Lubricant used across industry today had its beginning as just a base oil. The American Petroleum Institute (API) categorized base oils by composition and placed them in five categories (API 1509, Appendix E). The first three groups are refined from petroleum crude oil. The fourth group (Group IV) are full synthetic (poly-alpha-olefin) oils. The fifth group, Group V, are all other base oils not included in the early groups. Before engineering and blending takes place, lubricating oils begin as one or more of the five base groups.

Technological advances in the refining of base oils had such an impact over the solvent refining techniques, which saw the API in the early 1990’s, implement a system for describing the various base types. This change saw the further development and introduction of base oil groupings.

Group I base oils are the least refined since they are the result of solvent refining technology which was the primary technique used in refining base oils leading up to 1980. Solvent refining removes the weaker chemical structures in the hydrocarbon chains.

These base oils have an amber or golden colour to them due to impurities that remain in the oil. They typically have a viscosity index, VI, from 90 to 105. Viscosity Index is an empirical figure that describes the change in viscosity with temperature. Group I base oils are the most common type used for industrial oils. Group Ⅱ base oils are becoming more common place in these applications.

Group Ⅱ base oils are produced via the hydrocracking and isomerization technologies to replace the traditional solvent refining process. Hydrogen gas is used to remove undesirable components. The end product is a vast improvement over Group I with a purity level enabling the base oil to last longer in use. Since all of the hydrocarbon molecules of these oils are saturated,

Group Ⅱ base oils have better anti-oxidation properties. These advantages play out through #Better Thermal Stability # Improved Oxidation Stability which in turn results in #Longer service life # Increased component Protection and # Increased resistance to the formation of Sludge and Lacquers.

The API defines the difference between Group II and Group III base oils in terms of the VI, Viscosity Index. This third group have a VI above 120. Group III are also called unconventional base oils (UCBO’s) or very high VI (VHVI) base oils. Group II+ base oils have the same maximum VI as Group II (80-119) however they have a higher minimum VI of 110-119.

Group III are refined even more than Group II base oils as they are subjected to more severe hydrocracking which involves higher pressure and heat.

The lubrication industry has traditionally viewed these oils as PAO’s, poly-alpha-olefins which are created by the synthesizing of oil. The demand for a PAO base oil has grown and some base oil manufacturers began using higher VI feedstocks to make mineral oils with VI’s that matched the PAO’s.

The “new” Group III oils were not manufactured from the small molecules synonymous with traditional synthetic base oils but they bridged the performance gap at a lower cost. This resulted in some manufacturers replacing PAO’s with Group III base oils in their “synthetic” engine oils. This created controversy as the term “synthetic” began to take on a new meaning, because some in the industry believed PAO’s were the only true synthetics. A landmark court case between two lubricant manufacturers in 1999 saw the National Advertising Division of the Council of Better Business Bureau hand down a decision declaring Group III base oils as being “synthetic” because modern base oils produced using hydro isomerization technology had the same performance dynamics as the early synthetics.

Group V base oils are classified as all other base oils including bio-lubes, poly-esters, poly-alkylene glycols (PAG), phosphate ester and silicone etc.

Group V bases are not used as base oils on their own but are used primarily in combination with other base stocks to bring beneficial properties to those other bases. An example would be in the production of a compressor lubricant where synthetic bases are combined to improve the formulation and hence its performance characteristics for its intended use.