I have a Fred Meyers credit card through US Bank. It offers a $0.03 discount on all fuel sold at their store. Also if I happen to buy a lot on the card in the store, say for food and a TV set, it can give a discount up to $0.35 once, and $0.55 once. This is for a max 35 gallon fill up (for one vehicle). I usually fill my class C with the discount, and use the 3 cent discount for all other fuel purchases.
A 3% discount would be really nice, about 7.5 cents per gallon at the current $2.50 per gallon for gas here in Portland OR.
Good Luck,
Fred.