Normal Tahoe is 13 city and 17 Highway, combined 14
http://www.fueleconomy.gov/feg/noframes/22636.shtml
They are claiming 20 city and 21 highway for the hybrid, combined 20.5?
15k miles a year that is over $1,000 savings a year at $3 a gallon
(If you want the math I can post that as well)