looking at the Amsoil web site + the use of propriety-bull- tells me that Amsoil like the others use only as much of the more costly PAO base oils, little to no ester oils. they forgot to mention their formulations are for the most profit as well!! i am - was strictly an Amsoil user, but since they are "cheaping out" IMO i will use Redline for my hot air-oil cooled Victory motorcycle + my modified + boosted audi TT, my plane jane 08 colorado will do well on Mobil I which is "supposed" to have some of their own PAO base oil in the mix. being retired i drive about 5,000 miles per vehicle including my 2 motorcycles, yearly changes won't be stressing any quality oil for sure!! i do realize the cheaper Amsoil blends are surely group III base oils with a lesser add pack, i dont feel the xtra additives in signature series + their other costly blends are worth the $$$$