I had run Mobile oil 0w-40 for a decade, switched over to the Shell Helix for awhile, but that got hard to acquire so went with the Penzoil Platinum 5w-40 for awhile. ( Croosfire Limited and SRT6, and a CLK 500) I like the idea of natural gas clean base, but have found it burns off as you drive. After 6,000 miles you will be 0.5 to 1.0 qrts lower than where you started. I have switched to 5w-40 AMSOIL, but will look into the Quaker State oil mentioned above.