We also try to pay for all of our fuel with one standard, company issued purchasing card. Our designated bean-counter says that we receive a significant rebate every quarter from the issuing bank on all of our purchases. Sometimes we may lose .05-.10 cents per gallon off of the purchase of certain branded fuel, such as AirBP, however the bean counters say that we make it up with the rebates. I have not attempted to realize this savings on a per gallon basis...

All things considered, I still think it is great that you are measuring/tracking your efforts.