We got another $25 in free gas today. We don't use credit cards to get the free gas, but use Speedway's rewards program. It took 17,500 points to get there and we get 500 points for buying a $50 gift card (for $49). They reduced their benefit program this past week, you only get 10 points per gallon of gas. It used to be 10 points per $1 spent on anything, which would get you 23-28 points per gallon based upon the price of gas.
My math shows that when we buy $1250 of gas using $50 gift cards, we get a total of $1275 worth of gas for only $1225. That comes out to a 3.9% discount on gas. I know there's other options with credit that can do better, but we can't get any credit at this time.
One last trick I found by accident last week is that Speedway lists their afternoon gas prices on their web site in the morning. What I plan to do is the morning before I plan on filling up, I'll check the prices to come and see if the current price is better or if I should wait until they adjust the live prices.