The two airlines announced on Friday that they have agreed to open their books for mutual inspection.
Company officials were at pains to state that the confidentiality agreement did not signal an actual merger, merely that the airlines were discussing the possibility of combining their operations, the Associated Press noted.
Shares of US Airways rose almost 4% on the news in Friday morning trading.
AMR, which owns American Airlines, has been in bankruptcy proceedings since last year. It has been attempting to reduce costs and renegotiate contracts with its employee unions.
Earlier this month, American persuaded its flight attendants to accept a new contract, leaving only its pilot union without a deal. The company needs to complete deals with all its unions before it can emerge from bankruptcy.
American officials have strongly hinted in recent months that they are looking for a merger partner.