TAM Airlines and US Airways have today completed their transition to Oneworld alliance.
Both carriers started offering Oneworld services and benefits from their first flights this morning.
The transfers are the largest single-day expansion for the airline alliance since its inception 15 years ago.
As a result, Oneworld now has just under 100 new destinations in its network, almost a 10 per cent increase.
Annual seat capacity has been expanded by 20 per cent, and passenger traffic has been boosted by nearly a third, adding approximately 120 million customers each year.
Oneworld governing board chairman, and IAG chief executive, Willie Walsh said: "By adding TAM Airlines and US Airways, Oneworld will consolidate its leading role within Latin America and on flights between the region and both the United States and Europe.
“We already have strong and long-standing relationships with the American Airlines and LATAM Airlines groups. These two new partners bring outstanding quality and scale to the alliance, further strengthening its position as the best option for frequent international travellers"