Establishing the EEOI and further aspects

The basic expression for EEOI for a voyage is defined as:

The guidelines allow averaging of EEOI over a number of voyages. Where the average of the indicator for a period or for a number of voyages is obtained, the EEOI is calculated as:


  • j is the fuel type;
  • i is the voyage number;
  • FCij is the mass of consumed fuel j at voyage i;
  • CFj is the fuel mass to CO2 mass conversion factor for fuel j;
  • mcargo is cargo carried (tonnes) or work done (number of TEU or passengers) or gross tonnage for passenger ships; and
  • D is the distance in nautical miles corresponding to the cargo carried or work done.

Data sources: Primary data sources selected could be the ship’s log-book (bridge log-book, engine log-book, deck log-book and other official records). It is important that sufficient information is collected on the ship with regard to fuel type and quantity, distance travelled and cargo type so that a realistic assessment can be generated. Amount and type of fuel used (bunker delivery notes or other sources) and distance travelled (according to the ship’s log-book or other sources) need to be documented by the ship on a consistent basis. The whole process may be automated if possible (MariEMS 2017).

The EEOI should be a representative value of the energy efficiency of the ship operation over a consistent period which represents the overall trading pattern of the vessel. In order to establish the EEOI, the following main steps will generally be needed:

  • Define the period for which the EEOI is calculated
  • Define data sources for data collection
  • Collect data
  • Convert data to appropriate format; and finally
  • Calculate EEOI.