Ryanair is reportedly in advanced negotiations to purchase some 100 Boeing 737 MAX aircraft, fitted with extra seats, in a likely $10bn deal that could be sealed in days or weeks.
A deal for about 100 of the jets could be inked as soon as mid-September, Reuters reported.
The budget carrier needs the planes to boost traffic to 120 million passengers per year by 2022, from just over 80 million at present.
Pursued by the news agency, the Irish firm did not comment.
America's Boeing and European rival Airbus are adding seats to tempt low-cost carriers. Flying aircraft with more seats pushes down the operating costs per seat, the key driver of aircraft economics.
"The 200-seat version [of the 737 MAX] is almost tailor-made for Ryanair," Stephen Furlong, an analyst with Davy Stockbrokers in Dublin, told Reuters.
"In addition to the fuel efficiency, the extra seats should give them an extra 5% unit cost savings.
"Ryanair are a massive customer for Boeing, so they will clearly treat them well. If you were Boeing and you lost Ryanair, that would be huge. There is dependence, but its mutual," Furlong added.
Ryanair, in July, increased its profit forecast for 2014 after a hugely successful first quarter.
The first three months of the year saw the airline increase its profits by 152%, on an annual basis.
The main reason behind the rise was this year's early Easter, with traffic growing to 24.3 million and revenues up 11%.