Neighbor is a "Stasher" like all of use Anyway, he is towards the end of his 2 year going stash, last year he got a new vehicle (poor guy, had to trade in his toy for a more family friendly car since he now has a baby), anyway his old car took 5 quarts of oil, this one only takes 4...its a 2009 impala He used to buy 5-6 at a time, and now he has 1 qt left of... 5w30 Royal Purple 5w30 M1 5w30 Amsoil and 5w30 QSUD LOL ANYWAY His idea is, that they will all mix together JUST FINE, and run good for his 6k interval he does. Idk if I should stop him or what? Lol, usually if I have a little of ANY oil left over in a qt, jug etc, it gets demoted to lawnmower, chainsaw blade, anything that doesnt use much and my life dont depend on to get me to work everyday. Regardless, I have heard of 2 brands being mixed or w/e but 4 different brands? theyre all SN grade oils, all the same weight, so this shouldnt be a problem? I just dont wanna go tell another guy what to do under the hood, great way to get knocked out ya know.