Dispersants can be used to dissipate oil slicks. They may rapidly disperse large amounts of certain oil types from the sea surface by transferring it into the water column. They will cause the oil slick to break up and form water-soluble micelles that are rapidly diluted. Then effectively spread throughout a larger volume of water than the surface from where the oil was dispersed. They can also delay the formation of persistent oil-in-water emulsions. However, laboratory experiments showed that dispersants increased toxic hydrocarbon levels in fish by a factor of up to 100 and may kill fish eggs.
Dispersant Corexit 9527 was for example used to disperse an oil slick in the Gulf of Mexico in 1979 (Ixtoc) over one thousand square miles of sea. The same dispersant was also used in an attempt to clean up the Exxon Valdez oil spill in 1989, though its use was discontinued as there was not enough wave action to mix the dispersant with the oil in the water. During the Deepwater Horizon oil spill in 2010, unprecedented amounts of the dispersants Corexit 9500 and 9527 were used (approximately 7 million liters).