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EEXI vs CII: What’s the Difference and Why It Matters

The maritime industry, responsible for transporting around 90% of global trade, has come under growing pressure to reduce its carbon footprint. To align shipping with the goals of the Paris Agreement, the International Maritime Organization (IMO) introduced a series of measures targeting greenhouse gas (GHG) emissions. Among the most significant are the Energy Efficiency Existing Ship Index (EEXI) and the Carbon Intensity Indicator (CII), both implemented in 2023 under MARPOL Annex VI. Though both aim to improve energy efficiency and reduce emissions, they differ in methodology, scope, and application.
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The Energy Efficiency Existing Ship Index (EEXI) is a design-based technical measure that evaluates the energy efficiency of ships built before 2013. It assesses whether a vessel’s specifications—like engine power and design speed—meet efficiency benchmarks. Ships that fall short of required EEXI levels must undergo technical modifications, such as engine power limitation (EPL), to become compliant.

The Carbon Intensity Indicator (CII), on the other hand, is an operational measure that monitors the actual carbon emissions of ships while in service. It calculates how efficiently a ship transports cargo by assessing annual CO₂ emissions per ton-nautical mile. Ships are rated from A (most efficient) to E (least efficient), with poor ratings requiring corrective action plans.

Key Differences between EEXI and CII

Feature EEXI CII
Definition Design-based index measuring potential CO₂ efficiency of existing ships Operational metric rating annual CO₂ intensity during voyages
What is the purpose Ensure older vessels meet minimum energy efficiency requirements Monitor and improve annual carbon emissions
Which vessel is required to follow Ships ≥400 GT under MARPOL Annex VI Ships ≥5,000 GT under MARPOL Annex VI
Scope One-time compliance at initial survey after Jan 1, 2023 Ongoing, annual reporting and performance evaluation
Focus Ship design and technical characteristics Day-to-day operation and fuel consumption patterns
Formula CO₂ emissions / (capacity × distance) – Based on design specs CO₂ emissions / (cargo transported × distance) – Based on actual data
Timeline Compliance required from first survey post-Jan 2023 Ratings and reporting start from Jan 2023, updated annually
Application One-time calculation to prove compliance Continuous monitoring with yearly ratings (A–E)
Measures Engine/shaft power limitation, energy-saving retrofits Speed reduction, fuel switching, route optimization
Challenges High retrofit costs, shipyard availability, technical feasibility Data accuracy, voyage planning, maintaining ratings over time
Year Implemented 2023 2023
Compliance Strategy Technical upgrades to meet benchmarks Operational management and planning adjustments
Calculation Calculated once from ship design data Calculated annually from ship reports

Why the Difference Between EEXI and CII Matters

Understanding the difference between EEXI and CII is crucial—not only for compliance but also for long-term operational success and environmental responsibility. Here’s why the distinction is significant:
  • 1. Dual Compliance Strategy:
    EEXI and CII target different facets of emission control. EEXI is a one-time certification that validates whether the ship design meets current energy efficiency standards. CII, however, is a long-term operational performance metric. To be fully compliant, shipowners must address both design inefficiencies (through EEXI) and operational inefficiencies (through CII).
  • 2. Investment and Retrofitting Decisions:
    EEXI may require capital investments in engine limitations or retrofits. CII may prompt investments in voyage optimization tools or switching to low-carbon fuels. Understanding which measure affects what aspect of the ship helps prioritize and budget appropriately. For instance, improving CII may require better crew training and voyage planning rather than new equipment.
  • 3. Commercial and Financial Impact:
    CII ratings are increasingly becoming a factor in charter party agreements and insurance considerations. A vessel with a poor CII rating may struggle to attract cargo, face higher insurance premiums, or suffer from lower resale value. Meanwhile, EEXI non-compliance can delay vessel operations or even result in port detentions.
  • 4. Operational Behavior vs Technical Design:
    A ship with excellent design efficiency (EEXI compliant) can still perform poorly if operated inefficiently, resulting in a poor CII rating. Conversely, a ship with a modest EEXI rating could maintain a good CII score through disciplined operations. Hence, crew behavior, fuel choice, routing, and speed have a critical influence under CII, while EEXI remains fixed post-certification.
  • 5. Preparing for Future IMO Goals:
    Both EEXI and CII are stepping stones toward the IMO’s 2050 vision of zero-carbon shipping. Ships compliant today might still fall short of future regulations. Those who understand the nuances of both indices will be better positioned to anticipate future developments, adopt greener technology, and remain competitive.

Conclusion

The introduction of EEXI and CII marks a turning point for global shipping as the industry accelerates toward environmental sustainability. While both regulations aim to curb emissions, they approach the problem from different angles—EEXI through technical design compliance and CII through operational performance monitoring.

To succeed in this new regulatory environment, shipowners and operators must adopt a holistic view that includes technical upgrades, fuel efficiency, voyage planning, and continuous improvement. Understanding the difference between EEXI and CII is not just a matter of regulatory compliance—it’s a critical business strategy for achieving operational excellence and reducing environmental impact in the long run.

By staying ahead of these regulations and integrating both design and operational efficiencies, the maritime industry can navigate the path toward a greener, more sustainable future.

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