Texas 05, Boise State 06, Utah 08, Boise State and Alabama 09, TCU 10, Ohio State 12 and Florida State 13
Given 128 FBS teams that means that there have been 8 undefeated seasons out of the last 1152 FBS seasons.
So the odds of "one single season" is 0.69% or about once every 144 seasons.
Given those odds, having our last undefeated season 30 years ago means that we are *WAY* ahead of the average.
Greg