We always hear certain brands used Group 2 base oils, others Base 2+, for regular (non-synthetic) oil brands. Just wondering which brands use highest quality base stocks ?. For regular oil would Group 2+ be the best base stock used ?, I never hear Group 3 or higher being used in regular non-synthetic brands. Could someone list which brands are known for using higher quality base stocks ?. Mainly checking the basic store shelf brands such as Castrol, Penzoil, Quaker State, Mobil, Havoline, etc..... . Any info would be appreciated, thanks.