The natural form of oil is called crude oil. Oil is developed from once living organisms that were transformed over geologic time into hydrocarbons from heat and pressure as the organisms were being buried and lithified. Straight from the earth, crude oil contains hydrocarbons plus small amounts of oxygen, nitrogen, sulfur, salt, water, and trace amounts of certain metals. Oil is found primarily in sedimentary rocks including limestone, sandstone, and shale. Crude oil is found in varying viscosities (thickness) depending on variabilities in the environment in which it was formed. The types and thickness of oil is determined by the number of carbon atoms that make up the hydrocarbon chain molecule. The more carbon atoms the thicker the oil. Oil refineries, using heating and distillation processes, break up long-chain hydrocarbons and separate crude oil into gasoline, diesel fuel, kerosene, lubricating oils, waxes and asphalt. After further processing at petrochemical plants, crude oil can be converted to fertilizer and plastics. Note that "bedrock" is the solid rock that underlies loose materials such as dirt, clay, sand, and gravel on the surface of the ground. Oil is ALWAYS found below bedrock. Oil cannot be found at any depth below about 30,000 feet. Large oil/gas discoveries have been found at just a few hundred feet in Appalachia, whereas offshore drilling prospects in say the gulf coast could reach depths of 20,000 feet or more. And this whole process of oil formation is classified into two, the biogenic process and abiogenic process. Biogenic meaning formation from decomposition of dead and decayed matter (organically formed), while Abiogenic is the formation from deposited minerals gotten from the earth itself (inorganically formed).