In the world of oils and auto manufacturers and the EPA, oil specifications have to meet very stringent performance specifications. So to be labeled as meeting those specifications an oil that meets those specs is practically the same quality as any other oil meeting the same specs. One oil can meet the specs less expensively than another oil brand, but, the spec is met. Consumers have no idea how the oils meet specs. Rerefined oils meet the same specs. The oil industry worked for close to 6 years to develop a test for today's GF6/ SP oils. In that time 0W16 was introduced in Honda and Toyota. Until this past May the 0W16 couldn't be labeled as energy conserving because of the lack of a test to qualify the oil, even though the oil fully met or exceeded Honda and Toyota specs. I have seen independent tests on heavy duty oils showing Chevron Delo and Mobil Delvac being the first to fall out of grade. These are 2 very respected oils in the heavy duty engine world. Noone has ever had an oil related failure due to the use of either of these oils. So, what do the tests truly prove? All of Shell/Pennzoil/Quaker synthetic and high mileage oils are made from base stock derived from a process that uses steam from purified water to crack the molecules in methane from natural gas. The base stock is 99.9% pure. Other brands still use base oil from hydrocracking, which is very expensive to perform. Which oil is better in an engine, who knows? A person will be fine using any oil that meets the spec and viscosity grade the manufacturer requires. I personally found in the cylinder deactivation engines, the proper viscosity must be used. I had 5W30 put in a 5.7 Hemi that called for 5W20. After about 390 miles the engine knocked badly. I found the nearest quick lube, had the oil drained and the 5W20 put in and the engine never knocked again. Pick the brand you prefer.