As part of its integration, American Airlines and US Airways announced it had expanded its codeshare agreement to cover 6,500 daily flights in the airlines' networks.
The company had initially added some codesharing between the two carriers on January 13 but this latest expansion covers almost all of the flights at American and US Airways.
American said there are still a few international flights that will not have a codeshare agreement because of regulatory requirements.
"Bringing the networks together is what this merger is truly about and is a prime example of how we intend to deliver exceptional customer service at the new American," American president Scott Kirby said in a statement.
Code sharing enables customers to buy a ticket for an American flight using the US Airways website and vice versa.