How is the classification of base oils used in lubricants made?

The API classification of base oils used in lubricants is the most important determinant of an oil’s performance: But how is the classification of the base stock oils made? In order to fully understand base oil definition we also have to look at the evolution of lubricant base oils.

The history of the development of classification of base oils used in lubricants.

From the time that man first invented machines to reduce manual labour, lubricants have been an essential part of day to day industry. For decades crude oil derived lubricant base oils have been used to formulate lubricants used in various applications. Today the classification of base oils used in lubricants for mineral base oils fall in Groups I & II.

The Second World War saw the development of a new breed of machine called a jet or turbine engine that required a new classification of base oils used in lubricants. Conditions prevailing inside this new machine were so extreme that a new lubricant had to be developed to ensure long term reliability.

Fortunately both the Americans and Germans were already in the early stages of producing Synthetic lubricants. Manufactured by man in a laboratory by reacting long chain alcohols and acids, these lubricant base oils (base fluids) opened a new classification of base oils used in lubricants known as ‘Esters’. From the Ester technology, branched several new synthetic basestocks, including polyolesters, diesters and PAGs. These highly evolved base oil groups were later classified in ‘Group V’.


In the early 70’s, the Mobil Oil Corporation developed and marketed a new type of synthetic lubricant base oil called PAO (polyalphaolefin). This base fluid was derived through a chemical process wherein Ethylene (a mineral oil derivative) was modified to give a final fluid with very good lubricating properties.

With these PAO’s, Mobil formulated the first long life crank case oil for use in motor vehicles. One of the most significant characteristics of PAO is it’s ability to perform at low temperatures, making it ideal for engine oils working in North American and European climates. The PAO classification of base oils used in lubricants were later classified as Group IV lubricant base oils.

Mineral oils that perform similarly to the synthetic classification of base oils used in lubricants.

The mid eighties saw the major oil companies develop a new basestock technology. These new lubricant base oils, while not able to reach performance levels of the Group IV and V ‘synthetics’, were superior to their mineral oil counterparts. This classification of base oils used in lubricants was formed by artificially modifying mineral oils and removing a high percentage of the impurities or weaker molecular structures, inherent in mineral oils.

Different oil companies employ different ultra refining techniques, but essentially all form part of Group III, base fluids. These lubricant base oils are more commonly known as; VHVI, UCBO (unconventional base oils), hydrocracked or hydroisomerised oils. Right or wrong, the classification of base oils used in lubricants in these special Group III base fluids is ‘synthetics’.

Today there are several classification of base oils used in lubricants, ranging from Group I, up to the extreme or ultra performance Group V synthetics (in the truest sense of the word).

Habot Oil, a producer of high quality oils understands the classification of base oils used in lubricants, as well as the impact of this on a lubricants performance. So give the professionals at Habot Oil a call to find out what oil best fits your requirement.