Very low sulphur fuel oil is not one product. It is a family of blends that meet the same sulphur limit by different routes, and the differences between them are the buyer's problem.

When the global cap on marine fuel sulphur fell to 0.50%, the market did not simply switch to a lower-sulphur version of the same fuel. Refiners and blenders met the limit using whatever streams were available to them — and those streams differ by region, by refinery configuration and by season. The result is a grade defined by a ceiling rather than by a recipe.

For a buyer, this changes the nature of the specification. With the old high-sulphur grade, the relevant questions were largely commercial. With VLSFO, stability and compatibility became technical questions with operational consequences, and they are not fully answered by a certificate showing the sulphur limit is met.

Stability, compatibility and cold flow

Stability describes whether the asphaltenes in a fuel stay in suspension. An unstable blend drops sediment in tanks and lines, and the consequence is filter blockage and separator problems rather than an argument about a certificate. Total sediment after ageing, tested to the method the contract names, is the property that speaks to this — and it is the one most often omitted from an abbreviated spec sheet.

Compatibility is a different question, and it concerns two fuels rather than one. Two blends that are individually stable can precipitate sediment when mixed, which is why commingling parcels from different sources in the same tank is a real operational risk. The practical answer is segregation, and a compatibility test before any deliberate mixing.

Cold-flow behaviour caught many buyers out early. Some compliant blends carry a much higher pour point than the residual fuel they replaced, and a fuel that pours at the load port may not pour in a colder trading area without heating. Pour point belongs in the purchase specification with the destination climate in mind, not as an afterthought.

Catalyst fines — aluminium and silicon carried over from refinery processing — remain the classic wear risk. The limit is set in the fuel standard, but the delivered figure matters less than what reaches the engine, which depends on the vessel's own treatment plant.

• Total sediment after ageing specified, with its test method.
• Pour point matched to the intended trading area.
• Aluminium and silicon limits stated explicitly.
• Segregated stowage where parcels come from different sources.
• Compatibility tested before any deliberate commingling.
• Representative sample retained at the point of delivery.

Buying it sensibly

Buy against a full specification rather than a sulphur figure. The standard for marine residual fuels covers the properties that matter; naming it, with the specific grade and any tightened limits, gives you something enforceable. A contract that says only "VLSFO max 0.50% S" has specified one property out of a dozen.

Keep supply consistent where you can. A buyer taking the same blend from the same source repeatedly has a far smaller compatibility problem than one buying opportunistically across several regions, and the saving on a cheap stem rarely covers a debunkering.

Retain samples at delivery, sealed and witnessed. Fuel quality claims are decided on the delivered sample; without one, a claim is an opinion. This is the same discipline that governs every other petroleum cargo, and the sulphur cap has made it more important, not less.

About the author

Regi Atlantic Trading Desk

Regi Atlantic Energy Limited

Notes from the people who source, trade, store and ship the cargo — written to answer the questions counterparties actually ask us before a contract goes firm.