The website explained that reservations ensure that the passenger gets two adjacent seats at the same rate.
For those who do not reserve two seats in advance, an airport agent will find out if two seats are available together.
If the passenger is offered a seat in a higher class of service that offers more space, the passenger may be eligible for the fare difference.
If no adjustments can be made on the original flight, the affected passenger can purchase seats on another flight at no additional cost.
American Airlines also offers several seat options, including Flagship First, Flagship Business, First, Business, Premium Economy, Main Cabin Extra, Main Cabin, and Basic Economy.