Southwest Airlines Company launched a fare sale on Tuesday for travel this winter, and rival airlines began matching the prices on many routes.
Southwest said it was offering round trips starting at US$98 for flights under 500 miles each way, with longer round trips costing up to US$298.
It said that the prices were good until midnight Thursday night and also applied to its AirTran Airways subsidiary.
The company said that sale prices applied to a limited number of seats, covered only nonstop flights, weren't available on Fridays or Sundays, and carried other restrictions.
The offer covers travel between December 4 and December 18, and again between January 7 and February 12.
By Tuesday afternoon, United, Delta, American and US Airways began offering similar prices and restrictions on most domestic routes that they share with Southwest, according to Rick Seaney, CEO of fare-tracking website FareCompare.com.
Separately, Travelocity.com said Tuesday that the average domestic airfare for Thanksgiving travel was US$415 including taxes, an increase of seven per cent from last year.
The online travel agency said many popular routes were cheaper than US$415, however. It advised travellers to book flights before November 10, when it expects fares to start rising sharply.