Conversation so far:
who's ranked number one in the big 12
The Oklahoma Sooners were ranked no. 1 in the Big 12 Football Standings 2019
who is the athletic director of the university of oklahoma
The University of Oklahoma's current athletic director is Joe Castiglione
who is the oklahoma sooners' football coach
Lincoln Riley is currently the head football coach at the University of Oklahoma.
when did the oklahoma sooners start participating in college football
The Sooners have been participating in college football since 1895

Question: how many national championships has the team won
Self-contained rewrite: how many national football championships have the oklahoma sooners won