Murphy USA is the owner of the gas service stations in the parking lots of Walmart stores in about 20 states. They have something called Murph e-offers. Just go here and sign up for email offers for coupons. You can also sign up for text message offers(standard texting rates from your carrier will apply) or mail offers. My reader got a free drink coupon and $1 off her next $10 or more fuel up.
Also, Murphy USA offers a 3 cent discount per gallon when paying with a Wal*mart gift card(this is an everyday savings whether you sign up for their e-offers or not.