British Airways and Iberia's joint venture with American Airlines has been extended to include AA's merger partner US Airways.
US Airways joined the Oneworld alliance on March 31, immediately following its exit from Star Alliance the day before (see news, April 1).
As a result, passengers booking with BA and Iberia can now select from 70 direct flights a day between the UK and US and 16 flights a day between Spain and North America.
The joint business venture includes all scheduled flights operated by Oneworld alliance members American and US Airways, BA, Iberia and Finnair between North America and Europe.
The deal is a revenue sharing agreement under which member airlines have permission to co-ordinate schedules and pricing on North Atlantic routes.
Doug Parker, AA's CEO, said: "Bringing US Airways into the joint business network is an important step for us as we continue to advance our collaboration with alliance partners to increase growth, market share and competition.
"Joining our entire merged company into this agreement creates a stronger and more competitive joint business, and will provide faster and easier connections for customers on hundreds of flights between North America and Europe."
US Airways brings 28 transatlantic routes into the joint business, of which 27 are new, and gives BA and Iberia customers access to more than 50 additional destinations in North America.
The venture also provides up to 17 flights a day between London and New York.
IAG claims the partnership will bring benefits including more attractive corporate programmes, increased flights, premium seats and better connections.
It also claims there will be improced lounge, check-in and baggage privileges for loyalty scheme members and more opportunities to collect frequent flyer points.
IAG chief executive Willie Walsh said: "This expanded partnership complements the recent inclusion of Finnair into the joint business between British Airways and Japan Airlines. It has never been a better time to plan your journey across the globe."