VLSFO, HSFO or MGO: how to choose the right marine fuel

The choice between VLSFO, HSFO and MGO is set first by sulphur rules and the ship's equipment, then by trading pattern and cost. This guide sets out the rules, the practical risks of each fuel and the questions to ask before ordering.

The rules that frame the choice

Since 1 January 2020, MARPOL Annex VI has limited the sulphur content of fuel oil used outside emission control areas to 0.50% m/m, down from 3.50%. From 1 March 2020 a carriage ban also applies: a ship without an approved exhaust gas cleaning system may not carry fuel above 0.50% sulphur for its own use.

Inside the designated sulphur emission control areas, the limit has been 0.10% m/m since 1 January 2015. The 0.10% limit has applied in the Mediterranean ECA since 1 May 2025; it will apply in the Canadian Arctic and Norwegian Sea ECAs from 1 March 2027 and in the North-East Atlantic ECA from 1 September 2028.

A ship fitted with an exhaust gas cleaning system, or scrubber, approved as an equivalent under regulation 4 of the Annex may use fuel above these limits, provided the system meets the required emission performance.

The three main options

HSFO: residual fuel above 0.50% sulphur. Only usable by ships with an approved scrubber. In ISO 8217:2024 these fuels have their own specification table.
VLSFO: residual or blended fuel at or below 0.50% sulphur. It is the default choice for most ships without scrubbers outside ECAs. Composition varies widely because it is blended from different components.
MGO and MDO: distillate fuels. Low-sulphur MGO at 0.10% or below is the usual choice for ECA operation in ships without scrubbers.

Residual fuels at or below 0.10% sulphur, often called ULSFO, are covered by ISO 8217 and available in some ports. They can be an alternative to MGO in ECAs where the engine and fuel system are suitable, but availability is limited.

Matching fuel to the trading pattern

Start with the route, not the price. Map how many hours the ship spends inside ECAs, how long it sits at berth in EU ports, and where it can realistically bunker.

A ship trading mostly outside ECAs, without a scrubber, will burn VLSFO for most of its time and carry enough MGO for ECA passages and EU port stays.
A ship trading largely inside ECAs, such as a short-sea vessel in northern Europe, may run almost entirely on MGO or 0.10% fuel.
A scrubber-fitted ship can burn HSFO in most areas, but still needs compliant fuel for times the scrubber is unavailable and for places where local rules restrict wash-water discharge.
Tank arrangement matters: each fuel needs segregated storage, settling and service capacity, which limits how many grades a ship can carry.

Scrubbers: the price spread is not the whole story

The commercial case for a scrubber rests on the price difference between HSFO and compliant fuel, which moves with the market. When comparing, include the system's power demand and maintenance, the time the ship trades in areas where open-loop discharge is restricted, and the need to switch to compliant fuel if the system fails.

Under IMO guidance (MEPC.1/Circ.883), if a scrubber cannot be returned to compliant operation within one hour of a malfunction, the ship should change over to compliant fuel. That means carrying enough VLSFO or MGO as a reserve, which is a real cost even when it is rarely burnt.

Compatibility and stability

Because VLSFO is blended, two deliveries of nominally the same grade can behave very differently. Mixing a more paraffinic fuel with a more aromatic one can cause asphaltenes to drop out as sludge, which blocks filters and overloads purifiers.

Load new fuel into empty tanks wherever possible and avoid mixing deliveries from different suppliers.
If mixing cannot be avoided, ask the laboratory for a compatibility test on samples of both fuels before co-mingling.
Check stability results on the test report. For residual fuels at or below 0.50% sulphur, ISO 8217:2024 adds reporting of total sediment existent and accelerated, while total sediment potential remains the specification limit.
Store and heat fuel as the laboratory and engine maker recommend, and avoid leaving small amounts in tanks for long periods.

Operating on distillates

MGO is clean and stable, but its low viscosity brings its own risks. Engine makers set a minimum viscosity at the engine inlet, and fuel pumps and injection equipment can wear or lose efficiency if the fuel is too thin or too hot. Ships that run on MGO for long periods may need fuel coolers or chillers, and crew should follow the engine maker's guidance on temperature change rates during changeover.

The changeover itself must follow the ship's written procedure under MARPOL Annex VI, with the ship fully on compliant fuel before it enters an ECA, and the volumes, times and positions recorded.

Cost trade-offs beyond the price per tonne

Energy content: distillates and residual fuels deliver different amounts of energy per tonne, so compare cost per unit of energy, not just per tonne.
Cylinder oil: fuel sulphur drives the choice of cylinder oil base number. Ships switching between fuels need the right oils on board.
Handling: residual fuels need heating, settling and purification; poor-quality VLSFO can raise sludge disposal and maintenance costs.
Emissions costs: the EU monitoring rules set default CO2 factors of 3.114 tonnes per tonne for heavy fuel oil (RME to RMK), 3.151 for light fuel oil (RMA to RMD) and 3.206 for gas oil (DMX to DMB), which feed directly into EU ETS costs.
Availability: a cheaper grade is only cheaper if it can be bunkered at a port on the route, in the quantity and quality needed.

Questions to answer before ordering

Which sulphur limits apply on each leg, including ECAs, EU berths and national rules?
Is the scrubber, if fitted, approved and fully operational, and are there discharge restrictions on the route?
Which tanks will be empty to receive the new fuel?
Which ISO 8217 edition and grade will be specified?
Is the cylinder oil on board suitable for the fuel to be burnt?
Is a reserve of compliant fuel needed for changeovers or scrubber failure?

Atlas Bunkering helps owners and managers compare offers for each grade across trusted suppliers, and recommends independent surveying and accredited laboratory testing on every stem, arranged on request.

Questions and answers

Can I mix VLSFO from two different suppliers?

It is best avoided. VLSFOs are blended from different components and may be incompatible. If mixing is unavoidable, have a laboratory run a compatibility test on samples of both fuels first.

Does a scrubber-fitted ship need to carry compliant fuel?

In practice, yes. If the scrubber fails and cannot be restored within one hour, IMO guidance expects the ship to change over to compliant fuel, and some ports restrict wash-water discharge.

Is MGO always required in an ECA?

No. The requirement is fuel at or below 0.10% sulphur, or an approved scrubber. MGO is the most common choice, but 0.10% residual fuels can also be used where available and suitable for the engine.

Sources

This guide is general information, not legal or technical advice. Check the current rules and your engine maker's guidance for your vessel.