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Infineum: Spin test shows promise of identifying stable VLSFOs and bunker fuels

Infineum has been evaluating various test methods to support the industry with a view to finding a new test method to better indicate the suitability of VLSFOs.

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The stability issues being reported regarding the use of very low sulphur marine fuels are often related to the fuels’ shelf life, which makes it increasingly important to assess fuel quality over extended periods. Rob Ashton, Infineum Marine Fuel Additive Business Development Manager, explains how selecting the most appropriate combination of tests to evaluate stability and compatibility over time is increasingly important in order to offer the most complete protection for ship operators:

Since the introduction of the IMO 2020 sulphur cuts, the stability of very low sulphur fuel oils (VLSFO) at point of sale has largely been on specification. However, uncertainty around the shelf life of these fuels, which can be less than three months, means this remains one of the key areas of concern for VLSFO use. This has led Infineum to invest in the assessment of the various tests that are available to help operators to ensure the fuel they have on board is suitable for use.

In a previous Insight article Sediment concerns in marine fuels, we evaluated the Separability Number test (ASTM D7061), which measures the Reserve Stability Number and is being widely used to assess fuel oil stability and compatibility. Following a thorough study of this test we concluded that it is unsuitable for determining stability and compatibility of VLSFO over the fuels’ shelf life. While we understand the rationale for employing this test, in our view, the Separability Number test methodology eliminates the natural solvency of the fuel from the equation by saturating the fuel medium with polar aromatic solvent (toluene) at between 1:3 and 1:20 ratio. This means that the test analyses some characteristics of the asphaltene species contained within the fuel, but does not assess the stability of the fuel itself, which is the most critical factor for the new VLSFOs.

This is owing to the fact that most additives targeting asphaltene management show benefits in the Separability Number test at very low treat rates. There are some commercial additives that can trigger large improvement responses in this test but are unable to demonstrate any robust level of performance in other key test methodologies (e.g. Potential Total Sediment (TSP) and S ASTM D7157 value), even at elevated treat rates. It is questionable whether the low treat rates offered for the Separability Number test are giving any tangible benefit in ensuring VLSFOs are suitable for use on board ship.

Spin test evaluation

Infineum has been evaluating various test methods to support the industry with a view to finding a new test method, which would better indicate the suitability of VLSFOs. Among the tests that have been evaluated is the Spin Test, which has been developed by Alfa Laval, a leading provider of fuel oil purifier equipment for the marine industry.

Other Spin Test methods, used for determining sediments and water and fuel oils are also available (e.g. ASTM D1796). However, these test methods generally require fuel dilution, which, once again, can impact the effect of the fuel’s natural solvency on results. One of the key attractions of the Alfa Laval test methodology is that fuel is unadulterated and is only subject to the forces likely to be experienced in ships’ purifier systems. Stokes law* is the underlying principle here.

The Alfa Laval test is carried out by heating the fuel to a defined temperature, dictated by the required viscosity of the fuel, spinning in a heated centrifuge at a fixed rpm for a fixed time period (read more). Once the test is complete, the centrifuge tubes are removed from the centrifuge and inverted so that the fuel oil drains out leaving the compacted sediment in the base of the tube. The fuel oil operability is evaluated by determining the quantity of sediment that has come out of solution from the fuel sample and settled within the centrifuge tube. The rating system is shown below:

vlfso table

Using the Spin Test to assess operability

A severe VLSFO was selected for testing, which was off-specification for Total Sediments Potential at 0.14 mass %, versus the maximum specifications in ISO 8217 of 0.1 mass %. The Spin Test yielded a value of 1.5% sludge volume. For this particular case, the result aligns with TSP, meaning that this fuel could cause onboard issues in the purifier system and its use should be avoided.

To assess the ability of the test to discriminate the effects of additive use, a sample of the fuel was treated with Infineum asphaltene management technology. A second sample was treated with another commercially available additive at the same treat rate, which was significantly above the supplier’s recommended treat rate.

On visual inspection, the Infineum technology delivered a clear benefit, demonstrating how effective the additive is at dispersing the asphaltenes. The Spin Test result of 0.1% sludge volume confirmed these initial observations. TSP was also carried out and a reduction from 0.14 mass % to 0.01 mass % was recorded, confirming that the fuel additised with Infineum technology would be suitable for use on board.

The competitor additive offered no TSP improvement and was unable to move the fuel into a safe operating window according to the Spin Test. This result reinforces the importance of verifying additive performance in a suitable test to ensure that an actual real-world operability benefit is bestowed by the additive in the fuel oil.

vlsfo spin results 1 1

Linking performance to ship trial

A study was also undertaken to relate Spin Test performance back to a ship trial that had been carried out on a Suez Max tanker with a two-stroke engine – see case study. To recap, the fuel supplier had produced on-spec VLSFO (<0.1 mass % total sediment), which deteriorated rapidly on board ship to the point where the fuel was unusable (>0.23 mass % TSP) and had to be de-bunkered. An identical VLSFO blend was made with Infineum additive technology to give a TSP <0.04 mass %.

Samples of the components used to make the ship trial fuel had been retained and although they were 18 months older (and hence more severe in nature), it was decided to evaluate this test case in an extended Spin Test programme. Initially, TSP and Separability Number (RSN) testing were carried out over an eight-week period to assess the fuel’s performance.

At the start of the test, the VLSFO without additive was borderline off spec at 0.11 mass %, vs. <0.10 mass % in the original ship trial, but it rapidly deteriorated to 0.19 mass % after the four-week period. This level was maintained over the eight-week test period, compared with the deterioration in TSP to 0.23 mass % during use in the original ship trial blend. By comparison, the Separability Number test yielded a high stability reserve (RSN <<1) indicating that it would remain suitable for use over the whole test period, which it clearly did not.

may 21 vlsfo 1

When the VLSFO was treated with Infineum technology, it greatly improved the TSP at the start of the test down to a level of 0.04 mass % which mirrored the original ship trial result.

may 21 vlsfo 2

After four weeks, the treated VLSFO drifted off spec for TSP (0.13 mass %) albeit to a lower level than observed in the unadditised samples. It then maintained that slightly off-spec level over the eight-week period, whereas in the original field trial TSP was maintained at 0.04 mass % throughout the 15-week ship trial. Again, Separability Number returned a high stability reserve (RSN <<1) despite the fuel being off spec for TSP.  

The TSP/RSN protocol above was repeated with the Spin Test, this time over a 10-week period.

vlsfo spin shelf life 1

According to Spin Test data, the base fuel was deemed unfit for use at the start of the test (0.8% sediment) with further deterioration over the 10-week time period to 1.4% sediment. This is aligned with the TSP results.

Infineum additive technology maintained the fuel below the unfit for purpose level according to the sludge level in the Spin Test (0.3%) over the whole time period despite being borderline off spec for TSP (0.12 mass %) after the 10-week period.

This test programme builds on Infineum’s previous field experience, demonstrating that the Spin Test gives further supporting information, in addition to the Total Sediments test, that enables ship operators to assess the suitability for use of VLSFOs over an extended timeframe. It could be said that the TSP test is a low shear test environment for the fuel, similar to that experienced in storage conditions on board. However, the Spin Test is a higher shear environment (centrifugal force) mimicking purifier operation, which assesses whether sediment will precipitate from a residual fuel while passing through the fuel purifier. Both tests measure different, but relevant, stress factors that fuels experience in storage and purification and consequently offer a more comprehensive picture of how a fuel will perform on board.

Conclusion

There are differences between high sulphur fuel oil and very low sulphur fuel oil from a sediments perspective and, in our view, there is a need for additional tests to ensure the very low sulphur fuels provided into the marine marketplace are suitable for use. The Separability Number test, although historically useful for high sulphur fuel oils, is not able to predict if the new VLSFOs now in the market are suitable for use.

The TSP test, which is the existing reference test in ISO 8217 for assessing sediment, does have issues with repeatability, especially in fuels that have high results or where the performance changes over time. Regardless of this fact, it is crucial that any tests used should provide confidence in operability protection to ship operators. In this regard, the Alfa Laval Spin Test performance translates directly into improved purifier operation for ship operators. Consequently, Infineum believes that a combination of TSP and the Spin Test, coupled with effective asphaltene management additives offer the most complete protection for ship operators.

 

Photo credit and source: Infineum
Published: 7 June, 2021

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Bunker Fuel

Alkagesta highlights key insights on European choke point pressures in August

Update covers dual supply crisis currently shaping global bunker markets — a stalled Strait of Hormuz peace process and Rhine water levels at a 140-year record low — and the implications for Singapore.

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Alkagesta

Malta-based global commodity trading house Alkagesta recently shared latest market insight examining the dual supply crisis gripping global energy markets as diplomatic efforts to reopen the Strait of Hormuz stall and Rhine water levels fall to record lows, creating what the company describes as a “state of emergency” for European inland fuel distribution.

In an article published on Alkagesta Market Insights on 11 August, the company’s trading and market intelligence teams outlined how the convergence of two simultaneous logistical crises is tightening prompt fuel availability across Singapore, Northwest Europe, and the Mediterranean:

Strait of Hormuz transits fell to a near-one-month low of 13 ships on August 9 following an attack on an ADNOC-linked tanker, as both the US and Iran demand war reparations before any reopening agreement can be reached. Simultaneously, Rhine water levels at the Kaub chokepoint fell to 16 cm on August 10 — the lowest since records began in 1880 — with forecasts pointing to a further drop to just 4 cm by August 14, effectively halting barge traffic and trapping fuel oil stocks at the ARA hub.

The supply picture across both key hubs has deteriorated sharply. In Singapore, Middle Eastern fuel oil imports nearly tripled week-over-week to 328,878 mt by July 29 — the highest volume since March — providing some relief as onshore commercial heavy distillate stocks rose to a five-week high of 19.58 million barrels by August 5. However, July bunker fuel sales are estimated to have fallen 3.7% month-over-month to 4.44 million mt, with elevated premiums redirecting prompt demand toward alternative ports including Zhoushan and Port Klang.

In Europe, the VLSFO market remains acutely undersupplied as refiners continue to prioritize high-margin diesel over low-sulfur blending components, while the Rhine crisis has forced barges to operate at just 15–20% of normal capacity — with freight rates from Rotterdam to Karlsruhe rising more than 400% in two months.

Alkagesta’s strategic outlook points to a potential total breakdown in Rhine-linked inland distribution by mid-August, a VLSFO Hi-5 spread likely to remain above $200/mt through Q3, and a global crude market that analysts warn requires an additional 2.1 million b/d for 18 months to rebuild depleted inventories.

Note: The full article can be read here.

 

Photo credit: Alkagesta
Published: 17 August, 2026

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Bunker Fuel

Integr8 Fuels: Why bunker markets could be lower than we thought

Marine fuel prices could prove lower than previously anticipated as easing refinery margins and improving bunker market fundamentals outweigh a still-uncertain crude oil outlook, says Integr8 Fuels.

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By Steve Christy, Expert Contributor, Integr8 Fuels

29 July 2026

We have just seen one false dawn, is there another to come? 

Last month, we wrote about how close we were to the expected lows in Brent and Rotterdam bunker prices, but not yet Singapore. Given what has happened since, a month is not only a long time in politics, but also a very long time in the bunker market. 

There was a resumption of attacks in the Arabian Gulf region on 13 July, followed by targeted Houthi attacks on Saudi Arabia’s Red Sea oil infrastructure and shipping in the Bab el-Mandeb region, the gateway between the Red Sea and the Gulf of Aden. As a result, Brent futures fell to lows of around $70/bbl in late June and early July before surging to a high of $100/bbl on 23 July. Over the same period, Singapore VLSFO fell to $635/mt before climbing to $865/mt, a swing of $230/mt in just 16 days. 

Jul 2026 Graph 01 1024x613 1

Prices at the start of this week fell sharply after a halt in Arabian Gulf attacks over the weekend, with front month Brent was down to intra-day lows of $84/bbl, and Singapore VLSFO $750/mt.  However, at the time of writing there has been a ‘surprise’ attack by Iran, and retaliatory action by the US, with prices rising again.  It looks like we could be at another false dawn. 

The obvious questions are: will there be a return to peace negotiations, and are we close to the end of the war and free-flowing traffic through the strait of Hormuz (and also the Bab el-Mandeb)? The obvious answer is, we don’t know; there are only a few people that are likely to know the answer to this. All we can do is plan for every eventuality. 

Low stocks, higher bunker prices, and a strong Singapore VLSFO premium: it’s a challenge 

For those of us in the bunker market, the point we made last month about Singapore VLSFO trading at a strong premium to crude still holds, albeit slightly less pronounced. The loss of supplies through the Strait of Hormuz, together with the added uncertainty surrounding Saudi product exports from the Jizan and Rabigh refineries on the Red Sea, has sustained this premium. 

These developments are likely to keep the Singapore VLSFO premium to crude at elevated levels until there is greater confidence that Middle East crude and product supplies are returning to more normal trading patterns. Amid all the price volatility, this Singapore VLSFO premium remains a key indicator to watch. 

Backwardation in Brent futures illustrates market psychology 

One month ago, backwardation in Brent futures (front month minus second month) had fallen from $7/bbl to virtually nothing, reflecting the market’s belief that an end to the war was little more than a negotiating step away. It wasn’t. The resumption of attacks, coupled with Houthi involvement in the Red Sea, sent prices sharply higher again, with backwardation in the Brent futures market returning to almost $6/bbl. 

Jul 2026 Graph 02 1024x572 1

The halt in attacks over the past weekend has taken steam out of the market, with prices and backwardation falling sharply. Where we go from here depends if there is again a belief peace is on the horizon, or if this is another false dawn. The past month highlights how impossible it is to predict an ending to the war, and how fragile any expectations of peace can be. 

We cannot ignore the price, but still must look to the future

It is impossible to write a report and not highlight the turmoil of the current market and what is happening. However, we still must look beyond this, to see where we could end up. 

In an earlier report, we suggested the run-up to the US mid-term elections in November may be a backstop to the war. However, even this is not guaranteed. There are many dynamic elements to the economy and voter intentions, but one feature that will always crop up in the US is the gasoline price. This has risen from $3/gallon before the war to over $4/gallon for the past four months. 

Jul 2026 Graph 03 1024x570 1

If it comes to it, will Republican voters want to see a resolution to the war and a return to $3 gasoline prices ahead of the elections? 

We have a change of heart on how low bunker prices can go

We don’t know exact timings, but in any planning, we must look at what happens when the war does finally end and prices fall, whenever that may be. In past reports we have highlighted the view that Brent crude prices are unlikely to fall back to pre-war levels in the $60s, and Singapore VLSFO unlikely to go back in to the $400s. This may be the point at which these views change.

Previous thinking was based on a relatively short war, where there would be a large loss of oil supply and a massive stock-draw. In this case, tighter stock levels would be sufficient to keep prices higher than their pre-war levels once we returned to ‘normality’. This would mean Brent futures in the $70s (and not in the $60s), and Singapore VLSFO in the $500s, and not the $400s.

A number of mainstream analysts also held this view, although there were some that were lower and some higher.

Given the war has already gone on for much longer than almost everyone expected, this thinking must change. Yes, global stocks have been drawn down at a rapid rate, but this is slowing. Higher pricing and inflationary blows have had a major impact on global oil demand, with current indications that total oil demand in the second quarter of this year was some 4 million b/d lower than year earlier levels.

The graph below shows this sharp drop in demand and even if the war comes to an end relatively soon, and demand gets back towards some normality, a structural loss of more than 1 million b/d in global oil demand is still expected to have taken place because of the extended period of conflict.

If the war goes on for even longer, structural losses in global oil demand are likely to be even greater.

Jul 2026 Graph 04 1024x579 1

Source: US EIA

It’s a hard road, but we can get there

This means that once the war does end, market psychology will be looking at a rapid increase in oil supplies going into a global market which is much lower in demand.  This opens the way for prices to easily return to their pre-war levels of Brent in the $60s and Singapore VLSFO in the $400s. 

Now we just need those at the centre of negotiations to get us there.

 

Photo credit and source: Integr8 Fuels
Published: 30 July, 2026

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Bunker Fuel Quality

FOBAS report warns of growing operational risks from ISO-compliant bunker fuels

LR’s latest FOBAS Fuel Quality Report reveals that the biggest fuel quality risks are no longer confined to off-specification fuels, with some compliant fuels creating operational challenges.

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New FOBAS report warns growing operational risks from ISO-compliant bunker fuels

Classification society Lloyd’s Register (LR) on Tuesday (14 July) warned that ship operators are facing a growing risk from fuels that appear compliant under routine ISO 8217 testing but still present operational risks once onboard.

According to LR’s latest Fuel Oil Bunker Analysis and Advisory Service (FOBAS) Fuel Quality Report, covering the first half of 2026, off-specification fuels remain a persistent challenge. 

However, some of the most disruptive cases now involve fuels that pass routine compliance testing but show poor stability or compatibility, or contain non-conventional blend components that are only identified through more detailed investigative analysis.

Several incidents investigated highlighted this trend. In March and April, a number of vessels reported operational difficulties after bunkering fuel in a major bunkering hub. Further forensic analysis found that many of the fuels contained elevated concentrations of Estonian shale oil, in some cases estimated to be around 10-15%.

While 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.

The report also shows that fuel quality variability remains stubbornly high. Off-specification cases remained elevated throughout the first six months of 2026, suggesting that quality issues are no longer isolated events but a more persistent feature of today’s marine fuel supply chain.

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.

At the same time, biofuels (especially FAME blends) are continuing to grow without being a primary source of quality issues. Where issues occurred in blended fuels, they were generally associated with the conventional VLSFO component rather than the FAME fraction.

The report concluded that operators will need to adopt a more proactive approach to fuel management as marine fuels become more diverse and fuel quality risks become harder to identify through routine compliance testing alone.

Greater emphasis on fuel stability, compatibility and understanding fuel composition will be critical to reducing operational disruption and maintaining vessel performance.

Murray Kirkwood, Fuel Specialist Consultant, Lloyd’s Register, said: “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 onboard.

“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 latest findings reinforced FOBAS’ long-standing view that effective fuel management increasingly depends on understanding fuel behaviour rather than relying solely on pass-or-fail specification testing.

By combining routine fuel quality monitoring with forensic investigation of operational incidents, FOBAS provides shipowners with a clearer understanding of emerging fuel quality risks as the industry continues its transition to a more diverse and complex fuel landscape.

Note: The FOBAS Fuel Insight: Fuel Quality Report H1 2026 is available at FOBAS Fuel Insight: Fuel quality reports | LR

 

Photo credit: Lloyd’s Register
Published: 15 July, 2026

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