What is the CII Rating? — MARPOL Annex VI Carbon Intensity Indicator A-E Guide

Q: Can I improve my CII by adding a scrubber?

No scrubbers reduce SOx, not CO2. CII improvement comes from fuel efficiency (slow steaming, route optimisation, hull cleaning, retrofits) or low-carbon fuels (LNG, biofuels, methanol).

Q: Does CII apply to offshore support vessels?

Currently no OSVs are excluded from the CII regime. This may change under Phase 2. See our OSV compliance hub.

Definition: What is the CII?

The Carbon Intensity Indicator (CII) is a ship’s measured annual operational carbon intensity, calculated as the ratio of CO2 emissions to transport work. It applies to ships of 5,000 GT and above trading internationally, under MARPOL Annex VI Regulation 28. The attained CII is compared against a required CII line, producing a rating from A (superior) through E (inferior).

How CII is calculated

In essence:

Attained CII = annual CO2 emissions (g) ÷ (deadweight tonnage × nautical miles sailed)
Calculation uses IMO DCS (Data Collection System) data that ships already submit.
The required CII is the 2019 reference value reduced by an annual CII reduction factor.
Rating bands A-E are defined by fixed ratios of attained to required CII (dd vectors), published by IMO per ship type.

The reduction factor through 2030

2023: −5%
2024: −7%
2025: −9%
2026: −11%
2027–2030: to be set by the MEPC 84 Phase 2 review, expected to tighten considerably.

A ship rated D or E: what happens?

A rating of D for three consecutive years or E for one year triggers a mandatory corrective action plan in the ship’s SEEMP Part III, approved by the flag state or Recognised Organisation. The ship must identify the causes and specify operational or technical measures to improve the rating.

What CII does not do

CII is operational — it measures carbon intensity in operation, not design. It does not price emissions (that is EU ETS and the forthcoming IMO Net-Zero Framework). A poor CII rating does not currently carry a financial penalty under IMO, but:

Charterers increasingly use CII clauses in time charters.
Banks and insurers reference CII in sustainability-linked financing.
Port authorities may offer differentiated port fees based on CII.

Interaction with FuelEU Maritime and the Net-Zero Framework

FuelEU Maritime is Well-to-Wake intensity (g CO2-eq/MJ). CII is Tank-to-Wake intensity (g CO2/transport work). Both apply simultaneously.
The IMO Net-Zero Framework is expected to introduce a Well-to-Wake GFI alongside or replacing CII. See What is the IMO Net-Zero Framework?

Shipowner action in 2026

Run a scenario analysis using DCS data to project 2026–2030 ratings.
If any ship is at D or E risk, prepare SEEMP Part III corrective action in advance.
Pair CII forecasting with FuelEU Well-to-Wake data to prioritise decarbonisation investments.
Watch MEPC 84 outcomes — see our MEPC 84 guide.

Ready to operationalise this?

Run a 3-minute readiness scorecard or book a 30-minute call with our compliance specialists to map this to your fleet.

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Frequently Asked Questions

Is a CII rating of D or E a detainable deficiency?

No. A poor CII rating is not itself a Port State Control detainable deficiency. However, the corrective action plan in SEEMP Part III is mandatory and its absence can be flagged.

Do passenger ships use the same CII formula as cargo ships?

Passenger ships and cruise ships use a different transport-work denominator (gross tonnage miles) and have their own reference lines.

Can I improve my CII by adding a scrubber?

No — scrubbers reduce SOx, not CO2. CII improvement comes from fuel efficiency (slow steaming, route optimisation, hull cleaning, retrofits) or low-carbon fuels (LNG, biofuels, methanol).

When will the 2027-2030 CII reduction factors be set?

MEPC 84 initiates Phase 2 of the review. A decision is expected at MEPC 85 in October 2026, with application from 2027.

Does CII apply to offshore support vessels?

Currently no — OSVs are excluded from the CII regime. This may change under Phase 2. See our OSV compliance hub.

What is the CII Rating? — Carbon Intensity Indicator Explained