Las Vegas-based Allegiant Air has rolled out a roomier seat dubbed the "Giant Seat."
It represents the latest way the airline industry has created new seating options for travellers willing to pay more for extra elbow room.
In the first row and the mid-cabin emergency exit row, the six Giant Seats on the carrier's Boeing 757 offer more than 36 inches of legroom and a width of 25 inches, compared with a typical 17.5-inch width on Allegiant's economy seats. The seats are locked in a semi-reclined position.
Allegiant was required under federal rules to install such seats so crew members can rest during long flights. But when pilots and crew are not using the roomier seats, the airline is offering them to paying passengers.
Meanwhile, Southwest Airlines is coming out with its own wider seats - 17.8 inches in width - when it debuts its Boeing 737 Max jets in 2017.
"Smart airlines are starting to look at their cabins almost like retailers," said Henry Harteveldt, a travel industry analyst with Atmosphere Research Group. "Their objectives are similar to retailers as well: maximize their revenue per square foot."
In fact, nearly every major carrier has an extra-roomy version of the standard economy seat.
Virgin America offers the "Main Cabin Select." US Airways has the "ChoiceSeats." The "Economy Plus" seat is offered by United Airlines. JetBlue has the "Even More Space" seat. Delta has "Economy Comfort" seats and American Airlines has "Main Cabin Extra."
In addition to the Giant Seats, Allegiant has a new "Legroom +" seat with up to 34 inches of legroom, compared with the regular 30-inch space.
Allegiant charges about $US40 ($A42.46) to $US50 ($A53.08) more for the Giant Seats over the typical economy seat, depending on the route. The Legroom + seats are about $US6 to $US32 ($A6.37 to $A33.97) extra.