For preservation to be successful, these organic remains must be isolated from scavengers by rapid burial, or by deposition in water with a low supply of oxygen. Since marine life is abundant in the shallow waters of continental shelves, and since there is a great deal of sand and clay being deposited in these areas, it is likely that most petroleum formed along continental margins. Once collected, the organic debris is slowly converted to petroleum as temperatures and pressures rise. These conditions convert the organic material into hydrocarbons . When hydrocarbons form, their low density causes them to rise and they move into adjacent permeable rock where they can collect in oil traps .
Petroleum is removed from oil traps by drilling .