Technically speaking, Pennzoil MAY be the same as Merc/Quicksilver, but I know that while Ive run nothing but Merc oils over the years, Ive had no engine problems of any kind. I also know that when others have had issues, there was a question about what oil was run.Im a bean-counter–and I did a quick cost benefit analysis, and if you assume you run 50 gallons of oil per year (way more than most), and you buy it at $20/gallon bulk price from your dealer, thats $1K on oil. If you save $5/gallon with cheaper oil, and nothing happens, you save $250. Thats it. Most recreational anglers will never save that in a year. Just not worth the risk for me. Im running Merc/Quicksilver Premium Plus in my 250 Pro XS.Mike Whitten/Germantown, TN