is gasoline and diesel engine oil quality levels established by API, with technical input from SAE and ASTM. API Service Categories are as follows.

Service Station Oils (Spark Ignited Engine).
Commercial Oils (Compression Ignited Engine).

SA	straight mineral oil (no additives)
SB	anti-oxidant, anti-scuff, but non-detergent
SC	protection against high- and low-temperature deposits, wear, rust, and corrosion; meets car makers’ warranty requirements for 1964-1967 models
SD	improved protection over SC oils; meets warranty requirements for 1968-1971 models
SE	improved protection over SD oils; meets warranty requirements for 1972-1980 models
SF	improved anti-wear and anti-oxidation; meets warranty requirements for 1980 and later models
SG	improved sludge control; meets warranty requirements for 1989 and newer domestic vehicles.
SH	utilizes API SG testing limits but incorporates statistical engine testing requirements and other stringent guidelines for enhanced product quality; SH quality is specified for 1994 and later-model-year vehicles.
JS	1997 Gasoline Engine Maintenance Service. Engine oils developed for this category exceed API SJ.
CA	light-duty service; meets obsolete* Military Specification MIL-L-21.
CB	moderate-duty; meets obsolete* MIL-L-2104A, Supplement 1.
CC	moderate-to-severe duty; meets obsolete* Military Specification MIL-L-2104B.
CD	severe duty; high protection against high- and low-temperature deposits, wear, rust, corrosion; meets Military Specification MIL-L-2104C and D.
CD-II	meets CD plus Detroit Diesel 6V-53T engine test requirements.
CE	severe duty; high protection against high- and low-temperature deposits, wear, rust, corrosion; meets MIL-L-2104C and D, Mack Trucks T-6 and T-7 (EO-K/2), Cummins NTC 400.
CF-2	Severe duty two-stroke-cycle diesel engine service; supercedes API CD-II and may be used where API CD-II is recommended.
CF-4	severest duty; designed for new emission control, high-speed, four-cycle diesel engines; provides improved control of oil consumption and piston deposits.
CG-4	Severest duty diesel engine service for use in high-speed four-stroke diesel engines, especially 1994 and later models meeting 1994 exhaust emission standards. May be used in engines requiring API CD, CE.

*obsolete for military use, but remains valid description of API Service Category.