Irish low-cost airline Ryanair is in advanced talks to buy at least 100 Boeing 737 MAX jetliners with extra seats in a potential $10 billion deal that could be finalised in days or weeks, sources said.

The move comes two months after Boeing said it was studying plans to offer more seating in its uper centoming 737 MAX by introducing a version with 200 seats, 11 more than the current maximum.

A deal for about 100 of those aircraft could be reached as early as the middle of September, a source in the know said.

'Ryanair does not comment upon, or engage in, rumour or speculation,' a spokesman for the airline said. A European spokesman for Boeing declined to comment.

A new order from Europe's biggest no-frills carrier would mark a new phase in efforts by Boeing and European rival Airbus to appeal to ultra-low cost carriers.

'The 200-seat version is almost tailor made for Ryanair,' said Stephen Furlong, an analyst with Davy Stockbrokers in Dublin. 'In addition to the fuel efficiency, the extra seats should give them an extra five per cent unit cost savings.'

Keeping up demand for the most popular types of airliner has become the Holy Grail for both planemakers as they embark on ambitious production plans, with higher output volumes playing an important role in cutting costs and boosting margins.

In June, Airbus said it would increase the maximum number of seats on its revamped A320neo to 189, matching the capacity limit on the main variant of the Boeing 737 MAX and providing fuel savings of 3.5 per cent per seat.

Weeks later, Boeing leapfrogged its rival by announcing plans to offer a 200-seat version of the 737-8 MAX, which Boeing Commercial Airplanes chief executive Ray Conner said would offer unspecified cost savings of 5per cent per seat.

An industry source said Ryanair was expected to place a large order for the modified version of the 737-8 MAX 'soon'. Ryanair had been shopping for at least 100 and possibly as many as 150 of the higher-capacity aircraft.-Reuters