Under the CFP system, the Sugar takes an SEC team against a Big 12 team when the game is not hosting a semifinal matchup. The Big 12 submits its team based on its conference standings and, if needed, the tiebreaker therein, so that's why OSU is matched up against the Rebels despite being ranked lower than TCU. The SEC leaves it up to the selection committee's discretion—except when the SEC champ is available for the game, which it's not this year—and the committee picked the highest ranked SEC team available.
This is Ole Miss's ninth appearance in the Sugar Bowl, with the rest coming in the 1950s and '60s. The 1970 Sugar Bowl following the 1969 season is the last time the team played in the event. This will only be Oklahoma State's second appearance in the game, with the other being a 33-13 win over St. Mary's following the 1945 season. This will also be the third time the teams have faced each other in the postseason, with the other two coming in the Cotton Bowls following the 2003 and 2009 seasons, respectively. The Rebels are 2-0, having won the first one 31-28 and the second one 21-7.
The Rebels are one of five teams to make New Year's Six bowls both years of the CFP system, joining Alabama, Florida State, Michigan State, and Ohio State.