I don’t believe you can choose how much you spend in credits per fill up. It’s $.15 per gallon off per $100 spent at participating grocery store. If you spend $1k, you get $1.50 off per gallon on one fill up. So if gas is $3 a gallon, you pay for $1.50 per gallon. If you spend $2k, you get $3 off per gallon so using the previous example, your fill up would be nearly free (minimum is $.019 per gallon). If you spend $4k, you can fill up two tanks for nearly free, and so on. It depends on how much you need to fill up, ie I’m supporting 8 cars, so I need to do quite a bit to keep them all nearly free each week.