You can fly between March 9 and August 4, which includes half of the summer. The deadline for purchase is Thursday, March 15, or at least a week before departure. There are a few blackout dates, so go to Southwest's Web site for more information.
Booking is only online.
Delta's sale is a cookie-cutter version of Southwest's. All travel must be completed by August 4, and the purchase deadline is Thursday, March 15. Fifty-four cities are included in the savings. A list of them, plus restrictions, are posted on Delta's Web site . It is also Web-only.