The XL7500 line is the only Gr. III oils Amsoil has. It indeed is designed for the quick lube market and for those who demand an API certified oil. All their Gr. IV 100% synthetic oil says 100% on the container but due to Amsoil proprietary formulations, they cannot be API certified. In other words, Amsoil would have to down grade their Gr. IV oil to pass API primarily due to the amount of phosphorus they use for extended drains. API limits the level of phosphorus that can be used, supposedly at the request of auto markers who fear catalytic converter problems if the car uses oil.