As a result, it is impossible for a consumer to know how many discount seats will ultimately be sold on any given flight.

Of course, calling soon after an ad appears improves your chances of finding a discount seat.

A major question is how the fare restructuring will affect the number of discount seats available on any flight.

The carriers do not disclose the number of discount seats available.

"If you want one Saturday morning, there'll be plenty, and late Saturday, there's probably nothing but discount seats."

Even before the Eastern strike tightened the supply of discount seats, yield management systems had begun to trim their number.

A spokesman for American said the airline had not reduced the number of discount seats.

"They really can't afford to be holding discount seats and then have the passenger back out."

For example, under normal circumstances the system automatically limits the number of discount seats on heavily traveled routes.

A few minutes later came a similar offer peddling discount first-class seats for another otherwise overbooked flight.