DALLAS >> American Airlines expects to add more seats to some of its planes, which could mean less leg room for passengers.

The airline’s parent company, AMR Corp., disclosed the move in a regulatory filing Wednesday.

American’s vice president of flight service, Lauri Curtis, said that the airline constantly examines its operations, including trying to match the number of seats with travel demand.

Curtis said airline officials expect to add seats on Boeing 737 and McDonnell Douglas MD-80 jets, "but we haven’t yet determined the right number of seats, and as a result, the impact on revenue and cost."

Airlines add seats for the obvious reason — they can sell more tickets that way. But it usually results in less leg room for passengers.

Southwest Airlines Co. has been installing thinner seat cushions but is still cutting an inch of leg room as it adds six seats each to some of its Boeing 737s. The makeover will help Southwest boost passenger-carrying capacity by 4 percent without buying any new planes.

American spokeswoman Stacey Frantz said that whatever American decides, it will still sell what it calls Main Cabin Extra seats, which have more leg room and cost more than other seats in economy class.

While raising revenue, adding seats can also increase an airline’s labor costs.

Frantz said American’s 737s have 148 or 150 seats. Federal safety rules require one flight attendant for every 50 seats, so exceeding 150 seats would force American to put a fourth flight attendant on those planes.

American operates 195 Boeing 737s and 190 of the MD-80s, according to its website. Together, the planes make up nearly two-thirds of American’s fleet.

American’s employees got an update on the seating plans during a meeting in Fort Worth, Texas, with executives who’ll lead the airline after it merges with US Airways Group Inc.