DALLAS (AP) – Southwest Airlines Co. and its AirTran subsidiary launched new sales on Tuesday for travel during late summer and the typically slower fall season.

The sales were announced as an attempted fare increase led by United and Continental collapsed.

The Southwest and AirTran deals are being offered through Aug. 1, although seats are limited and not available on all flights.

The AirTran sale covers flights between July 30 and Nov. 16 for most cities, with the lowest prices on Tuesdays and Wednesdays. Some short trips, such as Atlanta to Richmond, Va., are $59 at off-hours. Peak-time flights between Milwaukee and Cancun start at $134 each way, the airline said.

Southwest's sale also starts at $59 each way for some short trips, and covers travel from Aug. 23 to Dec. 14 except Fridays and Sundays. There are 18 blackout dates around Labor Day and Thanksgiving.

Airline pricing is complicated and constantly changing, and sales aren't always what they appear.

In Southwest's case, the lowest sale prices are $35 to $50 cheaper each way than some Houston-Denver and Houston-Los Angeles flights the day before the sale takes effect.

But on some Chicago-Boston and Chicago-Denver flights, Southwest's website showed available fares one day and one week before the sale starts that were $24 to $52 less than the advertised special rate that begins Aug. 23.

The sales were announced a day after an effort by United and Continental to raise fares on many U.S. routes by $4 to $10 per round trip collapsed. The price hike seemed to be sticking over the weekend but crumbled after Southwest, which raised some prices, and American Airlines first matched, then rescinded the higher fares.

Rick Seaney, CEO of FareCompare.com, said all the airlines rolled back their increases by late Monday night. He said after Southwest only partially matched the increase and American retreated on Monday, "the hike was doomed."

Airlines want to raise prices to offset high and volatile jet fuel costs, but the strong growth in travel demand earlier this year has slowed as fares rose and the economy remained sluggish. Traffic declined in June at United, Continental and Delta, compared with June 2010.

Seaney said he expects United to continue attempts to raise prices over the next few weeks.

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