How does Oil Form?

Most geologists believe that oil is formed by the preserved remains of prehistoric zooplankton and algae. Over time, they settle on the bottom of the sea, mix with mud, and is buried under layers of sediment. Heat and pressure cause the remains to change into a waxy material, then into liquid and gaseous hydrocarbons. Since the hydrocarbons are lighter than rock and water, they travel upwards, get trapped, and form oil fields.