I spelled it out in a manner I felt was clear: API SP is a standard. It encompasses the engine oil testing protocol found in the SAE J183. This is how oil standards are enacted.
ILSAC is simply a licensing agreement. ILSAC will take an API SP approved product and put their license on it "IF" it meets the resource conserving/energy conserving requirements that they desire. SAE J183 is a performance standard and does not cover fuel economy (RC/EC).
SO, if an oil carries ILSAC GF-6A then it meets API SP and also provides a fuel economy benefit. ALL ILSAC GF-6A oil meet API SP but not all API SP oils carry the ILSAC license. That's as plain as I know to explain it.
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