I just switched over to using Mobil1 0W-40 (was using 15W-50 in all but trucks), now that I can get it at AutoZoo. Hopefully Wal-Mart will start carrying it near me at a better price. Autozoo get $4.99 for one or $4.79 each for twelve or more. Biggest problem is I think they only get 12 in at a time. It takes 45 quarts to do an oil change on my fleet, so I don't mind buying in bulk. Stuff seems to have cut oil consumption in my Suburban, but we shall see over the long haul.