Crude oil is a naturally occurring liquid found beneath the Earth's surface that is comprised mainly of hydrocarbons. It is extracted through drilling wells into areas where geologists have identified oil is located below ground. Once a steady flow of oil has been detected at a certain depth, the crude oil can then be extracted out of the ground. The top crude oil producing countries in 2016 were Saudi Arabia, Russia, the USA, Iraq, China, Canada, Iran, Kuwait, UAE, and Venezuela.