It is the latest moved in a continuing a trend among airlines to bolster revenue with creative fees on perks that used to be included in the ticket price.
The carrier said the program called "Express Seats" lets passengers pay to sit in those seats and enter the plane in the first group, to speed boarding and exiting.
The fee starts at $19 for short flights like St. Louis to Chicago and rises to $39 for longer trips like Chicago to Honolulu. The program applies to travel within the United States, including Puerto Rico and the US Virgin Islands.
Customers may purchase the seats only at airport self-service check-in machines any time from 24 hours to 50 minutes before departure.
Cash-strapped airlines have been tapping into new ancillary revenue streams to offset historically low ticket prices and volatile fuel costs. Some of the more controversial fees, like one to check a single bag, has been broadly accepted by the US airline industry.
Airlines also have experimented with fees to sit in exit rows and in aisle seats.
