Pennzoil oil today is NOT the same Pennzoil of yesterday, just as Quaker State today is NOT the same Quaker State of yesterday, oil have changed but as companys go, Shell is still Shell along with Pennz and Quaker State both being part of Shell also now! S O P U S This is like arguing about the difference between Texaco and Chevron today(and Shell a few years ago when Texaco was partnered up with them-Equalon) they are now the same company and has anyone really found much difference in their oils now to justify the difference in price or brand? Personally I have never used Pennzoil(yes to QS) after all the sludging I saw in the 60/70's with the customers who used it(and yes they for the most part swar by it-in fact my dad was not allowed to even sell it because of his lease with Richfeild/ARCO and hid it in the back room out of sight so we could have it on hand for the diehards that wanted to buy it) that came into my dad's gas station along with the bad Pennzoil I found that had seperated in their cans around 1967-68. Sure Pennzoil made good on it to us by replacing the bad can we saved to show them with 6 new cans but they never did tell us what had happened and I swar I would NEVER use the stuff which I never have. I have never seen anyone else's oil seperate like it did and yes I have seen left over residues in freshly emptied qts but never clear fluid coming out with a honey colored thick(appox 2 to 3in thick)paste left in the bottom- we had 2 to 3 cases that we had not opened yet(back when cases were still 24 cans each) -10w30- that they also replaced one for one. Pennzoil - NOT ME!!!!