec compared to ISO8217 RMG380 grade fuels including Total Sediment results not particularly high.

The vessels using these fuels recently tested with confirmed shale oil are reporting certain operational issues, including excessive sludging throughout the fuel system, blocking of filters and in one case fuel pump issues.

As detailed chemical analysis is not carried out routinely on all fuels, it is difficult to say how many fuels may also have shale oil in the blend. However, from looking at other fuels properties and other supplies from the same barges and suppliers, we can estimate many other vessels have bunkered fuels with varying levels of Shale oil. Not all these ships have yet given operational feedback.

In general, shale oil is often seen as mentioned in certain ports and in many cases, fuels used without problem. However, there is also a long history of fuel stability and sludge related problems related to Estonian shale oil so while it seems not every shale oil blended fuel necessarily will cause a problem there certainly seems an increased risk and in particular in fuels with very high levels of shale oil.

We would suggest requesting from a supplier if shale oil has been used in the fuel blend when bunkering. Also paying particular attention to the Total Sediment results and fuel performance particularly though the purifier. We would also suggest fuels are put into use as soon as possible to quickly identify any potential issues and avoid long term storage.

Photo credit: Hans Reniers on Unsplash
Published: 8 May, 2026

Marine insurer Skuld on Monday (27 April) wrote an advisory after it has seen several vessels receiving bunkered fuel, mostly from Southeast Asia, that meets ISO 8217 specifications but reveals significant contamination with unusual chemical compounds under advanced testing: 

Recently, Skuld has seen several vessels reporting bunkered fuel that is on specification as per ISO 8217 parameters. Still when advanced tests were carried out, Gas Chromatography MassSpectrometry (GCMS) showed a high presence of hydrocarbon compounds, phenolic compounds, and other alkylresorcinol derivatives.

Most of these bunkered fuels stem from Southeast Asia, particularly in Singapore, Hong Kong and Malaysia. The results mentioned above are similar to those reported by fuel testing laboratories, i.e., that it include levels of shale oil components. Some bunker suppliers may intentionally supply blended, low-quality marine fuels amid sharply rising bunker prices due to the war in the Middle East.

Some of the GCMS reports we saw, which contained hydrocarbon compounds like dihydro-dicyclopentadiene and indene, had a concentration level between 5,000 ppm – 14,000 ppm, and Alkylresorsinol concentration between 4,700 ppm – 6,000 ppm. We have previously seen very high concentrations of such compounds, which are commonly associated with Estonian shale oil, and in 2019, we saw a number of VLSFO fuels from the ARA region containing such compounds.

Whilst shale oil is not considered a contaminant and is an acceptable blend component under the ISO 8217 standard, at high concentrations it can cause operational challenges onboard as the presence of hydrocarbon compounds, phenolic oxygenated compounds, and other alkylresorcinol derivatives is not typical of marine fuels.

There is a risk that these compounds may result in sludge formation, filter and purifier fouling, and fuel injection system issues, and that poor engine performance may be experienced, but this is not certain, and in general, most vessels using fuels with these unusual compounds do not experience problems. A risk assessment should be performed, and the GCMS report must be taken as a warning.

When GCMS is performed as part of a troubleshooting exercise in which the vessel has reported problems, we can link the problems and the detected chemical compounds. In case the fuel is not free from material that renders the fuel unacceptable for use in marine applications because the fuel contains any added substance or chemical waste that jeopardises the safety of the ship, adversely affects the performance of the machinery or is harmful to personnel or contributes overall to additional air pollution, then the fuel does not meet the requirements of clause 5 of ISO 8217.

Skuld advises its members and assureds to always perform due diligence when ordering or procuring bunkers and follow precautionary measures when handling this kind of fuels.

• It is very important always to conduct a vetting procedure when selecting a good bunker supplier. Clarification should be sought from their supplier regarding the blended component used.
• A fuel analysis should always be carried out before using the bunkered fuel. As these phenolic compounds cannot be detected in the standard ISO 8217 test, an extended advanced GCMS test from a reputable fuel laboratory is recommended.
• Perform correct fuel handling and enhanced monitoring of the fuel treatment machinery onboard, such as purifiers and filters.
• Good record keeping should be carried out, such as tank sounding records, fuel transfer and consumption, correct temperature settings in the fuel tanks, purifiers and main and auxiliary engines.
• Fuel System Check is recommended to check the fuel quality of the fuel entering the engine.

Photo credit: Hans Reniers on Unsplash
Published: 28 April, 2026