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Thursday, 21 May 2015

What Is The Synthetic Base Oil API Group?

Do you know what the synthetic base oil API group is?

Before discussing the synthetic base oil API group it’s interesting to follow the history of synthetic oils: Dr. Hermann Zorn of I.G. Farben Industries in Germany actually began to search for lubricants with the properties of natural oils but without the tendencies to gel or gum when used in an engine environment.

The first real synthetic engine oils appeared for aircraft engines in World War II concurrently in Germany and in the United States. The motivation in Germany was primarily related to resource issues, but also to functional performance requirements. The base oils for aircraft engines in Germany were based on a blend of an adipic acid ester with a poly(ethylene) oil e.g. polymerized olefins/ethylene. Because lower viscosity synthetic oils make engine starting in winter easier and significantly decrease soot deposits in the oil radiator, the US Air Force adopted polyglycols (polypropylene glycol monobutylethers) beginning in March 1944.

The definition of Base Oil is the lubrication grade oils initially produced from refining crude oil (mineral base oil) or through chemical synthesis (synthetic base oil). Base oil is typically defined as oil with a boiling point range between 550 and 1050 F, consisting of hydrocarbons with 18 to 40 carbon atoms. This oil can be either paraffinic or napthenic in nature depending on the chemical structure of the molecule

Understanding the synthetic base oil API group classifications.

Synthetic oil is a lubricant consisting of chemical compounds which are artificially made (synthesized). Synthetic lubricants can be manufactured using chemically modified petroleum components rather than whole crude oil, but can also be synthesized from other raw materials.

Synthetic oil is used as a substitute for lubricant refined from petroleum when operating in extremes of temperature, because it generally provides superior mechanical and chemical properties than those found in traditional mineral oils. Aircraft turbines, for example, require the use of synthetic oils, whereas aircraft piston engines don't. These oils fall into specific synthetic base oil API groups.

Description of the synthetic base oil API groups:

  • Polyalphaolefin (PAO) = American Petroleum Institute (API) Group IV base oil 
  • Synthetic esters, etc = API Group V base oils (non-PAO synthetics, including diesters, polyolesters, alklylated napthlenes, alkyklated benzenes, etc.) 
  • Hydrocracked/Hydroisomerized = API Group III base oils. Petrochemical companies developed processes involving catalytic conversion of feed stocks under pressure in the presence of hydrogen into high quality mineral lubricating oil. In 2005, production of GTL (gas-to-liquid) 
Group III base stocks, the best of which perform much like polyalphaolefin. Group III base stocks, are considered synthetic motor oil only in the United States; elsewhere they are not allowed to be marketed as "synthetic".

Properties of synthetic base oil API groups.

Viscosity Index
Sulphur in %
< 90%
> 0.03%
Conventional (Solvents)
≥ 90%
≤ 0.03%
Requires Hydroprocessing
≥ 90%
≤ 0.03%
Requires severe Hydroprocessing, often special feedstocks

PolyAlphaOlefins (PAO)

All other basestocks not in Group I – IV including other synthetics

Note that the base oil group category is followed by the manufacturing method (in bold print) and then a description of the oil characteristics for each category.

Group I - Solvent Freezing Group 1 base oils are the least refined of all the groups. They are usually a mix of different hydrocarbon chains with little or no uniformity. While some automotive oils on the market use Group I stocks, they are generally used in less demanding applications.

Group II - Hydro processing and Refining Group II base oils are common in mineral based motor oils currently available on the market. They have fair to good performance in lubricating properties such as volatility, oxidative stability and flash/fire points. They have only fair performance in areas such as pour point, cold crank viscosity and extreme pressure wear.

Group – III Hydro processing and Refining Group III base oils are subjected to the highest level of mineral oil refining of the base oil groups. Although they are not chemically engineered, they offer good performance in a wide range of attributes as well as good molecular uniformity and stability. They are commonly mixed with additives and marketed as synthetic or semi-synthetic products. Group III base oils have become more common in America in the last decade.

Group IV - Chemical Reactions The Group IV synthetic base oil API group comprises chemically engineered synthetic base stocks. Polyalphaolefins (PAO's) are a common example of a synthetic base stock. Synthetics, when combined with additives, offer excellent performance over a wide range of lubricating properties. They have very stable chemical compositions and highly uniform molecular chains. Group IV base oils are becoming more common in synthetic and synthetic-blend products for automotive and industrial applications.

Group V - As Indicated Group V base oils are used primarily in the creation of oil additives. Esters and polyolesters are both common Group V base oils used in the formulation of oil additives. Group V oils are generally not used as base oils themselves, but add beneficial properties to other base oils. Some examples of Group V Base Oils are: Alkylated Naphthalene, Esters, Poly-alkylene glycols, Silcones, Polybutenes.

High quality fully synthetic lubricants, such as those produced by Habot Oil, are mostly produced using synthetic base oil API group IV compounds. So make sure, when purchasing synthetic lube, you only buy from reputable manufacturers.