Ben Mutzabaugh

USA TODAY

Southwest rolled out a fare sale this morning (Oct. 14) in which the price of its flights appear to be based on distance. The sale covers flights in early December and from Jan. 6 through mid-February.

Southwest in the past has rolled out fare sales in which fares were pegged to mileage thresholds. For example, Southwest rolled out a sale around this date last year in which flights of 500 miles or less costs $49 each way and increased from there. Flights of 501 to 1,000 miles cost $99 each way and flights of 1,001 to 1,500 miles cost $129 each way. Flights of more than 1,500 miles went for $149 each way.

Southwest says that's not the case this time around, with spokeswoman Thais Conway telling Today in the Sky that "we're not advertising this as a mileage-based sale."

Still, this Southwest sale appears to closely mimic its previous distance-based promotions. Even the carrier's four sale fares — $49, $99, $129 and $149 each way — match the fares it offered on its distance-based sales of years past.

Whatever the details, travelers can snag advertised round-trip fares as low as $98 on short routes. Many routes, such as Chicago-Minneapolis and Atlanta-Richmond, Va., showed fares as low as $96.20 (including taxes), with Southwest apparently rounding up the fares in its sale ads. Fares on longer flights appear to increase incrementally more in a a rough correlation with the distance flown.

Regardless of the fare and distance, deal-seekers will have to act fast to lock in those prices. Southwest's sale runs only through the end of the day Thursday (Oct. 16).

United, Virgin American and JetBlue were among the airlines matching Southwest's fares on some but not all routes as of 11:40 a.m. ET Tuesday.

As for Southwest, its sale fares are good for flights in early December and for the first few weeks following the New Year's holiday. Those periods tend to be two of the slowest periods of the year for U.S. airlines. The sale fares are blacked out on flights from Dec. 18 through Jan. 6, a period when demand spikes around the Christmas and New Year holidays.

Southwest's sale prices also are offered on the few routes still flown by subsidiary AirTran.

With most shorter routes available at just $49 each way, that makes for round-trip fares of less than $100 on dozens of Southwest and AirTran city pairs.

Among the dozens of sub-$100 options: Atlanta-Richmond, Va.; Austin-New Orleans; Baltimore-Albany, N.Y.; Boston-Baltimore; Buffalo-Baltimore; Chicago Midway-Des Moines; Dallas Love-Amarillo, Texas; Denver-Salt Lake City; Detroit-St. Louis; Grand Rapids, Mich.-St. Louis; Kansas City-Chicago Midway; Los Angeles-Tucson; Minneapolis/St. Paul-Chicago Midway; New York LaGuardia-Akron/Canton, Ohio; Oakland-Orange County, Calif.; Phoenix-Albuquerque; Portland, Ore.-Sacramento; and San Francisco-Las Vegas.

As for the fine print, the sale covers nonstop flights from Dec. 3 through Dec. 17 and from Jan. 6 through Feb. 11. All Friday and Sunday flights are excluded. Additional days are excluded from the sale on flights to Florida, Nevada and Puerto Rico. The cheapest sale fares will disappear from flights on all routes as those fares begin to sell out.

Tickets must be purchased Thursday by 11:59 p.m. in the time zone of the originating city.