How Long Will A Ventrac 4500Y Run On A Tank Of Fuel?

This is my Ventrav 4500Y tractor with a Kubota 25 HP diesel engine. The Ventrac 4500 holds 6 gallons of fuel. I had the fuel toped off and ran the machine almost 6 hours on 5 gallons of fuel. I would say you could maybe get 7 hours run time if you ran the tank empty. 6 hours of run time would be a good average.