Key Specifications
Main engine fuel for the vast majority of deep-sea commercial vessels without exhaust gas cleaning systems
Technical Detail
What changed in 2020
Prior to IMO 2020, most deep-sea vessels burned HFO/IFO 380 with sulphur content up to 3.50%. The IMO cap cut this to 0.50% globally, forcing either a fuel switch (to VLSFO or MGO), installation of scrubbers to remove sulphur from exhaust, or a move to alternative fuels. VLSFO emerged as the commercial solution for most vessels.
Blend variability
VLSFO is not a single product but a family of blends. Refiners and blenders combine residual streams with lighter cutter stocks to hit the 0.50% sulphur target. This means VLSFO supplied at different ports can have materially different viscosity, density, compatibility, and stability characteristics. Careful pre-bunker testing and compatibility checks with existing onboard stocks are important.
Stability and compatibility issues
Because VLSFO blends can contain asphaltenes in variable proportions, co-mingling fuels from different sources can cause asphaltene precipitation — sludge formation in tanks, filters, and separators. Best practice is to segregate stems from different sources or run compatibility tests before mixing.
Cold flow and cat fines
Some VLSFO blends have elevated pour points that can cause handling issues in cold climates without adequate heating. Cat fines (aluminium and silicon residues from refinery catalytic cracking) can be elevated in some blends and require careful separator management to avoid engine wear.
Where to Bunker VLSFO
Ports in our directory where VLSFO is available as a standard commercial grade:
Frequently Asked Questions
Can I mix VLSFO from different ports?
Risky without testing. Blends vary; asphaltene incompatibility can cause tank sludging. Best practice: segregate tanks until you've run a compatibility test, or order from the same supplier across voyages where possible.
What happens if my VLSFO is off-spec?
Under ISO 8217, specific parameters (sulphur, viscosity, density, flash point, water, sediment, cat fines, CCAI) define compliance. Off-spec fuel is typically handled via commercial dispute with the supplier, bunker survey evidence, and independent lab testing.
Is VLSFO cheaper than MGO?
Generally yes, though the spread varies. VLSFO is residual-based and cheaper per tonne than distillate MGO, but total operating cost comparisons should factor in handling, heating, and compatibility risk.
Will VLSFO remain the dominant fuel?
For the near term, yes. Longer-term the transition to biofuels, LNG, methanol, and ammonia will reduce VLSFO's share, but the installed base of conventional engines means VLSFO demand will remain substantial through the 2030s.