I used to get 14,15. Best of 17,18 if I stayed under 60mph and NEVER passed anyone. That was running 33x10.50s. Then I changed to skinny 7.50R16s. 4x4 tires from 50 years ago. I got a 5mpg bump. I now average 22mpg without thinking about it. 60-70mph in the mountains, fabulous performance. And a way smoother ride too even tho they are D Load Range.
Add in 8# lighter per tire, Rated for 60K miles, And $200 cheaper than KO2s for a set of 5.... I'll never buy anything bigger again.
I don't do any extreme off roading anymore, most of my wheeling is thru the forest and onto a beech. But there are guys running these in almost stock CJ2s on the Rubicon so it is not like I made a compromize to get a more economical tire.
I get an extra 100 miles from a tank of gas now.