Re: why is oil lighter than water?

Oils are generally less dense than water. The unit weight per volume of 
oil, or density, is less than that of water. The oil then floats. There 
are some oils that are more dense than water and sink into the water. You 
may have read or seen the news of oil spills in the ocean that were 
partially submerged. The density of these spills were close to the density 
of water and make them difficult to clean up.