CII Fuel Mix Correction

Quantify how a multi-fuel bunker mix (LNG, methanol, ammonia, biofuel blends, drop-in replacements) changes the attained CII relative to a baseline single-fuel reference. The principal tool for evaluating CII benefit of fuel switching, biofuel pilot purchases and dual-fuel operation under MEPC.336(76).

CIIFuel mixMEPC.336(76)MEPC.364(79) Cf

Ship and voyage inputs

Ship typeShip capacityDWTDeadweight: used for bulk, gas, tanker, container, general cargo, refrigerated, combination and LNG carriers (MEPC.353(78) Table 1).Distance travelled in reporting yearnmTotal nautical miles travelled in the reporting year, from IMO DCS data.Reporting year

Baseline (single-fuel reference)

Total bunker burn assumed as if 100% of energy came from this single fuel. Conventionally VLSFO for post-2020 ships, HFO for legacy vessels.

Baseline fuelTotal bunker mass (energy-equivalent)tonnesThe mass of the baseline fuel that would deliver the same total energy as the actual mixed bunker.

Actual fuel mix

One row per fuel actually burned. The calculator preserves total energy: if the actual mix has a different LCV than the baseline, mass-equivalence per energy is enforced via the energy split percentages.

FuelEnergy share%

Energy shares sum to 100.0%. Should equal 100%.

Baseline attained CII: 2.373g CO₂/(cap·nm)

Very Low Sulfur Fuel Oil (VLSFO, ≤0.50% S) only.

Corrected attained CII (actual mix): 2.192g CO₂/(cap·nm)

1750 t Very Low Sulfur Fuel Oil (VLSFO, ≤0.50% S), 633 t LNG - Otto cycle, medium-speed (4-stroke dual-fuel)

CII reduction from fuel mix: 7.6%

0.181 g CO₂/(cap·nm) absolute

Required CII (reference): 3.792g CO₂/(cap·nm)

2025 required CII per MEPC.353(78) and MEPC.338(76).

Baseline rating: A

Major superior performance. No corrective action required.

Corrected rating: A

Major superior performance. No corrective action required.

Changing the inputs requires JavaScript. The calculator above shows its default inputs and result. The formula, symbols, and regulatory sources are shown in the Formula section below.

Formula, assumptions, and limits

\text{CII}_\text{baseline} = \frac{F_\text{base} \cdot C_{f,\text{base}} \cdot 10^6}{\text{Capacity} \cdot D}

Symbol	Meaning	Unit
$\text{CII}_\text{baseline}$	Attained CII if 100% baseline fuel were burned	g CO₂/(cap·nm)
$\text{CII}_\text{actual}$	Attained CII for the actual mix	g CO₂/(cap·nm)
$F_\text{base}$	Mass of baseline fuel (energy-equivalent)	t
$F_j$	Mass of fuel $j$ in the actual mix	t
$C_{f,\text{base}}$ , $C_{f,j}$	Tank-to-wake CO₂ conversion factor	t CO₂/t fuel
$\text{LCV}_\text{base}$ , $\text{LCV}_j$	Lower calorific value	MJ/kg
$E_\text{total}$	Total bunker energy	MJ
$s_j$	Energy share of fuel $j$ in the mix	fraction
$Capacity$	DWT (cargo) or GT (ro-pax / cruise)	t or -
$D$	Distance travelled in the reporting year	nm

Source: IMO Resolution [MEPC.336(76)](https://www.imo.org) - 2021 Guidelines on operational CII; IMO Resolution [MEPC.337(76)](https://www.imo.org) - Reference lines; IMO Resolution [MEPC.338(76)](https://www.imo.org) - Reduction factors; IMO Resolution [MEPC.339(76)](https://www.imo.org) - Rating boundaries; IMO Resolution [MEPC.364(79)](https://www.imo.org) - Cf factors

In short

Quantify how a multi-fuel bunker mix changes attained CII relative to a single-fuel baseline. Covers LNG, methanol, ammonia, biofuel blends and dual-fuel operation under MEPC.336(76) and MEPC.364(79).

Learn the theory BIMCO CII and Emissions Clauses