Simple.
Determine what the vehicle type and milage on your vehical actual, the route miles are and fuel price averages. Driver pays for feel and you compensate them for what it should be. Remember get the reciepts. Have a no reciept no fuel comp policy.
So, if your van should average 15 MPG at GASOLINE 4.00/ gal at the pump thats
$ 0.26 per mile. Lets say he has a 500 mile trip at .26 he should spend $ 130.00 to
$ 150.00 max it is reasonable to allow at least $ .01 per mile. for a van .025 for a S/T running Diesel. This is for traffic you will need to pad this comp for inner city work. This is what you pay the driver for fuel unless ofcorse there is a mechanical or other issue.
If you are responsable for maintenance and its proven that a mechanical, terrain or other condition outside of a drivers controll caused exess fuel to be used then compensate the driver otherwise have the driver buy his/her own fuel. This will also help with the driving habbits. If a driver uses less fuel than you estimated dosent idle, reasonable speed, good routing, no exceptions on the freight, consider paying the difference as a bonus. Yeah, its a couple cents a mile but it may help keep a good driver.
Bob Wolf