I had gone 2.5 months and 3900 miles since my last fill-up, but had to take a long trip today (140 miles). Just for grins, I ran the Volt out of gas on purpose. I put it in mountain mode, and just drove it until the engine died and the car switched back to electric with 14 miles range. I drove until I had 4 miles left and then filled up. The most interesting thing about the experience is that the trip odometer said I had used 9.6 gallons, and I put 9.753 gallons in the car. Pretty good for a 9.3 gallon tank! I'm still impressed with the highway mpg in gas mode. 40.9 MPG average at 67mph.