Bunker Fuel Quality
VPS: Key steps in avoiding risk of receiving bad bunker fuels
Steve Bee, Dr Malcolm Cooper and Stanley George explain how to safeguard vessel operations against the impact of bad bunkers and share on the key steps that should be taken to avoid the risk of receiving bad bunkers.
Steve Bee, VPS Group Commercial Director, Dr Malcolm Cooper, VPS CEO and Stanley George, VPS Group Science & Technical Manager explained in an article on how to safeguard vessel operations against the impact of bad bunker fuels and shared on the key steps that should be taken to avoid the risk of receiving bad bunkers:
Bad bunkers can significantly impact vessel operations, necessitating intervention from the crew and in some cases result in operational failure – varying from operational damage through to loss of power and subsequently loss of propulsion. Mitigating the impact of bad bunkers can help to prevent damage to vessel’s equipment and protect the safety of those on board and the environment. Bad bunkers can lead to fuel stability problems, chemical contamination and poor cold-flow properties. This paper describes the key steps that should be taken to avoid the risk of receiving bad bunkers.
Bad Bunkers
Bad bunkers refer to fuel of substandard quality, which can lead to operational disruptions and challenges in fuel management. Common fuel quality concerns include poor stability, chemical contamination, corrosive tendencies, poor combustion and poor cold flow characteristics. Thorough testing of bunkered fuel prior to putting it in operation is highly advantageous as it reveals potential issues inherent in the fuel. This data often enables proactive measures to mitigate the risk of operational complications stemming from such fuel.
Whilst the general quality of bunker fuel has been consistent over recent years, it is important to note that off-specification fuel statistics are typically based on the criteria outlined in Table 1 and 2 of ISO 8217 standard. There have been numerous occasions when bunker fuel meeting these criteria has proven to be unsuitable for onboard use due to its poor quality and on a number of occasions has caused catastrophic failures (e.g. ARA contamination case – August 2022 and March 2024, Houston contamination case April 2023 and Singapore contamination case August 2022). This necessitates additional testing methodologies such as GCMS, WAT/WDT, and Reserve Stability Number to accurately assess fuel quality.
The increase in reported operational issues stemming from contaminated fuels, which often elude detection through routine ISO 8217 testing, has experienced a notable uptick in recent years. This trend can be attributed, at least in part, to the drive towards decarbonization, notably spurred by initiatives such as IMO 2020. Consequently, fuel suppliers are increasingly experimenting with a diverse range of feedstocks to serve as blend components in conventional fossil fuels.
As the world’s largest marine fuel quality testing company covering 50% of all fuel testing, VPS can offer valuable insights and advice in relation to poor quality and/or contaminated fuel. Proactive, pre-burn, fuel testing on a regular basis, is definitely a highly recommended approach to mitigating risks to vessel operations, crew safety and environmental impact. The typical off-specification parameters associated with engine failure are usually Pour Point, Total Sediment Potential, Cat-fines and/or Water content. Whilst the International Marine Fuel Quality standard, ISO8217, includes these test parameters, it’s certainly a more diligent and wiser approach, to consider a fuel’s overall stability, cold-flow properties, chemical contamination and potential corrosivity.
At VPS, we possess the proficiency and extensive experience necessary to conduct specialised tests specifically designed to detect these issues. Our tailored testing protocols enable us to identify potential fuel-related challenges and offer operational guidance to minimise associated risks effectively.
Fuel Stability
Both High Sulphur Fuel Oils (HSFOs) and Very Low Sulphur Fuel Oils (VLSFOs), can suffer with varying degrees of instability due to thermal-aging and over-heating, high sediment content, or chemical contamination, to name but a few potential causes. Instability usually manifests itself through sediment formation, which can in turn, block onboard filters, pipework, potentially then starving an engine of fuel.
ISO8217 includes the Total Sediment Potential (TSP) test, which is a good indicator of the amount of sediment which may be potentially produced in relation to a fuel’s stability. However, additional tests such as Total Sediment Accelerated (TSA), a deliberate fuel-aging test, Total Sediment Existent (TSE), a measure of fuel cleanliness and the determination of a fuel’s stability reserve, via Separability Testing, to measure the fuel’s capacity to hold long chain asphaltenes within the fuel solution, can provide much more information regarding fuel stability determinations.
In particular, Separability Number is an excellent accompaniment to the routine hot filtration methods. It can identify potentially troublesome unstable fuels even when the Hot Filtration Test methods indicate a low sediment content. Conversely, it may indicate that a high sediment fuel is in fact quite stable and unlikely to form sludge. This information in combination, is extremely useful from an operational perspective, as it will indicate in advance if and what mitigation steps are appropriate.
Chemical Contamination
Over the years chemical contamination of marine fuels has resulted in many onboard operational issues, with numerous chemicals and chemical groups being identified as the cause. Major widespread contamination events, include Houston (2018), with over 200 vessels damaged due to a potential phenolic contamination, to Singapore (2022) where 80 vessels were affected by chlorinated hydrocarbons within the fuel and then more recently ARA (2023) where around 20 vessels suffered issues due to a cocktail of styrenes and dienes within the fuel. In between such times, many smaller cases of chemical contamination have been identified by VPS. Thankfully, many at a pre-burn stage, thus avoiding any operational issues or damage cases.
Over time, all of the following chemicals have been found by VPS in marine fuels. The effects of these are highlighted below:
Risks from chemical contamination of fuel can be significantly mitigated through pre-burn screening of fuels using VPS Chemical Screening Service. This low-cost test, utilising Gas Chromatography Mass Spectrometry (GCMS) analysis, will warn of the presence of over 70% of all volatile chemicals within fuel. With both VLSFO and HSFO we continued to see cases of vessel damages due to chemical contamination during 2023. Focusing specifically on the VPS GCMS-Head Space Chemical Screening service, as a damage prevention service, 19.9% of applicable marine fuel samples received by VPS since 2018, have undertaken this rapid, pre-burn protection service, with an average 8% of samples tested, giving rise to a “Caution” result, indicating the presence of at least one chemical contaminant and thus the notified vessel has avoided any damages.
In April 2023, a Singaporean-owned chemical and product tanker bunkered 415 m/tons of VLSFO in Houston. The vessel began to burn the fuel in May and quickly began to experience numerous issues with the auxiliary and main engines, such as exhaust gas deviating temperatures and the wearing of fuel pumps and plunger barrels. In addition, problems such as start-failure due to insufficient fuel injection, pressure build up, as well as worn out and leaking fuel pumps.
Of greater concern was the complete engine stoppage enroute to the next US port, when the main engine failed. Multiple attempts were made to start the engine, all without success.
Subsequent VPS forensic laboratory testing, utilising a proprietary Gas Chromatography Mass Spectrometry (GCMS) Acid Extraction methodology, detected the presence of several phenols and fatty acid compounds within the fuel.
The vessel initiated the necessary repairs to both auxiliary and main engine fuel pumps, at a total spares cost of $200,000. In hindsight the vessel owner stated pre-burn screening would have helped significantly in avoiding such damages and costs.
Cold-Flow Properties
The cold-flow properties of fuels are also important to monitor closely, especially when sailing in colder temperature regions. The Pour Point of HSFOs, VLSFOs and MGO fuels, should always be monitored when colder climates are encountered. Pour Point was the most common MGO off-specification parameter in 2023, with 36.6% of MGO off-specs attributed to Pour Point. However, prior to reaching the pout point of MGO fuel, its cloud point and cold-filter plugging point behaviour offer earlier warning-signs of potential cold-flow issues, relating to wax precipitation from the fuel. It is key fuel management practice to measure these two cold-flow parameters within MGO distillates.
VLSFO fuels have a higher paraffinic content than HSFO and as a consequence, have a greater potential to precipitate wax, which can cause filter and pipework blockages, which can ultimately starve an engine of fuel. As VLSFOs are dark fuels, the cloud point cannot be seen, as it can with a distillate fuel. Therefore in 2019, VPS developed a proprietary test method to measure the Wax Appearance (WAT) and Wax Disappearance Temperatures (WDT) of VLSFOs.
Generally, it is recommended that the fuel temperature is kept approximately 10oC above the PP to avoid risk of solidification. However, in the majority of the global bunker ports in 2022-23 the average WAT was often higher than 30oC, and WDT higher than 40oC. This may also mean heating the fuel to avoid solidification during transfer. However, this should not necessarily mean an increase in storage temperature. Fuel oil transfer pumps on board are generally positive displacement pumps and can handle certain amount of wax that are present in the fuel.
If the fuel has a high WAT/WDT, VPS recommend heating the fuel just before the transfer operation.
Therefore, additional fuel tests, such as, Total Sediment Existent (TSE), Separability Number (Reserve Stability Number, RSN), Wax Appearance/Wax Disappearance Temperature Testing, Cloud Point, Cold Filter Plugging Point and Chemical Screening, can provide significantly greater and more valuable protective information, when assessing fuel quality than ISO8217 alone. This is why VPS offer our Additional Protection Service (APS) “bundles”. The APS includes the standard ISO8217 parameters but also fuel-relevant additional tests, in order to support our customers to greater levels with respect to, asset, crew and environmental protection.
Over the years, VPS Off-specification fuel data has proactively highlighted the potential risks associated with certain parameters. The importance of regular and wider-ranging marine fuel testing, through the Additional Protection Service, will definitely support mitigation strategies to prevent disruptions in vessel power supply due to fuel-related issues. Even a minor fuel quality issue can prove costly. A 2018 report by the Swedish Club highlighted the average cost per incident of fuel-related damage on vessels is $344K.
Photo credit: VPS
Published: 9 April 2024
Bunker Fuel Quality
VPS: High bunker prices meet declining fuel quality
Of the current 29 Bunker Alerts issued by VPS from January to July 2026, the combination of abrasive issues due to elevated cat-fines, plus fuel stability issues, account for 72% of these alerts.
Steve Bee, Group Marketing and Strategic Projects Director of marine fuels testing company VPS, on Monday (24 August) reviewed 2026 marine fossil fuel quality to date and the high number of issues being witnessed:
Marine fuel buyers entered 2026 facing a perfect storm, suffering some of the highest bunker prices ever experienced, paired with a sharp and concerning decline in fuel quality. Across the traditional marine fossil fuel supply chain, VPS has seen a marked rise in fuel quality issues, with the Middle East conflict playing a major role in driving both price volatility and quality deterioration. For ship owners/operators, the message is clear, today’s fuel market is not only more expensive, it is also becoming more complex and unpredictable, with a higher degree of operational risk.
This deterioration is already showing itself in the test data VPS have produced. Between January and July 2026, VPS issued 29 Bunker Alerts, more than the total issued across the whole of 2024 and already closing in on the 37 alerts recorded throughout all of 2025. In just seven months of 2026, the scale and frequency of these alerts underline a clear, accelerating rise in fuel quality problems across the industry. Of the current 29 Bunker Alerts issued so far, Jan-Jul 2026, the combination of abrasive issues due to elevated cat-fines, plus fuel stability issues, account for 72% of these alerts. The ports requiring cat-fines and/or stability-related bunker alerts were, ARA, Balboa, Busan, Callao, Hamburg, Houston, Las Palmas, Philadelphia, Piraeus, Rotterdam, San Roque, Singapore and Valencia.
What is of additional interest is that marine gas oil does not account for a single Bunker Alert so far in 2026. It is HSFO and VLSFO dominating the fuels requiring such warnings.
Looking at the rate of off-specifications across each of the main marine fossil fuel types, HSFO is currently running at 8.87% of samples tested, being off-specification for at least one ISO8217 test parameter, whilst VLSFO has 9.88% off-specification level, MGO has 9.03% and ULSFOs is at 19.58%. ISO 8217 provides specification requirements for marine fuel as delivered to the ship. From a commercial perspective the fuel is only required to meet the specification at the point of custody transfer, ie at the ship’s manifold. However, compliance at this point, is not a guarantee of assurance that the fuel can be used without operational difficulties throughout its onboard lifecycle. This includes, how the fuel is stored, treat and consumed in main engines, generator engines, boilers, or other machinery. The condition of the fuel which ultimately reaches the machinery, is also strongly influenced by onboard fuel management, including storage and settling temperatures, settling time, purification temperature and throughput, purifier configuration and desludging arrangements, filtration, maintenance of the correct injection viscosity and other operational factors.
This is why knowing the characteristics of the bunkered fuel is critical to managing it correctly onboard. Appropriate testing can identify characteristics which, although not necessarily resulting in an ISO 8217 specification failure, may warrant additional operational attention. VPS therefore evaluates bunker fuels not only against the applicable specification requirements, but also provides operational advice where analytical findings indicate that additional precautions may be appropriate during storage, treatment or consumption.
VPS testing and observations, based on over 45 years of marine fuel testing experience and expertise, strongly align with a recent Linkedin post by marine and energy consultants, Brookes Bell. Their post highlighted a growing concern within the industry, stating a P&I Club had reported that bunker-related claims are up 50% this year, with many of the fuels involved having technically passed ISO8217 standard specification testing.
The same post noted that some ISO8217-compliant fuels have still caused operational damage. This has left shipowners to manage complex evidentiary disputes after problems arose. Its key warning was clear: Standard compliance testing alone isn’t catching the problem. If “passing spec” is not necessarily the same as being “safe-to-burn”, then the critical question becomes, “What additional testing is needed to identify the real operational risks?”
VPS have recognised that for some time, the ISO8217 standard is not an all-encompassing set of tests providing the highest level of asset, crew and environmental protection. For this reason, VPS offer a range of additional tests, as well as our Additional Protection Service (APS) test bundles. For example in the case of avoiding damages from cat-fines, the Fuel System Check (FSC) service, can provide valuable information in regard to monitoring purifier efficiency and the removal of cat-fines, protecting the engine to a higher degree. Whereas, Separability Number testing, is a key compliment to the hot filtration stability tests of TSP, TSA and TSE in mitigating stability risks. Should additional cold-flow information be required, the VPS proprietary Wax Appearance Temperature (WAT) testing provides key storage and fuel transfer temperature information. Whilst the VPS chemical screening services can identify potentially harmful chemicals within a fuel before the fuel is burnt. Then more detailed Gas Chromatography Mass Spectrometry (GCMS) forensic analysis provides key information to potentially support the fuel claims process.
VPS account managers and technical specialists can help shipowners and operators determine which laboratory tests are most appropriate for their fleet, based on the fuel characteristics, vessel operations and potential risk exposure. This guidance can support the mitigation of risks linked to engine damage, SOLAS compliance, legislative requirements and wider operational reliability.
The VPS Technical Advisory Team reviews bunker analysis results together with the vessel operational observations to provide practical advice on fuel storage, handling, purification and overall fuel management. Where appropriate, additional laboratory tests, or test bundles, may be recommended to further evaluate the fuel and assist in identifying the cause of an operational issue, supporting more informed decision-making.
VPS continues to monitor regional and global fuel quality trends through its laboratory network and customer feedback. Information received from vessels experiencing similar operational issues is valuable in helping VPS identify emerging trends and provide timely technical guidance to the wider shipping industry.
Photo credit: VPS
Published: 25 August, 2026
Bunker Alerts
Low flashpoint found in Indonesia bunker fuels, alerts Maritec-Naias
Firm tested eight bunker samples representing LSMDO and B40 fuel grade from vessels that took fuel oil /bunkered in Indonesia ports, which indicated flashpoints as low as 39.5°C.
Bunker Alerts
Maritec-Naias: High levels of Phenolic compounds in China bunker fuels
Firm tested multiple fuel oil bunker samples from vessels that took fuel/bunkered in China ports from 7 June to 28 July, which indicated the presence of high levels of Phenolic compounds.
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