Applicability: shipowners, ship operators, ship managers, ship masters and manufacturers.

Following the 80th session of the Marine Environment Protection Committee (MEPC 80) in July 2023, the International Maritime Organisation (IMO) has published interim guidance on the calculations of the conversion factor (Cf) for marine biofuels blends. 

Key points of the interim guidance (MEPC.1/Circ.905) are: 

  • For biofuels to be considered “sustainable”, they must be certified by a sustainability certification scheme (e.g., International Sustainability and Carbon Certification (ISCC) or Roundtable on Sustainable Biomaterials (RSB)).

  • They must provide a well-to-wake GHG emissions reduction of at least 65% compared to the well-to-wake emissions of fossil MGO of 94 gCO2e/MJ (i.e. achieving an emissions intensity not exceeding 33 gCO2e/MJ).

  • To determine its Cf value, the well-to-wake GHG emissions value of the fuel mentioned on the sustainability certificate (expressed in gCO2eq/MJ) is multiplied by its lower calorific value (LCV, expressed in MJ/g) for the purpose of regulations 26, 27 and 28 of MARPOL Annex VI.

  • For blends, the Cf should be based on the weighted average of the Cf for the respective amount of fuels by energy.

  • Biofuels not certified as “sustainable” or not fulfilling the well-to-wake emission factor criterion should be assigned a Cf equal to the Cf of the equivalent fossil fuel type. 

Please see Appendix A for a few examples that explain the calculation methodology.

Check your Flag requirements

Although the application date of circular MEPC.1/Circ.905 has been recorded as 1 October 2023, the calculation of the Cf value currently varies between flag Administrations, so ships should check with their respective Flag as to their planned adoption of the MEPC.1/Circ.905. Moreover, this interim guidance will be superseded by a more comprehensive well-to-wake GHG methodology once it is developed based on IMO Life Cycle Analysis (LCA) guidelines. 

Further support and information 

If you are planning to use biofuel blends on your ships, we can provide further advisory support and a comprehensive fuel quality testing service to characterise biofuels to ensure smooth ship operations.

For this support please contact

Download PDF of Class News 18/2023