Driving daily distances up to 40 miles, the Volt is one of the most energy efficient cars on the U.S. market, bested only by a pair of battery electric vehicles, the Nissan Leaf and Mitsubishi 'i' minicar. And when those vehicles run out of energy, it requires several hours to recharge them, while the Volt can keep going indefinitely in just the time it takes to fill its gas tank.
We consider battery electric cars slightly greener than the Volt, because they can travel further with no tailpipe emission at all.
When the Volt switches over to power provided by its gasoline generator, however, the EPA rates it at 37 miles per gallon. That's lower than the 50-mpg combined rating of a Toyota Prius hybrid--meaning that the Volt is better for shorter distances, but the Prius will use less fuel overall if you travel hundreds of miles every day.
While prices vary greatly in different parts of the country, electricity is virtually always a cheaper energy source than gasoline, in part because gasoline engines are notably inefficient at converting the fuel's energy content into forward motion. The environmental impact of running on electricity produced from dirty coal has been studied, with the conclusion being that if you compare to a 50-mpg Prius, there are certain states in which the Prius is marginally cleaner. Compared to the average 25-mpg car, however, and electric running in a Volt is always cleaner on a wells-to-wheels basis.
Using standard 120-Volt household current and the charging cord stowed in the Volt's load bay, a full recharge of the Volt battery takes 8 to 12 hours. That's more than cut in half if you install a 240-Volt charging station, but unlike electric cars with larger packs, that's not an absolute requirement for the Volt if you can charge overnight.