The discount is 5 cents a gallon at Shell stations with Gold Status when you join Shell's fuel reward program. It's free to join. You maintain Gold status by filling more than 5 gallons at a time at least 6 times every 3 months.
When you have Elite Status with IHG, you can link your member ID of IHG with Shell fuel rewards. For Elite Status it is supposed to be 6 cents off per gallon, yet as of right now, it seems to only taking into account the 5 cent discount instead of 6. The fuel rewards for these two programs do not stack. Other programs will stack in addition to your Gold status or IHG rewards link to the card (like dining at particular restaurants with min spend).
So when you link your IHG card, the way I see it is I don't have spend more than 5 gallons a time for the 5 cent discount. I may PM the program to ask for the 6 cents.
With PenFed cash rewards platinum card it was always 5% off at the pump. So if gas is $3 dollars you'd minus 5 cents then add the 5% discount. I don't know if it's offered anymore from PenFed.
So a gallon would be $2.95 * .05 = 15 cent(ish). Making it around $2.80 a gallon. That's not way cheaper than say, Arco but I personally like Shell gas and don't mind paying the slight extra to almost same price.
Edit: I just checked Fuel Rewards and they are currently at 6 off cents a gallon because of IHG status. It works!
