I think we need more info into the specs of your sport. What model is it? Whats the engine size? 2wd or 4wd? Recent tune-up? Tire size? City, Highway, mixed driving? Based on my own sport ('03 xls - full time 4wd) with slightly larger than stock tires I'm getting 15-16 mpg in the city and 18-20 on the highway.

'88 Raider 2.6L - SW Hubs, Weber 32/36, Off-road Pkg - Dead
'88 Monty 2.7L - 5" Lift, Weber 38, 33's, Dual Fans, Dual bouncy (more goodies to install) - Still Kicking.
'03 Monty Sport - XLS, BFG A/T's - Dead