Carbon Intensity IndicatorCII
An IMO operational measure of how much CO₂ a ship emits per unit of transport work, graded A–E each year.
The Carbon Intensity Indicator (CII) is the IMO’s operational efficiency metric: it measures grams of CO₂ emitted per deadweight-tonne-mile (or capacity-mile) over a calendar year and assigns each applicable ship an annual rating from A (best) to E (worst).
Required reduction factors tighten the thresholds each year, so a ship rated A or B today can slip without efficiency action. A D rating for three consecutive years, or an E in any year, requires a corrective action plan. CII applies to ships of 5,000 GT and above and is set under IMO MEPC resolutions.
On TheMaritime
Also known as: CII, carbon intensity indicator, CII rating.
Related terms
Energy Efficiency Existing Ship IndexEEXI
A one-time IMO design-efficiency standard that existing ships must meet, the in-service counterpart of the EEDI for new ships.
International Maritime OrganizationIMO
The United Nations agency that sets global rules for ship safety, security and pollution prevention.
Slow Steaming
Deliberately sailing below design speed to cut fuel consumption, emissions and effective fleet supply.
Very Low Sulphur Fuel OilVLSFO
Marine fuel with no more than 0.50% sulphur, the compliant fuel for most waters under the IMO 2020 sulphur cap.
Plain-English reference definition — our own explanation of a standard shipping concept, not a licensed source or legal advice. See the full glossary or the broader maritime dictionary.
Last reviewed: June 2026.