If you have a car that both plugs in and runs on a conventional engine, what's the mix of miles done on grid power versus gasoline?

You might think it's something like 50-50.

In the case of the Toyota Prius Plug-In Hybrid, with an electric range of 6 to 15 miles, that's probably about right--especially in the kind of low-speed, stop-and-go urban driving where hybrids thrive.

But in the case of the Chevrolet Volt range-extended electric car, with an EPA-rated electric range of 35 miles (rising to 38 miles for 2013), it turns out that at least the first 18 months' worth of buyers are logging far more miles on electricity than on gasoline.

In Volt owner groups and forums, numerous owners boast about their triple-digit gas-mileage numbers and complain that the Volt's dashboard display won't show any fuel efficiency figure higher than 250 miles per gallon. (The MyVolt.com website maxes out at 1000 mpg.)

A recent Consumer Reports post highlights data from Volt owners on its own forums: One owner has covered 7,000 miles while using just 7.3 gallons of gas (less than a single tankful), while another logged 2,800 miles on electricity out of 3,200 miles total.

As noted ad nauseam during the Volt launch in 2010, fully 78 percent of U.S. cars cover less than 40 miles a day.

The Volt's battery pack was sized around that statistic, with the vision that many or most owners would recharge overnight and might go weeks without having to fill the tank--but with a gasoline range extender to relieve them of any range anxiety related to exceeding the pack's rated range.

The Chevy Volt website has a sort of "electric odometer" showing how many miles the accumulated pool of Volts has covered on electricity, as well as total miles covered (data is gathered from cars whose owners have given permission for them to upload operating data to GM via their built-in OnStar link).

Chevrolet Volt site ticker showing total miles covered and electric miles, July 11, 2012

Chevrolet Volt site ticker showing total miles covered and electric miles, July 11, 2012

As of this morning, the tickers show a total of 95,500,000 miles covered by Volts--of which roughly 60,000,000 (or 63 percent) were driven on electricity from the grid.

Not bad for a car that some insist should be called merely a plug-in hybrid, rather than a range-extended electric car as GM would have it.

Whatever it's called, it appears that the first 15,000 or so Chevrolet Volts are being used primarily as electric cars.

Which is what Volt engineers expected and hoped for all along.


Follow GreenCarReports on Facebook and Twitter.