Allegiant Air is now offering "Giant Seats" on select flights. The airline has added extra large seats to some economy rows on Boeing 757 planes that make long-haul flight to the Hawaiian cities of Honolulu and Maui and some cities in the western U.S.

The seats are much bigger than usual airline seats. They are 25 inches wide while standard seats are 17.5 inches. The seats have only been offered for purchase over the past few weeks, but already seem to be a success, Yahoo reports.

"Generally we're seeing people purchase them, so there is a demand for them," Allegiant Air spokesperson Jessica Wheeler told Yahoo.

The addition is wider seats is part of the FAA's rule that require wide seats for crew members that must rest on longer flights. However besides the seats for crew members, the airline also thought that customers might be willing to pay more for a roomier seat on a long flight.

The seats can be reserved by passengers on some flights to Hawaii and Las Vegas. The Giant Seats come at a fee of course. They are available on all six of Allegiant's 757s which can fly longer distances.

Passengers can also opt to have extra legroom on the flights.  There is a "Legroom+" option which allows travelers to choose seats with six extra inches of space, bringing it to a total of 34 inches of legroom between the seats in front.

Of course adding bigger seats and more legroom comes with a catch for the airline. The planes now have fewer seats to make room for the new seating so the planes have 215 seats instead of 223.

The seats also come with a fee. The cost of a Giant Seat on Allegiant Air will cost about $40 to $50 more than a standard seat.

Allegiant Air isn't the only airline offering roomier seat options. Virgin America also has seats with six extra inches of legroom. United offers extra legroom with its "economy plus" option.  JetBlue has always boasted extra legroom with up to 38 extra inches. US Airways gives passengers the option of having "Choice Seats' which include choosing from aisle or window seats and some exit rows near the front of the plane. The seats aren't bigger but it gives passengers the ability to board and exit the plane before most passengers.