Big polluters: one massive container ship equals 50 million cars | Geography in the classroom |

"In international waters ship emissions remains one of the least regulated parts of our global transportation system. The fuel used in ships is waste oil, basically what is left over after the crude oil refining process. It is the same as asphalt and is so thick that when cold it can be walked upon . It's the cheapest and most polluting fuel available and the world's 90,000 ships chew through an astonishing 7.29 million barrels of it each day, or more than 84% of all exported oil production from Saudi Arabia, the worlds largest oil exporter."