The 2005 season marks only the eighth time in 50 years that exactly two teams have gone into the bowl season undefeated. This has been a major criticism of the BCS format, which does not use a playoff to determine the national championship. Unless there are exactly two unbeaten teams, both from BCS conferences, the choice of the top two teams can generate controversy. If more than two undefeated teams remain, then one or more of those teams must be left out. If one or fewer undefeated teams remain, then an opponent must be chosen from among the one-loss teams, meaning that other one-loss teams will be left out.