When dispersants are applied to surface oil slicks, they act to break up the slicks and move the oil, in the form of tiny droplets, from the water surface down into the water column (the volume of water extending from the surface to the bottom).

The diagram below shows how dispersants work:

1. First, the dispersant is applied to the water surface.
2. Next, molecules of the dispersant attach to the oil, causing it to break into droplets.
3. Wave action and turbulence then disperse the oil-dispersant mixture into the water column, so that the oil that had been concentrated at the surface is diluted within the water column.