Southwest is offering a low-fare sale with one-way flights starting at $49 for several flights.

The sale began Tuesday to celebrate the airline's 48th birthday and ends on June 20 at 11:59 p.m. Pacific Time. Tickets are valid for flights in the continental U.S. and between islands in Hawaii between Sept. 3 and Dec. 18. International flights are also available between Sept. 3 and December 11. 

The sale includes some restrictions. Some blackout dates apply for flights in the continental U.S. in November around Thanksgiving. The sale also does not cover flights between mainland U.S. and Hawaii. 

Other fares in the sale include Los Angeles to Portland (and vice versa) for $77. More expensive flights include flights from Dallas to Cancun, Mexico, for $208.

Costomers can view Southwest's fares for each city on their website.