Petroleum, naphtha or ground oil, natural flammable mineral oil extracted from underground, consisting of hydrocarbons, dense consistency of water, dark colored, unrefined, with its own odor. Hundreds of millions of years ago, animal and plant remains living in the seas or dragged into the seas by the waters formed kerogen similar to crude oil under the necessary conditions (under the effect of heat, pressure and microorganisms) in an anaerobic environment. The kerogen gradually changed during its migration towards the upper layers and formed crude oil. Therefore, the crude oil of no field does not exactly match the crude oil of another field; surely there are more or less differences. This is often the case, even in the same oil field.