Intense competition among airlines is making flights from Denver cheaper. A fare war is brewing, thanks to competitors including United, which has a hub in Denver, Southwest, and Frontier.

United is the world's largest airline carrier and Denver is an important market for the company, but competition from Southwest, which re-entered the Denver market in 2006 and Frontier is slashing prices.

Frontier has gone so far as offering seats on its Denver to Albuquerque route for just $9.99 each way.

No, that's not a typo -- the price is $9.99 each way.

The fare is good for travel on Tuesdays, Wednesdays and Saturdays, and amounts to just $33.98 round-trip including taxes and fees. The deal is good for flights through mid-December.

Southwest is matching Frontier, dropping its flights to $9 each way for the same Denver to Albuquerque route, but it's deep discount fare is only available Tuesdays and Wednesdays and not Saturdays.

The key is that the deal won't last long, as Frontier's special and others the airline is offering must be booked by 9:50 p.m. MDT Wednesday. A 14-day advance purchase is required and there are some blackout dates.

Southwest's deal and others must be purchased before 12:50 a.m. MDT early Tuesday morning. Travel is available through Southwest between Sept. 7 and Nov. 12.

Other cities the airlines are deeply discounting flights to in the special, centered around "Colorado Day" on Aug. 1 including Durango, Milwaukee, Salt Lake City, Tucson and Phoenix.