DUBLIN (Bloomberg) — Ryanair Holdings Plc chief executive officer Michael O’Leary plans to start a discount trans-Atlantic airline, offering fares as low as $12, following the “open skies” accord between the US and European Union.The new airline would fly from Ryanair’s existing bases including London Stansted, Dublin and Frankfurt-Hahn, O’Leary said yesterday in a briefing to reporters. The carrier would go to secondary US airports at destinations including New York, San Francisco, San Diego, Boston, Dallas and Florida.

The agreement to open up the market for trans-Atlantic flights will make the new airline possible, O’Leary said. The new carrier would compete against network airlines including British Airways Plc and Virgin Atlantic Airways on lucrative trans-Atlantic routes.

“Ryanair’s business model to date has been superb but this could be a bridge too far,” said David Buik, an analyst at BGC Partners in London. “He may well have to reconsider starting an airline in a market that’s already incredibly competitive.”

Shares of Ryanair, Europe’s largest discount airline, fell 5 cents, or 0.8 percent, to 6.01 euros in Dublin. The stock has risen 66 percent in the past 12 months, boosting the carrier’s market value to 9.3 billion euros.

Ryanair has grown from a single airplane in 1985 to a fleet of 133 flying to 130 European destinations. The Dublin-based airline is now the third-biggest in the world in terms of market value and competes with network carriers on short-haul routes.

Ryanair’s entry into the European market, as well as that of its biggest discount competitor, EasyJet Plc, triggered a price war among European airlines in the late 1990s.

Ryanair charges what it claims to be the lowest fares in Europe, with routes such as London to Barcelona regularly selling for as low as 1 penny, excluding taxes. Tickets on the new trans-Atlantic service will cost from 10 euros, O’Leary told reporters. The carrier will offer premium seats in addition to “no-frills” economy. Discount airlines such as Ryanair and EasyJet have doubled their capacity in the past four years, leading network carriers to respond by focusing on attracting business- and first-class passengers.

“Consumers want frills included on long-haul flights, not ‘no-frills’,” said Paul Charles, a Virgin Atlantic spokesman. “Opening up markets breeds fresh competition and new ideas, which really benefit consumers.”

British Airways, Europe’s third-biggest carrier, welcomed competition on all routes to the US. “We are a full-service airline offering a world-leading product onboard and exceptional customer service,” Thomas Coops, a spokesman, said. British Airways shares rose 10.5 pence, or 2.1 percent, to 514 pence in London.

The new service will also compete with Aer Lingus Group Plc, the Irish carrier that O’Leary tried to buy in October. Ryanair’s hostile takeover bid has lapsed since being referred to the European Commission on concern the combination might harm competition on Irish flights.

“What O’Leary wants to do is bring Aer Lingus back to the table,” said Buik. “For Aer Lingus, being a relatively small carrier, to have somebody on your doorstep say that they’re planning to fly people across the Atlantic for 12 bucks is quite damaging.”

Shares of Aer Lingus fell 8 cents, or 2.5 percent, to 3.14 euros in Dublin.

Aer Lingus said March 22 that it will use the open-skies accord to add three long-haul routes, to Washington Dulles, Orlando, Florida, and San Francisco, to its Dublin-based network by the end of 2007. The airline had been restricted to four US cities under an Ireland-US agreement to be replaced by the EU accord.

The new agreement, which takes effect in March 2008, allows EU airlines to fly to the US from any of the bloc’s airports, instead of just their home countries. It also opens London’s Heathrow airport to more carriers, ending the lock Virgin Atlantic, British Airways and two US companies have on trans- Atlantic flights to and from Europe’s busiest airport.

Funding for the new carrier, which O’Leary said will start in three or four years, will come from a “private placement,” not from Ryanair. O’Leary estimated the start-up cost to be 100 million euros to 200 million euros.

“There’s lots of investors who are keen to see a long-haul low-fare trans-Atlantic service,” O’Leary said on a flight from Dublin to Frankfurt. “Money is the least thing we need.”

The airline, which would have its own name, may buy as many as 50 aircraft, probably Boeing Co. 787s or Airbus SAS A350s. It will have its own board of directors and be a “sister” or “associate” company to Ryanair, O’Leary said.

O’Leary will have “some say in the way it is run,” he told the reporters. “It might be something I do when I step down from Ryanair.” He has said he will resign from Ryanair in the next two or three years. O’Leary said he will “probably” not be the new carrier’s CEO.

Ryanair operates short-haul flights that allow it to land a plane, disembark its passengers, board another set of travellers and take off in 25 minutes. The carrier’s “fast turnaround time is crucial” as it allows planes to do more flights and keeps costs low, Ryanair says on its web-site.

Low-cost trans-Atlantic flights were attempted once before, by Freddie Laker, a British entrepreneur. He set up Laker Airways in 1966 to fly “Skytrain” services between New York and London. The carrier went bankrupt in 1982 after struggling to keep load factors, or the proportion of seats filled, high enough to offset costs during quieter travel periods.