Southwest Airlines Co. tweaked and trimmed its schedule on Tuesday, announcing it would eliminate 32 roundtrip flights and add 19 new ones next year.

The Dallas-based carrier released its schedule for May 9 through June 26, and it includes new nonstop service — one nonstop a day — between Denver and Tucson, Ariz.

Chairman and Chief Executive Gary Kelly said the schedule attempted to maximize the use of aircraft on the best routes.

“Our optimization exercise is a case of eliminating unproductive flights and reallocating our aircraft to match supply with demand, all the while focusing on key cities such as Denver,” Kelly said.

Among markets adding new nonstop flights in May are Nashville, Tenn., and Oakland, Calif., and Nashville and Seattle.

Southwest serves 64 U.S. cities and plans to add flights to Minneapolis in March. The airline operates more than 3,300 flights a day and carries more domestic passengers than any other.

Shares of Southwest fell 27 cents, or 3.2 percent, to $8.62 in midday trading.