Introduction

Petroleum is a complex mixture of hydrocarbons that occur in the Earth in liquid, gaseous, or solid forms. The word

petroleum

is often restricted to the liquid form, but it also includes natural gas and the solid bitumen. The word

petroleum

, or

“rock oil,” derives from the Latin

petra

(rock or stone) and

oleum

(oil) and was first used in 1556 in a treatise published by Georg Bauer [1].