
Base oils are lubricant grade oils produced either through crude oil refining (mineral base oil) or chemical synthesis processes (synthetic base oil). Depending upon their chemical structure, base oils may be classified as either paraffinic or naphthenic. Base oils are generally obtained from secondary processing units of refineries. Currently, base oils are obtained using two processes: refining of crude oil and synthesis of relatively pure compounds. They are primarily utilized in the manufacture of lubricants. The base oils utilized for the formulation of lubricants are mineral, synthetic, or vegetable-based. The American Petroleum Institute (API) has developed a base oil classification system, which segments the base oils into five major groups (Group I, II, III, IV, and V). These groups are classified on the basis of the percentage of saturates, sulfur content, and viscosity index.