Most Murphy USA stations give you 10 cents off gasoline using a Walmart gift card, and 15 cents off using a Walmart credit card. Don't know if they sell diesel, as we don't use it.
We have a Chase cash-back card that gives 5% on gas purchases during two of the four quarters of the year. but their exclusions list is such that most every gas station is listed as a "convenience store" and doesn't qualify.
We use Gas Buddy for pricing and Google Maps or Google Earth to see whether we can get in and out easily, and then whatever card has the most potential for cash back or discount. It all adds up.
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