API base stock

base fluid for automotive engine oils. The API (American Petroleum Institute) currently designates five classes of base stocks. These stock types are independent of crude source or processing. Instead, they are based on physical characteristics of the base stock, which are then related to formulated engine oil performance:

Group IContain <90% saturates and/or >0.03% sulfur, with viscosity index ³ 80 and <120. Commonly referred to as conventional, solvent refined base stocks.
Group IIContain ³ 90% saturates and £ 0.03% sulfur, with viscosity index ³ 80 and <120. Commonly referred to as severely hydrotreated and/or hydrocracked base stocks.
Group IIIContain ³ 90% saturates, with £ 0.03% sulfur, with viscosity index ³ 120. Commonly referred to as VHVI or XHVI base stocks.
Group IVPAO’s (polyalphaolefins)
Group VAll other base stocks not included in Groups I, II, III, or IV.(where < stands for less than, £ stands for less than or equal to, ³ stands for greater than or equal to, and > stands for greater than)

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