My wife just returned from a wedding in Maine. Flew to Boston, drove up in a Volt. Took 7 gallons of gas. 6 months between fillups is possibly an exaggeration - 3 days is more like it.
I used to go for two weeks between fill-ups in a '78 Buick but that was mostly becuase it had a 24-gallon tank (and I only drove about 20 miles a day).