My commute is much different
My commute is much different than yours, I have not had to buy gas since I bought the car.
In June.
Of last year.
Seriously, I have put 5000 miles on my Volt, and have used less than 2 gallons of the gas that was in it when I bought it. I expect that in June of this year I will have to put some gas in it since the car is programmed to use up gas that is a year old to keep it from going stale. I will follow the owner's manual and only put a few gallons in it at that time. That should be enough for the next year...
Check Voltstat.net for some real world mileage numbers.