The Big 12 is tied with the SEC for most appearances in the game (7; four by Oklahoma, two by Texas, and Nebraska got in in 2001 even though they were shitty) but they are 2-5 compared to the SEC's 6-0.
SEC: 7 apps, 6-0
Big 12: 7 apps, 2-5
ACC: 4 apps, 1-3
Big 10: 3 apps, 1-2
Pac 10: 3 apps, 1-1
Big East: 2 apps, 1-1