Petroleum (from Greek: petra: “rock” and oleum: “oil”) is a naturally occurring, yellow-black liquid found in geological formations beneath the Earth’s surface, which is commonly refined into various types of fuels. Components of petroleum are separated using a technique called fractional distillation.
It consists of hydrocarbons of various molecular weights and other organic compounds. The name petroleum covers both naturally occurring unprocessed crude oil and petroleum products that are made up of refined crude oil. A fossil fuel, petroleum is formed when large quantities of dead organisms, usually zooplankton and algae, are buried underneath sedimentary rock and subjected to both intense heat and pressure.