Why GLEC and FuelEU disagree on LNG by 30%

Two well-respected methodologies, one fuel, one molecule, two answers that differ by 30%. If that surprised you, you are in good company — it surprised us too the first time we sat the two side by side. This note explains where the gap comes from and which one Provenship uses when.

The two numbers

• FuelEU Annex II well-to-wake factor for LNG: 3.748 t CO2eq per tonne LNG.
• GLEC Framework v3.0 well-to-wake factor for LNG: 2.870 t CO2eq per tonne LNG.
• Gap: roughly 30% — the FuelEU value is higher.

The reason: methane slip

Both methodologies agree on the upstream emissions (extraction, liquefaction, transport, regasification). They diverge on engine-out methane. A small fraction of LNG passes through the combustion chamber unburned and is emitted as methane — methane slip. Methane has a 100-year global-warming potential of about 28 (and a 20-year GWP near 80), so even small unburned fractions matter.

FuelEU Annex II prescribes engine-class-specific slip percentages: a four-stroke dual-fuel medium-speed engine can run 2–3% slip, a two-stroke low-pressure system can sit around 1.5%, a two-stroke high-pressure (Otto-cycle exception) can drop to 0.2%. The Annex II default — what Provenship defaults to — bakes in the population-weighted slip for the EU-flagged fleet.

GLEC v3.0 takes a different stance. It amortises slip over a global fleet-average engine mix and produces a single representative number. For an operator running an Otto-cycle low-slip engine, GLEC is closer to truth; for an operator on legacy medium-speed dual-fuel, GLEC under-counts. The Annex II number is — in expectation — closer to the regulated fleet's real footprint.

Which one Provenship uses, and when

FuelEU compliance is regulatory. The operator's filing must use the Annex II factor (or a documented engine-specific override). Provenship uses 3.748 for the FuelEU calculation, full stop.

Shipper-side carbon accounting (CDP, SBTi, ISO 14083) is a different audience. Some shippers explicitly accept GLEC. Where Provenship emits a shipper-facing carbon statement, the methodology used is labelled inline — the operator knows which factor they are looking at and why it differs from the regulatory filing.

Why this matters for honesty

A platform that prints one LNG number without labelling the methodology gives the operator a false sense of precision. Both 3.748 and 2.870 are right under their respective frames; only the labelling reveals which question is being answered. Provenship labels.