Oceans are polluted by oil on a daily basis from oil spills, routine shipping, run-offs and dumping.
Oil spills make up about 12% of the oil that enters the ocean. The rest come from shipping travel, drains and dumping.
An oil spill from a tanker is a severe problem because there is such a huge quantity of oil being spilt into one place.
Oil spills cause a very localised problem but can be catastrophic to local marine wildlife such as fish, birds and sea otters.
Oil cannot dissolve in water and forms a thick sludge in the water. This suffocates fish, gets caught in the feathers of marine birds stopping them from flying and blocks light from photosynthetic aquatic plants.