I checked out Mobil1's site and it says that we can use 5w-30, standard, extended performance, or truck & suv for their "ultimate" level of performance. I used to use only Amsoil 2000 Series 0w-30 and was extremely happy with it, but I've since switched to Mobil1 (which costs me about half what I was paying for Amsoil) and I haven't noticed any degradation. I've used both standard and truck & suv formulas.