That's what the official Chevrolet website dedicated to the extended-range plug-in is calculating. The spinning meter (you can kill some valuable time watching it) says Volt drivers have cumulatively tallied just over 100-million miles (the data is constantly updated, live, from the cars out there). Out of those, over 63 million were powered from electricity, as opposed to the gas that's used to power the car's on-board generator once the juice runs out.
The upshot, according to Chevy, is that Volt drivers have saved 3.32 million gallons of fuel compared to all-gas driving. At today's fuel prices, that adds up to about $10 million, according to AAA's latest gas-price survey. GM is looking to further generate sales momentum for the Volt. Model sales through the first half of the year totaled 8,817 units, or about 1,100 more than Chevy sold all of last year.