if your Volt has an electric range of about 40 miles and every time you leave your driveway you drive 200 miles, you'll spend most of your time running on gasoline and won't get maximum benefits from your PHEV drivetrain. But if your daily commute is within the electric range of the car, you might find yourself almost always driving on electricity alone, leading to huuuge gas savings.This seems to be what happened to Jeffrey Kaffee, the retired airline pilot who, two years ago, became the first Chevrolet Volt owner in the world. After putting 12,000 miles on his Volt, he has only burned 26.1 gallons of gasoline! That's an average of about 1.08 gallon per month. Or put another way, that's 459 miles per gallon of gasoline

459 miles per gallon of gasoline is pretty much taking it to its extreme conclusion.

What's a more normal expectation? 

 150? That's my result after 20K+ miles in the Bay Area…

150 is pretty damned good.

So you get huge gas savings -- the price differential between electricity and gas is high enough that this makes an actual monetary difference?

Or is the difference primarily psychological in nature? That you feel good by doing good?