Recovering the oil is difficult and depends upon many factors, including the type of oil spilled, the temperature of the water (in warmer waters, some oil may evaporate), and the types of shorelines and beaches involved. A sheen is usually dispersed (but not cleaned up) with detergents which makes oil settle to the bottom. This BP spill has oils that are denser than water, such as Polychlorinated biphenyls (PCBs), can be more difficult to clean as they make the seabed toxic.