What Walmart credit card could I apply for that I can use at Murphy USA gas pumps for the discounted price?  

Valero has a tiered rebates system. You earn 4¢ per gallon on every gallon purchased when you purchase at least 50 gallons per billing cycle or earn 8¢ per gallon on every gallon purchased when you purchase at least 75 gallons per billing cycle (up to a maximum of 110 gallons). Gas rebates will automatically appear on your monthly billing statement. For more traditional and easy to understand reward options, see general rewards credit cards and especially cash back cards. Those give you simple cash back every time you purchase anything anywhere and rewards are also redeemable everywhere.

If you have an excellent credit there are a lot of credit cards that will bring you more benefits than JCPenney rewards credit card. If you want to save on shopping with a credit card at your favorite stores, you may choose a regular credit card with cash back rewards.

Consider frequent flyer credit cards to earn miles and enjoy air travel benefits. Study the features associated with these credit cards carefully. Hope you will find the credit card right for you.