Southwest Airlines Co. said its traffic last month rose 3.5 percent as the number of available seats remained steady but planes were more full.
Southwest, based in Dallas, flew paying passengers 6.66 billion miles in May, compared with 6.43 billion miles in May 2009.
The airline’s number of available seats, or capacity, remained flat at 8.63 billion available seat miles.
The carrier’s load factor, or occupancy rate, rose 2.6 percentage points to 77.2 percent.
In the first five months of the year, traffic rose 1.5 percent to 30.3 billion revenue passenger miles. A revenue passenger mile measures one paying passenger flown one mile.
Capacity so far this year has declined 4.4 percent to 39.46 billion available seat miles. But as Southwest has trimmed its number of available seats, its planes have flown more full. The occupancy rate has increased 4.5 percentage points to 76.8 percent.