With my new truck, I was expecting to get about 8 miles per gallon. I drove it around over 100 miles today, and the on-board computer showed me getting 12.5 miles per gallon overall. Definitely not great mileage, but better than I was expecting.
One nice thing about it is my Toyota Tacoma has a 17 gallon tank and got 16 miles per gallon (272 miles between gas station visits). The H2 has a 32 gallon tank, so 12.5 miles per gallon works out to exactly 400 miles per tank. So the slightly higher fuel costs is offset by saving my time of going to the gas station.