The International Convention on the Prevention of Pollution from Ships (MARPOL) entered into force in 1973 and has been amended to apply to GHGs. MARPOL rules apply to all ships flying flag of any country that has ratified the measure. Annex VI to MARPOL contains GHG regulations. 88 countries representing over 96% of the world’s merchant fleet (including the US) have ratified Annex VI, which regulates air pollution and GHGs.