Regulating the type of fuel merchant ships use is difficult since most ships fly “flags of convenience.” While owned by corporations in advanced nations, their ships are actually registered in countries like Panama and Liberia which have no requirements about anything.
Ships began flying flags of convenience during the American civil war when fast and deadly Confederate commerce raiders (built in Great Britain) began to sink huge numbers of ships belonging to New England ship owners and other Union states. These ship owners began to register their ships in Liberia, a colony founded in Africa in 1820 by American philanthropists. (Now a country of the same name).
Great Britain ended up paying the United States over twelve million dollars in gold for damages caused by the Confederate raiders built in the UK and illegally sold to the Confederacy.
[Image courtesy of Wikimedia.]