How do naphthenic hydrocarbons differ from aromatic hydrocarbons in crude oil?

In the context of crude oil, naphthenic and aromatic hydrocarbons differ primarily in their chemical structure and saturation:

• Naphthenic Hydrocarbons: These belong to the naphthenic series, which has the general formula $C_n{H}_{2n}$. They are characterized as a saturated closed-ring series. In crude oil, they are important components of all liquid refinery products and are also responsible for forming many of the heavy, asphalt-like residues. Crude oils in which this series predominates are referred to as asphalt-base crudes.123

• Aromatic Hydrocarbons: These belong to the aromatic series, which is an unsaturated closed-ring series. Unlike naphthenes, aromatics are defined by their "special stability" and possess specific electronic and structural properties, often involving a benzene ring as a structural unit. While they are present in all crude oils—with benzene being the most common member—they generally constitute only a small percentage of most crude oil compositions.1452

In summary, while both are ring-based compounds, naphthenes are saturated, whereas aromatics are unsaturated and possess unique chemical stability.41