A generic term applied to oil and oil products in all forms, such as crude oil, unfinished oils, petroleum products, natural gas, plant liquids, and non-hydrocarbon compounds blended into finished petroleum products. Complex mixture of naturally occurring hydrocarbon compounds found in rock. Petroleum can range from solid to gas, but the term is generally used to refer to liquid crude oil. Impurities such as sulfur, oxygen and nitrogen are common in petroleum. There is considerable variation in color, gravity, odor, sulfur content and viscosity in petroleum from different areas. The term petroleum is derived from the words petra meaning rock and oleum meaning oil