[2] Chemical substances – additives – are added to the base oil in order to meet the quality requirements for the end products in terms of, for example, friction and cleaning properties.
[3] Mineral base oils are first distilled from petroleum, and they comprise the 26-40 carbon fraction.
The reduction in aromatic compounds improves the oxidative stability of the oil, delaying formation of sludge and varnish.
[5] In 1993, the American Petroleum Institute (API), categorized base oils into five main groups.
Chemical and physical characteristics are defined for Groups I through III that reflect how refined they are, correlating in some way to high and low-temperature viscosity, oxidative stability, volatility, and so on.
Originating in 1971, a better grade of petroleum base oil, which may be partially produced by hydrocracking.
Polyalphaolefin oils have a higher oxidative stability in extreme temperatures, and also have exceptionally low pour points, which makes them much more suitable for use in very cold weather (as found in northern Europe), as well as in very hot weather (as in Middle East).
Originating in the 1990s, a more refined grade of petroleum Group II base oil, produced by Hydrotreating.
Poly-internal-olefins (PIO) oils are similar to Poly-alpha-olefins (PAO), but use different chemicals in the synthesis process to obtain an even higher viscosity index (VI)[10]