Oil

Fossil fuels are mixtures of hydrocarbons that formed from the remains of plants and microscopic creatures that lived millions of years ago in a marine environment before the existence of dinosaurs. Over millions of years, the remains of these animals and plants were covered by layers of sand, silt, and rock. Heat and pressure from these layers turned the remains into what we now call crude oil or petroleum. The origin of the word petroleum can be found in the Latin words for “rock” and “oil” (petra  + oleum).

Crude oil is not a single chemical compound but thousands, sometimes hundreds of thousands, of different compounds. They are all generally combinations of hydrogen and carbon atoms, called hydrocarbons. Each of these compounds has its own boiling temperature, and therein lies the most useful and utilized physical phenomenon in the petroleum industry.