20-0 is possible. 19-0 can be beat if somehow there are three 16-0 teams in one conference and the lowest seeded one wins four playoff games. While it is unlikely, there can be a 20-0. 16-0 can't be beat unless they extend the season to more regular season games. Come to think of it, that scenario is much more likely than 20-0. I've always wanted to start a pointless thread.