Base oil is a lubricating naphthenic base oil produced by refining crude oil (known as mineral base oil) or through chemical synthesis (known as synthetic base oil). It exhibits a boiling point within the range of 500°F to 1050°F and consists of hydrocarbons with 18 to 40 carbon atoms. Base oil is generally used to manufacture products such as lubricating grease, motor oil, and metal processing fluids. According to the American Petroleum Institute, these oils are classified into five main categories: Group I, Group II, Group III, Group IV, and Group V on the basis of their percentage of saturates, sulfur content, and viscosity index. Based on their chemical structure, base oils are classified as paraffinic and naphthenic.
Naphthenic base oil is derived from naphthenic crude. It displays a low pour point, contains very little wax, and is therefore highly stable. Moreover, it yields medium viscosity index and low viscosity index base oils which is why it is inexpensive. Naphthenic base oil falls into the Group V category. It is also known as “pale oil” due to its color. Being rich in aromatic hydrocarbons, these oils display a high solvency advantage for certain types of additives. It is also rich in cyclo-paraffins.