This would make great sence if the tugs would use ethanol (E85) or some other kind of friendly fuel, but if they would diesel or normal gasoline I dont think it'll make much of a difference.
Then there is the shortage of E85 in the world today, Sweden is a good example, since the Saab 9-5 Biopower started to sell in extreme numbers there has been a constant shortage of E85 at gas-stations all over the country...