As others have pointed out, the fire marshall caps the attendance at seats sold with an official seating capacity at 102,455. Prior to that change in policy, the "largest" crowd to see a Vols game was 109,061 for Florida in 2004. At that time, Neyland's official seating capacity was 104,079.
With several minor adjustments relative to phasing of improvements, the current official seating capacity is 102,455. The 102,455 includes the number of seats in the executive suites. I would imagine that counting those who bought seats and who end up not going for whatever reasons compared to all the other persons not counted because they are players, coaches, service persons in the stadium, police, etc., the crowd likely will exceed 102,455.
Everyone cites the last biggest OC game at Neyland where the Vols was ranked as being Cal 2006. The Cal game attendance in 2006 was 106,009 when the official seating capacity was 102,037. Tennessee was ranked #23 for that game and Oklahoma was #12 or #9 depending upon the poll.