United Airlines and United Express added flights faster than they increased passenger traffic in April, leading to more empty seats.

The company said Friday that passengers flew 16.68 billion miles last month, a 0.4 percent increase over April 2014 despite a drop in U.S.-Europe travel.

But the company increased its passenger-carrying capacity by 2.7 percent, which airlines do by adding flights and using bigger planes. As a result, the average flight was 81.4 percent full — high by long-term industry standards, but down from 83.3 percent a year ago.

United, American and Delta recently trimmed their plans for growth due to concern about too many flights, which can lead to lower fares and thinner profit margins.

Southwest Airlines Co. has less exposure to weak international markets, and it said Thursday that April traffic jumped 8.6 percent and planes were more full.

Still, Southwest reported that a key figure — revenue for every seat flown one mile — fell 2 percent compared with April 2014. That could indicate lower average fares. United did not provide revenue information.

Shares of Chicago-based United Continental Holdings Inc. fell 8 cents Friday to close at $62.44 and were down 7 percent for the year. Share of Dallas-based Southwest rose $1.13, or 2.7 percent, to $43.23. They have gained 2 percent in 2015.

Photo Credit: The new p.s. configuration Economy Plus seats on United. United Airlines