Seeing as how you can make your own diesel out of old cooking oil, I'm not really seeing the problem with diesels. Railroads are huge diesel users, no one seems to be holding their feet to the fire. Toyota has run their superb D-4D automotive diesel for years, it gets better mileage than the gas motor by about 20%. Amazing it hasn't shown up in their Prius line already. I'd look hard at that Hero.