I'm using the Power Service stuff, because I can get it at Wal-Mart and it's cheaper than Howe's, which I've only seen at truckstops. I use a third of the contents of the bottle per tankful. I've used Howe's in the past though and other than the truckstop prices, it seemed to work well. My primary reason for using any of this stuff is to clean the injectors. I've never noticed a difference in fuel mileage using fuel additives.