Ryanair declined to comment in June when Reuters reported the Irish airline was in talks with Boeing about buying the new plane, which seats up to 230 passengers compared to 189 seats on its current 737-800 fleet and the 196 seats on Boeing MAX 200 aircraft it has ordered.
"We have told them to go back and if they can come up with a price on the Max 10 that meaningfully reduces our unit cost, we would be very happy to place an order," O'Leary told analysts on a conference call following publication of the group's latest quarterly earnings.
"We are very interested in the aircraft - but we are only interested in this aircraft or any aircraft if it lowers our unit costs," he said. "We do believe that a 230 seat aircraft can deliver a meaningful reduction in unit costs."
O'Leary said Ryanair did not need to order any more planes for five years, but would consider an offer if the price was right.
Boeing in June launched what would become the largest version of its 737 MAX medium-haul family, designed to challenge the popular Airbus A321 flown by Ryanair rivals.
Rivals easyJet and Wizz have ordered A321 planes, which seat up to 239 passengers as they seek to keep costs per seat under control by shifting to slightly bigger planes.
Ryanair on Monday reported profit after tax up 55 percent in the three months to end-June, but triggered a share sell-off after it warned it might cut fares in late summer by as much as 9 percent from last year.
(Conor Humphries - Reuters)