$25 one way airfares

Southwest and AirTran on Tuesday launched sales featuring fares as low as $25 one way for winter, when planes otherwise could be half-empty.

Southwest is offering the lowest fares on some of its routes in 13 years. The one-way sale prices — good for travel Dec. 2-16 and again Jan. 5-Feb. 20 — are $25 on routes up to 375 miles, $50 on routes up to 549 miles, $75 on routes up to 999 miles and $100 on longer routes. The sale expires at midnight PT Thursday.

AirTran’s offer, which allows travel through Feb. 10, includes one-way prices as low as $39 on its shortest routes. Prices for longer routes range from $164 to $149 one way. The purchase deadline is Nov. 10.

The fares carry typical restrictions, including limits on the number of seats available on each flight, especially during peak-demand periods over the holidays. In most cases, they’re non-refundable.