This is not true. The spilled oil did not go to the bottom of the sea. When oil spills on water it floats on its surface and can break apart into smaller droplets due to wave action. Eventually, microbes use most of the oil as a food source. In the Deepwater Horizon oil spill most of the oil never made it to land because it was broken down by microbes. Some of the oil from the spill did reach the shoreline and was cleaned up through booms and other containment methods.