Okay, so here's how it works. Every once in awhile giant food markets in our area runs a special where they will provide anywhere from 2 times to as much as 5 times reward points for gas if you purchase Visa gift cards. So at that moment in time people go crazy buying Visa gift cards. Typically they buy the $500 gift cards and fund them with $500 and it costs $5.95 so for $500 plus the $5.95 you get a $500 Visa gift card but depending on whether it's 2, 3, 4 or 5 times reward points you get 1,000, 1,500, 2,000 or even 2,500 points for your $505.95 spent.
Now, at the gas pump every hundred points reduces your gas price on 25 gallons by 10 cents per gallon so if the gas is $2.889 a gallon 2,900 points get you a one time 25 gallons of gas for free at the pump! Since the gift cards are like cash or a Visa Credit Card you can use them to pay bills online, shop online or in retail establishments, or restaurants.
So after you amass a large volume of points, you can drive up to the pump, scan your gas rewards card at the pump, and then it tells you how much reduction to the price of the gas you're eligible for based on the number of points you have. You then swipe your credit card and the pump price changes to the reduced price. For me it's always the full price of the gas pumped, so the pump price right on the screen drops to $0.000. Right now I have about 50,000 points collectively. So 50000 points / 2,900 = 17.24, meaning I can fill my tank with 25 gallons of gas over 17 times and not pay a penny at the pump.
Below are the rewards points on 1 of the three cards I have. The other two cards have approximately 24,000 points collectively as well.
You can see my purchase on Thursday (2nd receipt immediately above), cost me absolutely nothing at the pump. Those points (and the 25 gallons of regular gas they bought me), cost me just $11.90 in Visa Gift Card activation fees!.