I looked up basically all of the major historical rivalries I could think of. It looks like Kansas-Oklahoma is the winner with 13. There could be more obscure rivalries that played more but I'm not researching that. Somebody get Mike Waters to address this in his mailbox! Interestingly, Kansas and Oklahoma have only played one OT game since the late 1970s so we're catching up. I was actually surprised by how many big rivalries had only a couple of OT games in their history.