Base fluids are needed in order to produce lubricating oils. These base fluids are generally of mineral, vegetable or animal origin or are produced synthetically. They are classified into five so-called API groups:
- Group I-II: Mineral oils
- Group III: Hydroisomerized mineral oils
- Group IV: Poly-alpha-olefins (PAO)
- Group V: All others such as esters, polyalkylene glycols, alkylated naphthalenes, ethylene/propylene co-oligomers and more
The decision as to which base fluid is used in an application depends on the requirements placed on the fully formulated lubricant.