I have a "goal" of 13 (commuting) for my 86 FJ60 with 32" tires and 331k miles; depending on traffic and weather it varies between 11.5 and 13.5.
Highway mileage varies a lot, too. I'm satsified with 13 on the grades of I70 and US285 west of Denver (running as fast as necessary/possible to stay out of the way) and 14.5 on the flats east of here running 65-68mph. My time all-time highway records are 16.1 between Denver and Omaha running 62mph with a howling tail wind and 16.9 (!) on the secondary roads of Chihuahua state running 45-50mph all day on the back way from Cuahtemoc to Juarez...nothing wrong with Pemex Magna grade.
The few times I've tried to accurately check off-road mileage over the years (fill up just after leaving the highway, one to four days of low-range 4-wheeling, fill up before returning to highway) has yielded between 10.4 and 11.8.
Highway mileage varies a lot, too. I'm satsified with 13 on the grades of I70 and US285 west of Denver (running as fast as necessary/possible to stay out of the way) and 14.5 on the flats east of here running 65-68mph. My time all-time highway records are 16.1 between Denver and Omaha running 62mph with a howling tail wind and 16.9 (!) on the secondary roads of Chihuahua state running 45-50mph all day on the back way from Cuahtemoc to Juarez...nothing wrong with Pemex Magna grade.
The few times I've tried to accurately check off-road mileage over the years (fill up just after leaving the highway, one to four days of low-range 4-wheeling, fill up before returning to highway) has yielded between 10.4 and 11.8.