Over time, as engineers have developed the car's final internal layout, as per Volt lead engineer Andrew Farah, it became apparent that there really was no need to carry 12 gallons of gas.
The concept actually had two six gallon saddle-type tanks, These have been removed in exchange for a single tank at the rear. Although Mr. Farah wouldn't confirm exactly how many gallons it would contain, he said maximum range would be about 400 miles. Later, VP Jon Lauckner told me would be under 400 miles.
At this point I surmise the tank will hold between six and seven gallons, which should lead to a 340 to 390 mile total range. The tank is actually box-shaped, wider at the top than bottom. I was able to see it on the 3-D virtual reality screen (that's not it in the graphic above).
Debating how much total range is needed usually evolves into questioning how long can people hold their bladders on long trips and that fact that gas stations are particularly abundant.
We also know that some EV enthusiasts hope to never use gas at all. Thats OK, because I'm told the car will indeed run without any!
Does the maximum range really matter to you?