Base Oils Classification

A lubricating oil consists of 60-90% base oils and a variable percentage of additives. They are primarily hydrocarbons or molecules of hydrogen and carbon. Their classification provided by the American Petroleum Institute (API) consists of 5 groups. The first three result from the refining and direct processing of crude oil, the fourth is completely synthetic (Polyalphaolefins), and group V includes all the bases that do not fall into other groups. The parameters used for classifying the various groups are: 1. Saturated compounds (the higher they are, the greater the molecular chemical stability), 2. Sulphur (a low content reduces the potential effect of an aggressive acid environment for components and materials or DPFs), 3. Viscosity index (which evaluates the behaviour of viscosity as the temperature changes).

• Group I: base oil with quantities of saturated compounds lower than 90%, more than 0.03% sulphur, and a viscosity index between 80 and 120.
• Group II: base oil with quantities of saturated compounds greater than 90%, less than 0.03% sulphur, and a viscosity index between 80 and 120. It undergoes a hydrocracking process more extreme than Group I, compared to which it guarantees better performance and antioxidant properties.
• Group III: base oil with quantities of saturated compounds greater than 90%, less than 0.03% sulphur, and a viscosity index greater than 120. It undergoes a hydrocracking process even more extreme and at high pressure than Group II Base Oils and are sometimes referred to as synthetic hydrocarbons. It should be clarified that “synthetic oil” is not a technical term, but a commercial one. Legally, in many countries, an oil formulated with Group III bases may be labelled as “synthetic.”
• Group IV: so-called Poly Alpha Olefins (PAO). It is synthetic based made by a synthesis process. It is a very stable base with excellent cold fluidity.
• Group V: it encompasses all the bases not included in the first four groups, including di-ester, silicone, Poly-Alkylene Glycol (PAG base oils), Polyolester (POE base oils) etc. These oil bases can be mixed with others to improve performance, for example Alpha-Tech® technology by Pakelo combines ester bases and group IV bases (PAO). 

People often talk about mineral, semi synthetic or synthetic oil, but what does it really mean? These are only commercial names, not officially standardized, used for the classification of base oils, which vary according to the manufacturer producing oils. Typically, the Group I and II bases are considered mineral, while those of Group III and IV are considered synthetic. The Group V bases may be classified as synthetic, of animal and/or vegetable origin, depending on the origin and the processing /refining processes undergone.