API Service Categories
Authority: American Petroleum Institute (API) Engine Oil Licensing and Certification System
API service categories rate gasoline engine oil performance and are updated periodically by the American Petroleum Institute. The current category is API SQ, introduced in March 2025 alongside ILSAC GF-7, superseding API SP (May 2020), which replaced API SN (October 2010) and its LSPI-focused interim update, API SN PLUS (May 2018).
| Category | Introduced | Key Change |
|---|---|---|
| API SQ | March 2025 | Current category; companion to ILSAC GF-7, addressing low-speed pre-ignition, timing-chain wear, high-temperature deposits, and sludge/varnish control |
| API SP | May 2020 | Added low-speed pre-ignition (LSPI) protection, a timing chain wear test, and support for lower-viscosity oils; companion to ILSAC GF-6 |
| API SN PLUS | May 2018 | Interim supplement to API SN adding an LSPI protection requirement for turbocharged gasoline engines, without a full new base category |
| API SN | October 2010 | Full category prior to SP, with tighter limits on sludge, deposits, and oxidation, and compatibility with higher ethanol-content fuels |
How API Categories Work
The American Petroleum Institute assigns two-letter service categories to gasoline engine oils through its Engine Oil Licensing and Certification System (EOLCS): the first letter 'S' denotes 'Spark-ignition' (gasoline) engines, and the second letter advances alphabetically with each new category. Oils that pass the required engine and bench tests for a category can display the API 'starburst' or 'donut' symbol on their label, giving buyers a quick way to confirm an oil meets current performance requirements.
Because engines, fuels, and emissions systems keep changing, API updates categories every several years, usually timed to coincide with a new ILSAC GF specification aimed at passenger cars. Each new category is typically backward-compatible, meaning an oil certified to the newest category can generally be used in older engines designed for a prior category, though the reverse is not true.
What Changed With SP and SQ
API SP, introduced in May 2020, was the first category to directly address low-speed pre-ignition (LSPI), a knocking phenomenon that became more common in modern turbocharged, direct-injection gasoline engines and that can damage pistons and connecting rods. It also added a timing chain wear test and extended support to lower-viscosity oils, which help downsized turbo engines meet fuel-economy targets. An interim supplement, API SN PLUS, had already added the LSPI protection requirement in May 2018 without creating a full new base category.
API SQ, launched in March 2025 alongside the ILSAC GF-7 specification, is the current category. It builds on SP's requirements, continuing to address low-speed pre-ignition and timing-chain wear while adding tighter control of high-temperature piston and turbocharger deposits and sludge and varnish formation, reflecting the continued shift toward smaller, more heavily loaded turbocharged engines.