EEOI (Energy Efficiency Operational Indicator)

The Energy Efficiency Operational Indicator (EEOI) is the IMO’s voluntary operational carbon-intensity metric, defined in MEPC.1/Circ.684 issued 17 August 2009. It is the mass of CO2 emitted per unit of actual transport work: sum of fuel mass times each fuel’s carbon factor, divided by cargo carried times distance, in grams CO2 per tonne-mile. Unlike the deadweight-based AER, EEOI uses real cargo carried, so it reflects true utilization but needs voyage-level cargo data. It predates the mandatory CII and informed its design, though the CII regime adopted the simpler capacity-based form for most ship types.