Ryanair will extend its reserved seating option from four to six rows, effective 1 November, with the addition of rows 5 and 15 to the paid-for ancillary service.
For a fee of between £10-15 ($16-24), passengers can reserve their seats and benefit from priority boarding on Ryanair flights.
The low-cost carrier rolled out the service in January 2012 following a trial period on selected routes.
Rival EasyJet has also been trialling allocated seating on a tiered fee structure, charging £12 for front-row and over-wing seats; £8 for the first four rows behind the front row; and £3 for any other location.
The Luton-based carrier plans to roll out allocated seating across its network this month.
Low-cost carriers have traditionally avoided giving passengers the option of reserving seats as some studies have indicated that the facility slows down turnaround times.