OK, for the slow people that are horrible at math I will explain this one more time. The Volt gets 360 miles on its gas engine per tank. The Volt also gets 40 miles for every full charge. If your commute is within a 40 mile round trip, then you don't have to use any gas during your commute. A Prius uses gas constantly so it gets over 500 to a tank. OK great.I drive a Prius to work everyday let's say. I have a 50 mile commute. That is 250 miles each week in just work commuting. So no driving at night or weekends that is 2 weeks of driving with a Prius. Same scenario with a Volt.I drive a Volt to work everyday, 50 mile commute. Same 250 miles each week. But I get 40 miles each day on a charge. Assuming I only charge it each night I would only use 10 miles on the engine, the rest would be full electric. So 10 miles a day in one week of work driving is only 50 miles used on the engine. Assuming I don't drive at night or on weekends (same scenario as the Prius). And remember I get 360 miles to that tank of gas. I could commute to work for 7 weeks technically speaking, and still have 10 miles to spare. Are you still with me? Why would GM need to add the extra weight of fuel to a car when it gets 40 miles on full electric. You would fill up the Prius' larger tank a lot more thus spending more. It's simple math.