Passenger traffic at JetBlue (JBLU)  is growing, but a key revenue figure is rising more slowly than at some bigger competitors.

JetBlue Airways Corp. said Tuesday that traffic rose 4.3 percent last month compared with July 2013, as passengers flew 3.JEt 67 billion miles.

The airline increased capacity by 3.5 percent. Airlines usually boost capacity by adding flights or using bigger planes that hold more passengers. The average flight in July was 88.3 percent full, up from 87.6 percent a year earlier.

JetBlue said passenger revenue for every seat flown one mile rose about 1 percent from July 2013. That's a closely watched statistic in the airline business, and it rises when airlines fill more seats and boost average fares.

Southwest Airlines reported a 4 percent July increase in the same figure, and Delta Air Lines posted a 3 percent gain. American and United did not provide a revenue figure for July.

JetBlue shares have rallied sharply since late April, which analysts attribute to speculation that CEO Dave Barger will be replaced by the airline's president, Robin Hayes. Barger's contract expires in February.

Stifel analyst Joseph DeNardi said investors increasingly believe that Hayes would impose a fee on a passenger's first checked bag and add seats to planes. DeNardi said, however, he isn't sure that Hayes would take either step.

Imperial Capital analyst Bob McAdoo said last week that JetBlue will face growing pressure to make changes, which he suggested could include dropping or fixing money-losing routes, adding seats to its Airbus jets and adding a fee for the first checked bag.

JetBlue operates about 850 flights a day in the United States, Latin America and the Caribbean, with key markets in New York, Boston and Fort Lauderdale, Florida.

Shares of the New York airline fell 11 cents to $11.63 in afternoon trading. They began the day up 37 percent in 2014.