I have no idea how they do it. Most of the time I come here, their gas is 15-20 cents cheaper than everywhere else around here!
I have been to a variety of Costco gas places in different states, but from what I remember, savings is generally in the 5-10 cents range. Some places you didn't even save anything.
But 15-20 cents? I can't buy gas anywhere else anymore! I have a 3 percent reward on my Bank of America credit card, but I've stopped using it because Costco saves me so much on it's own.
The ONE and only downside to this place, and Costco in general, is that they don't take other credit cards. Would love to get additional rewards on top of the incredible savings! (To clarify, any other cards but AMEX, which I don't have!)