Ryanair fares to the US for under €100 - O'Leary
However, the airline chief executive admitted he probably would not initially target Irish fliers as part of the new service.
Mr O'Leary said that a Ryanair sister company operating services between Europe and the United States would sell one-way economy tickets for an average of about €90.
He said it would aim to fly between 15 major European cities and 15 major US cities.
"If we wanted to get into the pan-European transatlantic market, then starting in Dublin would be the wrong place to start. It's a tiny market," he said. "We'll need something in the order of 30-50 aircraft," said Mr O'Leary, adding that a long-haul service was at least five years away.
"We're not interested in doing something small scale."
Such fares would transform the transatlantic airline market and play havoc with carriers such as British Airways and Lufthansa.
While Mr O'Leary has previously said any Ryanair long-haul offshoot could offer €10 one-way fares, he conceded that there would only be some tickets available at that price.
Asked by the Irish Independent what the most likely average fare would be on Ryanair transatlantic routes, Mr O'Leary said he'd still be able to offer one-way tickets for under €100.
"Our average price on short-haul (flights) across Europe is €46," he said. "We'd want to have an average price in economy on a transatlantic low-cost carrier of under €100.
"The average price should be somewhere in the mid-€80s or mid-€90s."
Mr O'Leary said a low-cost transatlantic airline would be able to make profits despite selling fares at those prices.
But he said delivering such fares would depend on acquiring a long-haul fleet of aircraft at knock-down prices.
Mr O'Leary has previously signalled his desire to start a long-haul low-cost airline, but said it would probably be a stand-alone business and not directly part of Ryanair.
Mr O'Leary pointed out that Ryanair was already the biggest airline in a number of countries in Europe, including Britain, Spain, Italy and Poland.
Ryanair is due to take delivery of a new fleet of aircraft over the next few years, and Mr O'Leary is also eyeing Ryanair expansion to countries such as Egypt, Turkey, Israel and Russia.