Southwest Airlines and AirTran Airways will launch non-stop flights on five new routes from 12 August.
Southwest will begin thrice daily flights between Atlanta and Norfolk and thrice daily flights between Atlanta and Louisville. It will also launch twice daily flights between New York LaGuardia and St Louis and twice daily flights between San Antonio and St Louis.
In addition, AirTran will start twice daily flights between Akron-Canton, Ohio and Chicago Midway.
Southwest closed on its acquisition of AirTran in May 2011.
AirTran will be the only carrier operating between Akron-Canton and Chicago Midway, schedules in Innovata show.
Southwest will compete against Delta Air Lines on Atlanta-Norfolk, Atlanta-Louisville and New York LaGuardia-St Louis. Vision Airlines also operates between Atlanta and Louisville and American Airlines flies between New York LaGuardia and St Louis.
Southwest currently operates one-stop service on New York LaGuardia-St Louis and San Antonio-St Louis. No airline currently flies non-stop between San Antonio and St Louis.