The company said that passenger revenue for every seat flown one mile increased about 4 percent last month compared with July 2013. That is a closely watched figure in the airline business; it rises when airlines fill more seats or charge higher average fares.
The comment from Southwest, following a 3 percent increase in the same revenue figure at Delta Air Lines, show just how airlines are benefiting by limiting new flights to keep planes full at modestly higher fares.
Passengers flew about 10.63 billion miles last month on Southwest and AirTran, up from 9.98 billion in July 2013. That growth outstripped a 2.6 percent increase in passenger-carrying capacity, so the average flight was 86.7 percent full compared with 83.5 percent in July 2013.
Shares of Dallas-based Southwest rose 9 cents to $28.21 in afternoon trading. They began the day up 49 percent in 2014.