Two standards, one goal
API SP and ILSAC GF-6 are closely linked gasoline-engine oil standards that still appear in many manuals and on many labels. API SP comes from the American Petroleum Institute and focuses on engine protection. ILSAC GF-6 comes from a joint industry committee and builds on the API category by adding fuel-economy requirements.
In practice, an oil that meets ILSAC GF-6 also meets the matching API SP requirements. You can think of API SP as the protection foundation and ILSAC GF-6 as that foundation plus extra fuel-economy testing.
API SQ and ILSAC GF-7 are the newer family. If your bottle shows API SQ, GF-7A, GF-7B, Starburst, or Shield language, read the API SQ and ILSAC GF-7 explainer before treating it as a match for an older manual.
What each standard adds
API SP brought stronger protection in areas that matter for modern engines. It addresses low-speed pre-ignition, often called LSPI, which can stress turbocharged gasoline direct-injection engines. It also targets timing-chain wear protection and improved control of deposits and sludge.
ILSAC GF-6 takes those protections and adds requirements aimed at fuel economy and keeping that economy stable over the oil’s life. GF-6 is split into two categories. GF-6A covers the common viscosity grades and is designed to be backward-compatible with earlier ILSAC oils. GF-6B is a separate category made for certain lower-viscosity oils and is not backward-compatible, so it should only be used where specifically required.
Why viscosity is still separate
It is easy to mix up a specification with a viscosity grade, but they are different things. A specification like API SP or ILSAC GF-6 describes how the oil performs and what tests it passed. A viscosity grade, such as 0W-20 or 5W-30, describes how the oil flows when cold and hot.
A single oil carries both: a grade and one or more specs. Your owner’s manual will list the grade and the specification your engine needs. Match both, and you have chosen correctly. Meeting the spec but using the wrong grade, or the reverse, still misses what the engine was designed for.