The airlines offered another 10percentt discount for fares purchased through their Web sites.
The second column is for fares purchased inside of 14 days.
Monthly, semimonthly, and even daily passes are sold on many systems, which keeps fare purchase off the vehicle and makes the process of checking for prepayment fast.
Among current Air France promotions are a half-price fare for a companion with a full-fare purchase, based on availability, and a one-way fare of $4,254, about 18percentt less than the usual $5,202, available with a purchase at least four days before departure.
Update: United's Web site now says the airline will charge a $150 "administrative fee" to change your ticket to a lower fare for purchases made on or after March 20.
Travelers will also be able to use mileage for one-way fares (half the round trip fare) and purchase tickets with a combination of points and cash.
All these fares are for purchase over the Web (www.aa.com); add $5 for buying over the telephone and $10 at the airport.
The air fares are for purchase 7 to 21 days in advance.
Airlines acknowledge that the Saturday-night-stay requirement for cheaper advance purchase fares was conceived to discourage business travelers from flying at the discounts that leisure travelers routinely expect.
Last year, average fares for tickets purchased less than a week before travel were about $2,600, almost double the price of those bought at least 28 days in advance.
