There was a time when a 10W30 used in the right conditions made a lot of sense and was a good quality oil . Today , I believe all oil companies have shifted their R&D resources to 5W30 , 0W30, 0W20 , etc. which get all of the best base stocks , additives and research. Mobil 1 , Pennzoil , Valvoline and others are not focused at all on 10W30 oils and use what ever 2nd tier base stocks and additives just enough to meet the spec. and that is all. As a former fan of 10w30 I moved on to 0W30 / 5W30 synthetic oils as being the better quality oils produced by major oil companies today and never looked back .