Basically, ILSAC specs are developed by U. S. and Japanese automakers, oil makers, and additive package suppliers, with consideration of near-future emission standards.
When ILSAC has their new spec ready (GF-4 in this case), API takes that and works with European automakers to combine the whole thing into the next API service category. For example, next summer, you won't see an ILSAC GF-4 oil with API SL service category, nor an API-SM 5W-30 GF-3 oil, etc. You'll see API-SM & ILSAC GF-4 on the same bottle of 5W-30. Some viscosity grades don't qualify for ILSAC ratings. American auto makers don't recommend 5W-40 oils in their engines, so those oils won't be ILSAC rated, for example. Ditto for oils designed for diesel engines, even so-called fleet oils.
[ October 02, 2003, 11:27 AM: Message edited by: Ken2 ]