IMO Annex VI Regulations and Baselines

Nitrogen oxides

Nitrogen oxides MARPOL Annex VI limits the NOX emissions of marine engines. The figure below depicts the emission limits for the respective Tiers. The limit value depends on the rated engine speed above 130 rpm.

Figure: IMO Annex VI NOX Limit Value (g/kWh)

Since the introduction of ESI in 2011 requirements have come into force for new ships to install Tier II and Tier III engines respectively. However, the ESI Working Group has decided to maintain for the next few years the Tier I levels as a baseline for the purpose of calculating the ESI NOX score.

n < 130 130 ≤ n < 2 000 ≥ 2 000 RPM
Limit Value 17 45*n^-0.2 9.8 g/kWh


Sulphur oxides

Lower limits for fuel sulphur content from the revised Annex VI to the MARPOL Convention have and will come into effect, as shown in the Table below.

Table : MARPOL Annex VI Sulphur Limit % (m/m) in Fuel


Date High Sea (HFO) SOX ECA (MDO/Gasoil)  
2012 3.50 1.00 % S (m/m)
2015 0.10 % S (m/m)
2020 0.50 % S (m/m)

The baselines for ESI SOX are in line with the limit values set by IMO and that determined by the ESI working group. IMO limit values are in place for fuels that would normally be used at the High Seas and in (S)ECA’s and these will be tightened in accordance with IMO regulations. In addition there is another baseline for MDO/Gasoil set by the ESI Working Group at 0.50 % sulphur which will be maintained for the next few years.

The limit value of the sulphur content for fuel used at the High Seas (HFO - HIGH) changed to 3.50 % (m/m) on 1 January 2012; the limit value for fuel used in SOX-ECA (MDO/Gasoil - LOW) changed to 0.10 % (m/m) on 1 January 2015.

Consequently from 1 January 2015 the percentages 3.50, 0.50 and 0.10 are the base lines for the fuels of the categories HIGH, MID and LOW, respectively.

Abatement technologies

In the case of NOX emissions, it should be noted that where IMO approved abatement technologies of primary or secondary nature are applied, their effects have been included in the respective EIAPP certificate(s) issued.
For ESI SOX the equivalent sulphur values for use with approved exhaust gas cleaning system may be used for calculation purposes.