FYI. This from an eamil I recieved. So anyone wondering about their base stock. Here is some info. AMSOIL utilizes a full spectrum of only premium synthetic base oils to create its products, which includes PAOs and multiple types of esters. AMSOIL treats synthetic base oils like additives, with each having its own set of unique properties, and combines them to obtain the best performance. Some AMSOIL products contain as many as four different base oils. Specific formulary information is considered proprietary. Some or our products are made with Group III, others are not. Specific formulary information is proprietary.