Don't buy the Royal Purple hype. I've been a Mobil 1 user on several different vehicles for many years now. An '01 Suburban, '05 Grand Caravan, '06 Silverado 5.3, '07 Silverado 5.3, and fairly soon, a '11 Toyota Tundra 5.7. On the two Silverado's I decided to trust the engine oil monitoring system and only change the oil when it got close to the 0% mark, anywhere from around 9000 miles to 12000 miles. On the '07, I got talked into trying the Royal Purple, so I bought a case (two oil changes worth) and a couple Royal Purple oil filters. Liked the literature on the filters, and they weren't any higher than other premium filters, but the oil offered me 0% difference in fuel economy. My '07 had the high end electronics where you could see instant mileage readings, as well as mileage per tank, every tank. I've always watched those numbers, on a quest for better mileage in my trucks, and the Royal Purple offered no better mileage, and I even felt that my mileage might have slightly dropped. And I don't even buy the fancy Mobil 1, just the regular full sythetic that you get at Wal-Mart in the 5 quart jugs, plus an extra quart for the Silverado. I'm not saying Royal Purple is a "bad" oil, just not any better than Mobil 1 in my opinion, and definately not worth the higher price.