Crude oil, also called petroleum or oil, is a naturally occurring liquid made up of hydrocarbons found in various geological formations around the Earth. It exists in a variety of states. Oil businesses spend trillions of dollars in its extraction, refinement, and trade every year. Petroleum can be used to make many petroleum products. It has been used in some form or another since ancient Mesopotamia. Although advancements have been made toward replacing petroleum with more renewable resources, it remains one of the most widely used forms of energy in the world. The Introduction to Crude Oil training course defies what crude oil is. It describes the different types and characteristics of crude oil and how it is extracted. It also discusses the various uses for crude oil and crude oil products. Introduction to Crude Oil is part of the Petroleum Refining training series.