All organic material does not turn into oil. Certain geological conditions must exist within the oil-rich rocks. Under these conditions, only two percent of the organic material is transformed into oil. A typical petroleum reservoir is mostly sandstone or limestone in which oil is trapped. The oil in it may be as thin as gasoline or as thick as tar.
Petroleum is called a nonrenewable energy source because it takes millions of years to form.
We cannot make new petroleum reserves. History of Oil People have used petroleum since ancient times. The ancient Chinese and Egyptians burned oil for lighting. Before the 1850s, Americans often used whale oil for light. When whale oil became scarce, people began looking for other oil sources.