British Airways, American Airlines and Iberia have been given the go-ahead by US authorities to operate joint transatlantic services.
The US Department of Transportation has granted anti-trust immunity for the alliance following European Union approval last week.
As part of the green light, the three airlines will have to give up an unspecified number of take off and landing slots at Heathrow to rivals.
The carriers plan to launch the transatlantic joint business this autumn and will co-operate commercially on flights between the EU, Switzerland and Norway and the US, Canada and Mexico.
Passengers will be able to travel more easily on all three airlines’ combined route network that will serve 433 destinations in 105 countries with 5,178 daily departures.
By working together, the three will expand customer choice by supporting routes that would not be economically viable for a single airline, they claim.
Passengers will have greater access to discounted fares, expanded opportunities to earn and redeem frequent flyer miles and elite tier benefits on flights and continued reciprocal airport lounge access.
BA chief executive Willie Walsh said: “This final approval is fantastic news for all three airlines and the oneworld alliance.
“We’ve waited 14 years to bring the benefits of the transatlantic joint business to our customers and level the playing field with the other two global alliances.
“As we have argued all along, the EU-US market is highly competitive and Heathrow’s liberalisation in 2008 opened it up even further. We are delighted that the US and EU authorities have recognised this.”
He added: “We’re pleased that the DOT and EU have worked together to ensure that there is consistency in the number of slots that the three airlines have to give up for our competitors to use on services from Heathrow to the US.”
American Airlines chief executive Gerard Arpey said: “We look forward to delivering enhanced competition for customers on transatlantic flights.
“By working collaboratively, we will enhance our product offerings, strengthen our route networks and better position our airlines to compete in an ever-changing global aviation marketplace.”
Iberia executive chairman Antonio Vazquez said: “A new kind of collaboration between our three airlines will lead to better service levels for our customers.
“I am convinced that consolidation is the best and only way to succeed in the airline industry, and the approval we have received today to create a joint business is a very important step towards this consolidation process.”
However, Virgin Atlantic boss Sir Richard Branson warned of a ‘monster monopoly’ being created, claiming that BA and AA would “stifle competition, raise prices and reduce choice”.
Fellow oneworld members Finnair and Royal Jordanian also received antitrust immunity from the US DoT.