Southwest Airlines' traffic rose 6.4 percent in August compared with last year, and the company said Wednesday that a key measure of revenue may have risen as much as 16 percent.
Passenger revenue for each seat flown one mile rose 15 percent to 16 percent during the month, the airline said. The industry pays close attention to that figure because it shows how much airlines are collecting from passengers across their entire system.
Southwest flew 7.12 billion revenue passenger miles, or one paying passenger flown one mile. That's from 6.69 billion revenue passenger miles a year earlier.
Capacity rose 3.7 percent to 8.65 billion available seat miles, from 8.34 billion a year earlier. The amount of traffic seen by Southwest rose faster than its capacity, meaning fuller planes. Load factor -- a measure of occupancy -- rose 2.1 percentage points to 82.3 percent.
For the first eight months of the year, traffic rose 2.9 percent to 51.98 billion revenue passenger miles. Capacity fell 1.8 percent to 65.57 billion available seat miles. Load factor rose 3.7 percentage points to 79.3 percent.
It may be difficult to repeat the performance this month.
Southwest has added even more capacity even as revenue data "suggests some weakness in domestic markets," wrote UBS analyst Kevin Crissey.
That means everything to Southwest because it's the only market that the Dallas airline serves.
International carriers are getting a boost from business travelers, which makes Southwest the "least favorite airline stock at the moment," Crissey wrote.
Shares of Southwest Airlines Co. rose 21 cents to $11.65 in midday trading.