Here is one possibility.
TCU wins out.
Baylor has a loss to TCU but beats OU AND OSU.
OSU beats OU, loses to Baylor.
That gives three teams an 8-1 record, and they are 1-1 against each other, so they would have to go to additional tie breakers.
As best I can figure it there is no possible three way tie involving Oklahoma, unless you start looking at three teams being 7-2.