Among the biggest obstacles to progress is that, to date, no practicable method exists for assigning the emissions from a transnational voyage to an individual country. Bunker oil is considered a particularly toxic fuel.) January 2016 was the date set for implementation of “tier III” NOx standards in existing emission control areas (ECAs), and as of 2020 the global sulphur cap will be reduced further to 5 000 ppm (Marpol Convention, Annex VI).