Elemental and Chemical Compositions

As mentioned, petroleum is not a uniform material. Prior to refining, crude oils contain some amounts of dissolved gas, water, inorganic salts, and dirt. After these are removed, most of the remaining compounds are hydrocarbons, some of which contain hetero-atoms—mostly sulfur, oxygen, and nitrogen, and trace amounts of metals (Ni, V, Fe, Cu, etc.). The heteroatom-containing hydrocarbons are often referred to as “non-hydrocarbons” although “hydrocarbons” is commonly used as a general term to include both hydrocarbons and non-hydrocarbons.