Umm, Quaker State is part of SOPUS, which also has Shell and Pennzoil Brands (among others)...Really? The whole argument about sludging was from years ago when they used Pennsylvania crude almost exclusively. Pennsylvania crude has a very high paraffin wax content, both Pennzoil and Quaker State suffered sludging because of this; Pennzoil offset the issue with massive amounts of detergents IIRC. The wax issue has been remedied by a dewaxing process during the refining. I would not hesitate to run any oil with "dexos" on the label as that is a pretty rigorous standard, and I want to remember it has a sludging component.