FuelEU well-to-wake GHG intensity: formula, factors, example

FuelEU Maritime does not regulate how much fuel a ship burns. It regulates how much greenhouse gas each unit of energy used on board carries across its whole life — from extraction and production (well-to-tank) to combustion in the engine (tank-to-wake). That figure, the well-to-wake (WtW) GHG intensity in grams of CO₂-equivalent per megajoule, is what a ship's yearly energy use is scored against under the Article 4(2) reduction trajectory Reg (EU) 2023/1805 · Art. 4 ↗. Get the intensity of each fuel right and the compliance balance, the pooling position and the penalty all follow from it; get it wrong and every downstream number is wrong by the same factor.

This page walks through how the intensity is built: the fuel properties Annex II defines, the Annex I formula that combines them, a worked example for heavy fuel oil that is recomputed every time this site is built, and the full table of Annex II default values.

What Annex II defines

For each fuel pathway, Annex II of the Regulation publishes the raw components Reg (EU) 2023/1805 · Annex II ↗ — not a finished intensity. Four kinds of value matter:

• Lower calorific value (LCV) — the energy released per gram of fuel, in MJ/g. It converts a bunkered mass into the energy the intensity is expressed against, and it is the denominator of the tank-to-wake term.
• Well-to-tank intensity (WtT) — the upstream emissions of producing and delivering the fuel, already expressed in gCO₂e/MJ. For fossil fuels this is a fixed default; for biofuels and renewable fuels of non-biological origin it comes from the fuel's certified pathway.
• Emission conversion factors (Cf) — grams of CO₂, CH₄ and N₂O emitted per gram of fuel combusted. The CO₂ factor dominates; the CH₄ and N₂O factors are small but are multiplied by large warming potentials.
• Methane slip (Cslip) — the share of fuel that leaves the engine uncombusted. It is zero for oil fuels and engine-class specific for LNG, which is why Annex II lists LNG once per engine class (Otto medium-speed, Otto slow-speed, diesel slow-speed and lean-burn spark-ignition).

The formula

Annex I combines the components in two steps Reg (EU) 2023/1805 · Annex I ↗. First the tank-to-wake intensity: the combusted share of the fuel, weighted by each gas's 100-year global warming potential and divided by the calorific value, plus a separate term for the slipped methane, which counts in full as CH₄.

TtW = (1 − C_slip) × Cf_CO₂·GWP_CO₂ + Cf_CH₄·GWP_CH₄ + Cf_N₂O·GWP_N₂OLCV + C_slip · GWP_CH₄LCV

Cf_x

emission conversion factor of the fuel for gas x [g gas / g fuel]

GWP_x

100-year global warming potential (AR4: CO₂ 1, CH₄ 25, N₂O 298)

C_slip

non-combusted fuel fraction (methane slip; engine-class specific for LNG)

LCV

lower calorific value of the fuel [MJ/g]

The well-to-wake intensity is then the sum of the upstream and on-board terms:

WtW = WtT + TtW

WtT

well-to-tank intensity of the fuel pathway (Annex II) [gCO₂e/MJ]

TtW

tank-to-wake intensity (formula above) [gCO₂e/MJ]

The attained intensity of a ship over a reporting period is the energy-weighted average of the WtW intensities of the fuels it used. The formula is the same for every fuel; only the Annex II inputs change.

Worked example: heavy fuel oil

Worked example

Well-to-wake intensity of HFO

✓ Engine-verifiedregulator-printed example · recomputed automatically · updated 2026-08-28

A ship burns conventional heavy fuel oil (ISO 8217 grades RME–RMK). Annex II gives the raw components; the well-to-wake GHG intensity follows from the Annex I formula under AR4 GWP values (CH₄ 25, N₂O 298).

Lower calorific value (LCV)

0.0405 MJ/g

Well-to-tank intensity (WtT)

13.5 gCO₂e/MJ

Cf CO₂

3.114 g CO₂ / g fuel

Cf CH₄

0.00005 g CH₄ / g fuel

Cf N₂O

0.00018 g N₂O / g fuel

Methane slip (Cslip)

0 —

1. 1
   GWP-weighted emissions per gram of fuel3.114×1 + 0.00005×25 + 0.00018×298 = 3.16889 gCO₂e/g
2. 2
   Tank-to-wake intensity (÷ LCV; no slip term for HFO)3.16889 / 0.0405 = 78.24420 gCO₂e/MJ
3. 3
   Well-to-wake intensity13.5 + 78.24420 = 91.74420 gCO₂e/MJ

Result · WtW GHG intensity of HFO91.74420 gCO₂e/MJ

2025 limit 89.33680 · exceeded by 2.40740

The result is the Commission's published well-to-wake default for conventional heavy fuel oil. It is not typed into this page: the inputs shown above are resolved from Carbonlogy's coefficient package, run through the same calculation the product uses, and compared with the published digits every time this site is built. If the coefficients, the calculation or the displayed digits ever disagree, the build fails and this page does not ship.

Annex II default factors

The full set of Annex II components, exactly as Carbonlogy stores and computes with them. The footer carries the instrument and the date from which the values apply.

Pathway	Fuel	Engine class	LCV (MJ/g)	WtT (gCO₂e/MJ)	Cf CO₂	Cslip
HFO	HFO	—	0.0405	13.5	3.114	0
LFO	VLSFO	—	0.0410	13.2	3.151	0
MDO_MGO	MGO	—	0.0427	14.4	3.206	0
LNG_OTTO_MEDIUM	LNG	OTTO_MEDIUM_SPEED	0.0491	18.5	2.750	0.031
LNG_OTTO_SLOW	LNG	OTTO_SLOW_SPEED	0.0491	18.5	2.750	0.017
LNG_DIESEL_SLOW	LNG	DIESEL_SLOW_SPEED	0.0491	18.5	2.750	0.002
LNG_LBSI	LNG	LBSI	0.0491	18.5	2.750	0.026
LPG_PROPANE	LPG	—	0.0460	7.8	3.000	0
LPG_BUTANE	LPG	—	0.0460	7.8	3.030	0
METHANOL_FOSSIL	METHANOL	—	0.0199	31.3	1.375	0
H2_NG_ICE	HYDROGEN	—	0.1200	132.0	0	0
NH3_NG_ICE	AMMONIA	—	0.0180	121.0	0	0

Three reading notes:

• LNG is engine-specific. The slip fraction, and therefore the intensity, depends on the engine class declared for the ship. A ship burning LNG with no declared engine class cannot be assigned an intensity, and Carbonlogy reports that gap rather than guessing a row.
• Uncertified alternative fuels default to fossil. Methanol, hydrogen and ammonia without a certified sustainable pathway are assessed at the least-favourable fossil pathway for that fuel type — the rows shown here. A certified pathway replaces those defaults with the fuel's own well-to-tank figure.
• Grades map to rows. Annex II groups marine fuels by ISO 8217 grade: the residual grades RME–RMK share the HFO row, the RMA–RMD grades the LFO row, and the DMX–DMB distillates the MDO/MGO row. The bunker delivery note names the grade; the row follows from it.

Last reviewed 27 August 2026 · Carbonlogy Compliance Team

From intensity to the target

Intensity becomes compliance by comparison with the Article 4(2) trajectory Reg (EU) 2023/1805 · Art. 4 ↗: a reference value derived from the 2020 fleet average, reduced by a growing percentage at each milestone year. Each reduction applies from 1 January of its milestone year and holds until the next milestone.

Year	Reduction (%)	Target (gCO₂e/MJ)
2025	2	89.33680
2030	6	85.69040
2035	14.5	77.94180
2040	31	62.90040
2045	62	34.64080
2050	80	18.23200

A ship whose energy-weighted attained intensity sits below the year's target carries a compliance surplus; above it, a deficit to be settled by pooling, banking or the remedial penalty — each covered in its own article.

How Carbonlogy applies it