I know that Amex Preferred gives 6% on groceries but does it also give 6% on co-branded gasoline such as Costco, Vons, Food for Less, or Ralphs. I’ve seen discussions about cards such as Usaa Amex rewards, Discover, or Chase not giving the popular 5% back if the gas is from a co branded store and I was wondering can Amex differentiate between groceries and gas?