Competition between airlines in the United States got even tougher on Wednesday as the third-largest carrier slashed domestic fares by as much as 50 percent.
Delta Airlines also got rid of restrictions on some fares.
Analysts say Delta's plan is intended to stem a loss of customers to discount airlines like Southwest Airlines and AirTran, which have used budget fares to lure travelers from larger carriers.
Some airline stocks dropped after the news, with investors apparently worrying that competition would force other airlines to also cut fares and revenue.
Delta and other airlines have been hurt by rising competition from low-cost carriers and rising fuel prices.
Some information for this report provided by Reuters and AP.