Castrol TWS only sold at BMW dealerships is an Ester base oil. The other Castrol 10w-60's available retail are PAO base. Castrol Edge 10w-60 may be TWS in markets where TWS isn't available. You'll have to look at the API rating.
TWS is no joke.
Search Doug Hillary on BITOG. He was party to the development of the precursor of Castrol TWS going back to the late 70's and has a tremendous amount of experience with the development/testing of Castrol and Mobil lubricants.
Last edited by Socom; 01-20-2011 at 10:44 AM.