I agree with American Express charge card. That's what we use and our crew managers each have one. No interest since its a charge card and it gets paid in full each month. Easily tracked on AmEx website, as well as on Quickbooks. Also, we have a fuel log assigned to each truck and trailer. Crew manager has to fill out the log each time they get gas. Date, description, amount in $, gallons, truck mileage, and employee initials are all on the log. Pretty basic. However, this lets us check up on fuel usage, as well as comparing it to numbers that run through quickbooks. All trucks and trailers have their own specific equipment items on them, which is checked each morning. All is accounted for at the end of the day, so nothing can be lost, or in this case, stolen.
Hope this helps. Good luck!