What is the Energy Efficiency Existing Ship Index (EEXI)?

The Energy Efficiency Existing Ship Index (EEXI) is a measure introduced by the International Maritime Organization (IMO) to assess and improve the energy efficiency of existing ships. It is a numerical value expressed in grams of CO2 emitted per tonne-mile (gCO2/tonne-mile)  that represents the energy efficiency of a ship in relation to its transport work. It requires existing ships to meet a minimum level of energy efficiency. EEXI aims to reduce carbon emissions from global shipping in line with the IMO’s ambition for reducing greenhouse gas emissions. 

What Are The Key Aspects of EEXI Regulations?

The EEXI regulation was adopted by the Marine Environment Protection Committee (MEPC) of the International Maritime Organization (IMO) in June 2021. It is mandatory under the MARPOL Annex VI regulation and applies to all cargo, cruise and LNG carriers above 400 GT engaged in international voyages, except domestic passenger ships, coal ships, nuclear ships and container ships below 4,000 TEU. The EEXI regulation came into force on 1st January 2023. Ships built on or after 2023 are not covered by EEXI but need to comply with EEDI Phase 3 requirements. The specific details of the regulation are quite extensive, but here are key components and provisions typically found in the EEXI Regulation:

  1. The EEXI certification requirements came into effect on November 1, 2022. 
  2. All ships are mandated to compute their Attained Energy Efficiency Existing Ship Index (EEXI).
  3.  This certification, applicable only once, specifically addresses the design parameters of existing ships
  4.  Various technical methods exist to enhance the carbon intensity of these ships and meet the stipulated EEXI standards.
  5.  A review clause necessitates the IMO to assess the effectiveness of EEXI implementation by January 1, 2026, and, if needed, formulate and approve additional amendments.

What are the Requirements for EEXI Compliance?

The required EEXI represents the maximum (least efficient) theoretically allowable EEXI and is based on reference lines formulated for different ship types and sizes. To comply, a ship must:

  1. Calculate attained EEXI based on technical characteristics
  2. Compare attained EEXI vs required EEXI
  3. If attained EEXI ≤ required EEXI, then no further action is needed
  4. If attained EEXI > required EEXI, measures must be implemented to reduce the ship’s carbon intensity to meet required EEXI

What Are the Key Steps that Shipowners Must Take to Comply with EEXI?

  1. Calculate attained EEXI based on EEXI technical file submitted
  2. Identify solutions to reduce EEXI to required level if not compliant 
  3. Update SEEMP with final chosen compliance measures to show how the required EEXI will be achieved.
  4. Install efficiency modifications to achieve required EEXI before 1.1.2023
  5. Update IEE certificate with final EEXI value

How to Calculate EEXI?

EEXI is calculated using a similar formula to EEDI but considers the ship’s historical technical characteristics and operational data at delivery rather than design characteristics.

The formula to calculate the attained EEXI is:

Attained EEXI = (∑nME.CFME,i . SFCME,i . PME,i) / (∑j. Capacity . Vref)


  • ME = Main engine
  • nME = Number of main engines
  • SFC = Certified specific fuel consumption 
  • P = 75% of the rated installed engine power 
  • Vref = Ship reference speed

Example EEXI Calculation:

A 40,000 DWT bulk carrier with 1 main engine of 10,000 kW and 60,000 metric ton deadweight capacity at design draft. Its reference speed is 14 knots.

The certified SFC is 190 g/kWh at 75% main engine power.

∑nME.CFME,i . SFCME,i . PME,i  = 1 x 190 (g/kWh) x 0.75 x 10,000 (kW) = 1,425,000

(∑j. Capacity. Vref ) = 60,000 DWT x 14 knots

Attained EEXI = 1,425,000 / 840,000 = 1.70 g/DWT.nmile

How to Efficiently Implement EEXI?

To efficiently implement EEXI compliance across a fleet of ships, a structured plan should be developed that covers:

  1. Establishing current fleet EEXI performance 
  2. Determining compliant vs non-compliant ships
  3. Identifying feasible compliance options for each ship
  4. Performing cost-benefit analysis on options 
  5. Selection of solutions to be applied to each ship
  6. Planning deployment schedule considering ship schedules/routes
  7. Executing chosen modifications across fleet before deadline

Important Tips for EEXI Implementation

  • Start planning early to avoid rush near deadline
  • Leverage shore power, optimise voyage execution for easy gains
  • Evaluate use of alternative fuels like LNG or biofuels
  • Optimise maintenance to operate equipment at peak efficiency 
  • Consider engine power limitation if limited by attainable EEXI 
  • Use EEXI monitoring tools to continuity track performance

Important Tips for EEXI Implementation

EEXI applies to existing ships while EEDI applies only to new ships. The key differences are:

EEXI is based on a ship’s current efficiency/carbon intensity EEDI is based on design characteristics
EEXI only considers ship’s technical features EEDI also accounts for design efficiency features
EEXI aims to incrementally improve existing ships EEDI works to optimize energy efficiency at newbuild stage

What are the Differences Between EEXI And CII? (EEXI vs CII)

EEXI is a one-time regulation It is a continual improvement mechanism
This is technical measure It focuses on operational measures
It uses a fixed required standard CII grading is relative within peers
It requires one-off modifications It requires ongoing tracking & actions

Role of Shaft Power Limiter and Engine Condition Monitoring in Complying with EEXI Regulation

Shaft Power Limiter (ShaPoLi) and Engine Condition Monitoring Systems (ECMS) are crucial technologies for improving and complying with the Energy Efficiency Existing Ship Index (EEXI) regulation by the International Maritime Organization (IMO). ShaPoLi regulates a ship’s propeller shaft power, optimizing its performance and preventing excessive fuel consumption. This ensures that the vessel operates within the specified EEXI standards. On the other hand, Engine Condition Monitoring System constantly monitors the engine’s condition, identifying inefficiencies and potential issues that may impact fuel efficiency. By addressing these issues promptly, ECMS helps maintain the ship’s overall energy efficiency, contributing to compliance with EEXI regulations. Both technologies play a pivotal role in minimizing fuel consumption, reducing carbon intensity, and meeting the IMO’s environmental sustainability goals in the maritime industry