Unit revenues at Southwest Airlines and its subsidiary AirTran Airways stayed flat in December 2012.
Passenger traffic declined 0.2% during the month, and capacity grew 0.2%, resulting in a 0.4 percentage point decrease in load factor to 78%.
Southwest's revenue passenger numbers fell 3.7% to 8.61 million passengers during the month.
On a full-year basis, passenger traffic fell 1% and capacity declined 0.3%. The passenger load factor fell 0.5 percentage point to 80.3%. Passenger numbers declined 0.7% to 109 million.