The 2004 Jeep Grand Cherokee averages 14 miles per gallon in the city and 19 miles per gallon on the highway. It averages 16 miles per gallon when city and highway miles are combined. The gas tank holds 20.5 gallons of fuel. The annual cost to drive a 6-cylinder Cherokee for a year is estimated to be $2,288. For an 8-cylinder engine, the cost is about $2,441. These figures assume the Jeep is driven 15,000 miles per year, with 55 percent of those miles in the city and 45 percent on the highway. The formula assumes gas costs $2.44 a gallon.