LNG bunkering is the delivery of liquefied natural gas to a ship as fuel, at around minus 162 degrees Celsius. The transfer itself is a cryogenic operation with its own standard and its own delivery note. The commercial case behind it changed on 1 January 2026.
What makes it different from a conventional stem
The three delivery modes are the same as for oil, but almost nothing else is.
- Ship to ship, from a purpose built LNG bunker vessel
- Truck to ship, for smaller volumes, typically ferries and coastal tonnage
- Shore to ship, from a terminal pipeline, which is how most large scale LNG bunkering happens
The operation adds steps that have no equivalent in oil bunkering:
- Inerting and gas freeing of the transfer line before and after
- Cool down, bringing the line and tank gradually to cryogenic temperature so thermal shock does not damage equipment
- Emergency shutdown linkage between both parties, tested before transfer begins
- Vapour return, so boil off gas displaced from the receiving tank goes back rather than to atmosphere
The governing standard is ISO 20519, which covers the liquid and vapour transfer hardware, the operational procedures, the training and qualification of the people involved, and the requirement for the supplier to issue an LNG bunker delivery note.
LNG has its own delivery note, and it carries more than quantity
An oil bunker delivery note answers what grade, how much, what sulphur. An LNG delivery note has to answer something harder, because the emissions performance of the fuel depends on its composition and on what happens to it in the engine.
The MARPOL Annex VI delivery note requirements were written for oil. For LNG the practical evidence set is wider: composition, calorific value, quantity delivered by energy rather than by mass alone, and the conditions of transfer.
Methane slip is the thing that decides whether LNG pays
A fraction of the methane passes through a dual fuel engine unburned and reaches the atmosphere. That is methane slip, and methane is a far more potent greenhouse gas than CO₂ over the short term, which is why it has become the central question for LNG as a marine fuel (VPS).
How much slips depends heavily on the engine:
| Engine type | Typical methane slip |
|---|---|
| Medium speed four stroke Otto cycle | The highest of the common configurations |
| Low pressure dual fuel, first generation two stroke | Around 2.0 to 2.5 g/kWh |
| Low pressure dual fuel, current generation | Around 1.0 to 1.2 g/kWh |
| High pressure diesel cycle | Lowest, because combustion does not rely on a premixed charge |
This is why two ships burning the same LNG from the same bunker vessel can have materially different compliance outcomes. The fuel is identical. The engine is not.
On 1 January 2026 methane started costing money
Until the end of 2025, EU ETS covered CO₂ only. From 1 January 2026 it also covers methane and nitrous oxide (reporting on the change). For an LNG fuelled ship trading to Europe, slip stopped being an environmental talking point and became a line in the allowance calculation.
FuelEU Maritime already counted it, because it measures greenhouse gas intensity well to wake, which includes slip. LNG typically lands in the region of 76 to 85 gCO₂eq/MJ depending on engine and upstream pathway, against the 2025 limit of 89.3368, so it generally produces a compliance surplus rather than a deficit.
So LNG still helps under both regimes. What changed is that the size of the benefit now depends on a number you have to be able to evidence.
The gap between a default value and a measured one
This is the part worth reading twice. Where a ship does not measure its own methane slip, a default factor applies. Gasum, an LNG supplier has published an analysis putting the default for medium speed Otto engines at 3.1%, against measured values closer to 1% on well performing installations. On their figures, a large container ship reporting measured slip instead of the default could avoid more than a million euros a year in EU ETS costs.
That figure comes from an LNG supplier and should be read as an argument from an interested party, not as a neutral benchmark. The direction of it, though, is not controversial: defaults are conservative by design, and a conservative default applied to a large ship over a year is expensive.
The saving is not in burning less gas. It is in being able to prove what your engine actually did with it.
Which is exactly where the evidence problem shows up
To claim a measured slip figure rather than a default, you need a chain that holds together under verification: what was delivered and its composition, what the engine did with it, and who attests to each part. That chain crosses at least three parties, and today each of them keeps their own copy.
The delivery is where the chain starts. VesselChain records each delivery once, at the point of delivery, signed by the accredited verifier the regulation already requires, and held identically by every party that depends on it. What that means if you operate the vessel is here.
LNG also sits inside the wider MARPOL Annex VI framework, where the same consumption data feeds the annual reporting obligation and the carbon intensity rating.
Frequently asked questions
What is LNG bunkering?
LNG bunkering is the delivery of liquefied natural gas to a ship for use as fuel, at approximately minus 162 degrees Celsius. It can be done ship to ship from an LNG bunker vessel, truck to ship, or shore to ship from a terminal.
Which standard applies to LNG bunkering?
ISO 20519 specifies the bunkering of LNG fuelled vessels. It covers the liquid and vapour transfer systems, operational procedures, training and qualification of personnel, and requires the supplier to issue an LNG bunker delivery note.
What is methane slip?
Methane slip is the fraction of methane that passes through a dual fuel engine unburned and reaches the atmosphere. It varies considerably by engine type, and it counts against a ship under well to wake accounting.
Does LNG still make sense under EU rules?
Generally yes. LNG typically achieves a well to wake intensity around 76 to 85 gCO₂eq/MJ against a 2025 FuelEU limit of 89.3368, producing a compliance surplus. The size of the benefit depends on the methane slip figure you can evidence.
Does EU ETS cover methane?
Yes, from 1 January 2026. Before that the maritime scope covered carbon dioxide only. Methane and nitrous oxide were added, which directly affects LNG fuelled ships.
Why does measured methane slip matter?
Where a ship does not measure its slip, a conservative default factor applies. Reporting a measured figure instead can materially reduce the emissions attributed to the ship, but only if the measurement and the underlying fuel data survive verification.
Is LNG bunkering available everywhere?
No. Availability is concentrated in northern Europe, parts of the Mediterranean, Singapore and a number of North American and Asian hubs, and it is expanding. Bunkering LNG requires planning around infrastructure in a way that oil does not.
