If the following two things happen:
Big 12 South winner (Oklahoma, Texas or Texas Tech) is upset by Missouri in the Big 12 championship game
Oregon State beats Oregon or USC loses to UCLA (Oregon State wins Pac 10)
then the BCS National Championship Game will be
the SEC Championship Game winner (Florida/Alabama) vs. Utah.
Big 12 South winner (Oklahoma, Texas or Texas Tech) is upset by Missouri in the Big 12 championship game
Oregon State beats Oregon or USC loses to UCLA (Oregon State wins Pac 10)
then the BCS National Championship Game will be
the SEC Championship Game winner (Florida/Alabama) vs. Utah.