CII - Ship



What is CII?

The Carbon Intensity Indicator (CII) is an IMO regulation that aims to gradually reduce carbon emissions from ships, lowering the marine industry’s overall environmental footprint. This mandatory measure falls under Annex VI of the International Convention for the Prevention of Pollution from Ships (MARPOL), and targets emissions from vessel operations.

What is attained CII? What is required CII?

Attained CII is the actual carbon intensity indicator value calculated from annual data reported by ship owners per each individual vessel. The required CII is the carbon intensity indicator value set by the IMO regulations for each individual vessel annually

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How is CII calculated?

Attained CII is calculated as the ratio of the total mass of CO2 emitted by a ship to the total transport work it undertakes in a calendar year. Total transport work numbers are determined using data from the IMO Data Collection System (IMO DCS) to calculate a vessel’s Annual Efficiency Ratio (AER) or capacity gross ton distance (cgDIST). AER and cgDIST include different information as ship’s capacity:

  • AER: Ship’s total annual fuel consumption, nautical miles traveled and deadweight tonnage (DWT)
  • cgDIST: Ship’s total annual fuel consumption, nautical miles traveled, and gross tonnage (GT)

Different ship types will use DWT or GT as their capacity:

  • DWT is used for bulk carriers, tankers, container ships, gas carriers, LNG carriers, general cargo ships, refrigerated cargo carrier and combination carriers
  • GT is used for cruise passenger ships, ro-ro cargo ships (vehicle carriers), ro-ro cargo ships and ro-ro passenger ships

A ship’s attained CII is then compared with the required CII. Based on this difference, vessels receive a carbon intensity rating describing their performance.

Sebastien Crouzet

International Statutory Affairs Manager

Bureau Veritas M&O

Unlike IMO’s other environmental regulations, the CII is a moving target, regularly lowering emissions up through 2030. This is why shipowners need to prepare now, building a firm foundation for ongoing operational improvements with the support and verification of classification societies.

What is a CII rating?

Ships receive one of five carbon intensity ratings from A to E, with A indicating the highest performance level and E indicating the lowest performance level. Targeted annual performance ratings must be assessed, improved if necessary and recorded in Part III of a vessel’s Ship Energy Efficiency Management Plan (SEEMP). Ships receiving a D for three consecutive years or E rating will need to submit a Corrective Action Plan for reaching the required annual operational CII. The midpoint of the C rating value corresponds to the required annual operational CII.

Bureau Veritas services for CII compliance

To demonstrate CII compliance, ship owners will need to calculate their attained CII and develop a verified SEEMP Part III. As a recognized organization with delegation from flag administrations, Bureau Veritas can support shipowners throughout the CII verification process. And when delegated by flag administrations, our experts can verify SEEMP, corrective action plans and CII.

In addition, fleet owners and managers can use our VeriSTAR Green application to easily calculate attained CII and simulate ship performance rating. They can also reach technical advisory services to improve performance from independent experts from BV Solutions M&O.

Bureau Veritas is always by our clients’ side, helping ship owners and operators prepare for changing environmental regulations. To learn more about the CII, EEXI and SEEMP alternative fuels and carbon emissions reduction, marine actors can read our technical reports and white papers.


  • Which vessels require a CII?

    CII is required for every ship of 5,000 GT and above covered by one or more of the categories in the regulations listed below and to which MARPOL Annex VI chapter 4 is applicable.

    MARPOL Annex VI Regulation

    Ship type


    Bulk carrier


    Combination carrier




    Cruise passenger ship


    Gas carrier


    General cargo ship


    LNG carrier


    Refrigerated cargo carrier


    Ro-ro cargo ship


    Ro-ro cargo ship (vehicle carrier)


    Ro-ro passenger ship



  • How do I implement SEEMP Part III?

    Implementing a SEEMP Part III includes steps of assessment and monitoring onboard energy consumption. You can find out more here.

  • What is the timeline for CII compliance?

    On January 1, 2023, shipowners will need to have completed and verified SEEMP Part III, which concerns CII requirements. Throughout 2023, ships must be operated in compliance with Parts I, II and III of their SEEMP, and have their data collected under the IMO DCS.

    Between January and March 2024, shipowners will need to calculate attained CII from 2023 and report it to the relevant administration. Reported data and attained CII calculations will be verified through May 2024, enabling ships to receive a carbon intensity rating. Vessels achieving a performance rating of C or higher will be issued a statement of compliance for fuel oil consumption reporting and operational carbon intensity rating valid until the next year.

    Ships with three consecutive D or one E rating will need to develop a corrective action plan in their SEEMP. This is to be verified by the administration or authorized organization before a statement of compliance is issued.

    Cii Timeline

    Download our infographic

  • How are IMO DCS, SEEMP, and CII related?

    The IMO DCS is the data reporting system that collects fuel consumption and emissions data from ships. Ships are required to develop a SEEMP, which monitors energy efficiency and helps improve ship performance. CII is calculated using data from the IMO DCS, and plans for limiting carbon intensity are developed in SEEMP Part III.

    To comply with IMO regulations, vessels will need to update their SEEMP to account for CII requirements. CII improvement plans are mandatory, and SEEMP Part III will be subject to periodical verifications and audits, for which guidelines are being developed.

  • Is CII tank-to-wake or well-to-wake?

    The CII takes a tank-to-wake approach to emissions, accounting for CO2 emitted from ship fueling to fuel consumption. This framing notably does not consider the upstream emissions that occur during fuel production (an approach known as “well-to-wake”).

    For some ships, this short-term focus on limiting downstream emissions may encourage a shift from traditional to low-carbon fuels. In the long-term, however, a well-to-wake approach might be taken into account in regulations.

  • What happens if I do not achieve a C or higher CII rating?

    Ships with a low CII rating must propose a suitable plan to realistically obtain a C rating. A corrective action plan must be developed either:

    • For ships rated D for three consecutive years
    • For ships rated E for one year

    If a vessel receives an inferior rating for data collected in calendar year YYYY, this plan will need to be amended to contain corrective actions. These actions should map how it will achieve the required annual operational CII for data collected in the calendar year YYYY+2.

Find out more about CII