Oil, also officially known as petroleum or crude oil, is a natural, flammable liquid that consists of a mixture of hydrocarbons of various substances and other liquid organic compounds. Oil is found in geologic formations beneath the Earth’s surface. It is a fossil fuel along with natural gas, which is fuel made out of the large quantities of dead organisms, which are usually zooplankton and algae. They are buried beneath sedimentary rock and undergo a process of intense heat and pressure. It is usually excavated by using oil drilling. This latter stage come after the structural geology, sedimentary basin analysis, and reservoir characterization is done around the site. When drilled, it is refined and separated, most easily when heated at boiling point. Oil is used as fuel (petrol, kerosen