content: I've always liked Royal purple. It just last longer compared to other synthetic oils, making it cheaper in the long run. I get around 15-18K between oil changes in my Expedition. I do swap out the K&N; oil filter every 6k or so miles. I do so an increase in Highway mpg with the Royal purple vs what the Ford comes with.In my other two 4 banger cars, I don't see any MPG improvements, but the once a year oil changes are great.