That is correct. Thier "markup" on gas is about $.03-04 cents per gallon on the few stations that I insure. The bulk of thier profit comes from the "grocery" part of the business.
Even from that they don't make much. I was thinking of opening one and I was shocked to learn that a lot of them were clearing a lot less than I make. Those places aren't the cash cows people think they are. The people that do well with them are the ones that own a bunch.