Petroleum (literally rock oil, from the Greek petra- for rock and Latin -oleum for oil) is a general
term used to refer to all forms of oil and natural gas that is mined from the earth. What most people
concern themselves with is crude oil, the liquid mixture of naturally occurring hydrocarbons and
natural gas, which is a gaseous mixture of naturally occurring hydrocarbons.
Hydrocarbons are complex molecules that are formed from long strings of hydrogen and carbon,
such as propane (C3H8) or butane (C4H10).