Oil is formed a lot like coal except coal is found on land and oil is mainly found in the ocean. Oil forms from dead plant and animal life drifting to the bottom of the ocean and it there is covered with sand and sediment material. Over thousands of years due to high temperature and pressure these fossils form oil.
Oil ships can carry up to 500 000 tons of oil. So as you can image if one of these ships started to leak it would have a serious detrimental effect on the environment. Oil spills can cover a massive area. It took a long time for this region to recover. To prevent oil spills, I feel oil companies must be so accurate that every part of the tanker is leak proof. There should also have a clean up crew ready if there is a oil spill.