HOUSTON (AP) –  Southwest Airlines is planning to offer international service out of Houston’s Hobby Airport with the city council’s adoption of a $100 million plan to expand the airport and add international flights.

Southwest, the nation’s fourth-largest airline by passenger traffic, plans to begin the service in 2015.

The airline already runs more than 130 daily flights from Hobby, making it Southwest’s sixth-busiest airport. It plans to add about 20 more.

Although Southwest doesn’t fly beyond U.S. borders, its AirTran Airways subsidiary does, and Dallas-based Southwest plans to fold AirTran into the Southwest brand over the next several years.

AirTran now flies to Mexico and the Caribbean from cities including Atlanta, Baltimore and Los Angeles.

(Copyright 2012 by The Associated Press.  All Rights Reserved.)