The average sulphur content of heavy fuel oil (HFO) used for marine diesel engines is 2.7% today. This will undoubtedly change with the coming emission legislation, which will lower the emission limits of SO_x, NO_x, particulate, HC, CO and CO₂. See also list of abbreviations.

So far, the authorities have reduced the SO_x content in the exhaust gas by introducing limits on the content of sulphur in the heavy fuel (HFO) used. This is a much more efficient and straightforward solution, obtained from the refining process, than the installation of separate SO_x cleaning techniques on board each vessel.