You can add a Volt if you want, but it won't work well here and we don't display them in the public listings. The problem is that we don't track kilowatt hours, so MPG doesn't give you an accurate picture of efficiency. We talk a little more about it in the FAQ: What vehicles won't work at Fuelly?
So until we find a way to track electricity usage and factor that into the fuel economy numbers for the Volt, we aren't going to support it. Sorry about that.
I see no problem with keeping these vehicles in to track their fuel use, every one knows that the higher the MPG's they get must mean that they run on a higher percentage of plug-in electric power. Nothing wrong with that even if we can't yet quantify their Kwh usage.
It does show how much less petrol/gasoline people use with these type of cars which is one of the reasons many people are interested in them.
How does the epa calculate MPG equivalent for the windows sticker? If there was somewhere to input maybe weekly kW usage, you could display that alongside fuel usage, so if someone has a higher mpg, you would see the accompanying higher kW usage, whereas someone who has lower mpg might have a lower kW usage too. I suppose that doesn't take into account the length of someone's trip, or percentage of driving under electric only power...