The American Petroleum Institute (API) has categorized base oils into five categories (API 1509, Appendix E). The first three groups are refined from petroleum crude oil. Group IV base oils are full synthetic (polyalphaolefin) oils. Group V is for all other base oils not included in Groups I through IV. Before all the additives are added to the mixture, lubricating oils begin as one or more of these five API groups.
Group I
- Group I base oils are classified as
- less than 90 percent saturates,
- greater than 0.03 percent sulphur
- viscosity-index range of 80 to 120.
- The temperature range for these oils is from 32 to 150 degrees F.
- Group I base oils are solvent-refined — a simpler refining process.
Most cost effective base oils on the market.
Group II
- Group II base oils are defined as being
- more than 90 percent saturates,
- less than 0.03 percent sulphur
- viscosity index range of 80 to 120.
- Manufactured by hydrocracking — complex refining process
- Group II base oils have better antioxidation properties than GP1.
- They also have a clearer colour
Group II base oils are becoming very common on the market today and are priced very close to Group I oils.
Group III
- Group III base oils are greater than 90 percent saturates,
- less than 0.03 percent sulphur
- viscosity index above 120.
- These oils are severely hydrocracked (higher pressure and heat than GP2).
- This longer process is designed to achieve a purer base oil.
Although made from crude oil, Group III base oils are sometimes described as synthesized hydrocarbons, or synthetic technology.
Group IV
Group IV base oils are poly alpha olefins (PAOs). These synthetic base oils are made through a process called synthesizing. They have a much broader temperature range and are great for use in extreme cold conditions and high heat applications.
Group V
Group V base oils are classified as all other base oils, including silicone, phosphate ester, polyalkylene glycol (PAG), polyolester, biolubes, etc. These base oils are at times mixed with other base stocks to enhance the oil’s properties. An example would be a PAO-based compressor oil that is mixed with a polyolester. Esters are common Group V base oils used in different lubricant formulations to improve the properties of the existing base oil. Ester oils can take more abuse at higher temperatures and will provide superior detergency compared to a PAO synthetic base oil, which in turn increases the hours of use.
