You can almost set your watch by airline sales, these days. Once again, Southwest Airlines launched a Monday afternoon fare sale which by midnight American, United, Continental, Delta, AirTran, and US Airways had matched.
This week’s sale is valid for travel through May 25th, with a 14 day advance purchase required. The best fares are available for Monday through Thursday travel; weekends including Fridays are slightly more expensive.
The sale ends at midnight this Thursday.