Summary:
- Oil is a thick, dark brown or black liquid.
- It is found in rock layers of Earth's crust.
- Oil is currently the most commonly used source of energy in the world.
- The United States produces only about one-quarter as much oil as it uses.
- Petroleum is also used to make waxes, plastics, fertilizers, and other products.
- The main oil producing regions in the U.S. are the Gulf of Mexico, Texas, Alaska, and California.
- Oil moves through permeable rock and is trapped by the impermeable cap rock.