Hey guys. I'm just wondering if this is possible, or just something strange is going on. I've been using Shell 93 in my car about a year or so (convenient gas station, plus I know it is quality). I was just about out of gas and decided to fill up at Costco while I was there. Used Costco 93. Now, I usually get anywhere between 330 - 360 miles on a tank, giver or take a few miles (this is not an exact science) However, I only got about 290something out of the tank of Costco fuel. With all the commercials for Nitrogen Enriched, Invigorate, STP, etc is it possible that these "Premium" fuels burn more efficiently?