There are 5 groups of oils which are used for the production of finished lubricants, these are known as base stocks. basically group I is a refined mineral oil, group II is a highly refined mineral oil group III is a partial synthetic oil, Group IV is a full synthetic mineral oil, and finally group V which is specialist oils. The cost of the base oil increases from group I to group IV, aswell as the performance, consequently group IV products tend only to be used when strictly necessary due to the increased cost (which can be 3 to 4 times that of a group I - but with the performance to meet.

VW 505.0 can be met with a partial synthetic product, sure you will get better performance from a full synthetic, but need to way up the cost benefits.