Real simple and this is what require are crews.
By the way, fleet cards are a great answer for fueling. Many places now, because of hazardous waste rules, not a real option for bulk fuel because of the increased paper work and environmental laws
What we do is :
Fleet card, mandatory od reading is necessary.
For tanks, truck od reading is necessary. (usually can drive at least 100 miles in stop go traffic before gas fill up is necessary. depending on route and required work, gas can fill up around 4 per pair of cans on trucks)
A receipt needs to be turned in to office.
It is made clear that if no receipt is given, that gas is taken out and treated as an advance.
Remeber, in god we trust, everybody else pays.
The receipt thing is the trick. No matter what, you can always reconcile purchases with receipts. Catches the stupid ones all the time.