United Airlines UAL.O CEO Scott Kirby has pitched a combination with American Airlines Group AAL.O to numerous U.S. government officials, sources familiar with the matter told Reuters.

A combination of two of the largest U.S. network carriers would mark one of the most consequential consolidation moves since the last wave of airline mergers ended more than a decade ago, further tightening the domestic market already dominated by four players of roughly equal size.

It would potentially also redraw competition at key hubs such as Chicago and Dallas at a time when rising fuel costs are widening the gap between stronger and weaker airlines.

It was, however, not clear whether United has made any formal approach to American or whether a process was underway to pursue a deal. The sources spoke on condition of anonymity because the talks were not public.

United and American declined to comment on the potential combination, which was first reported by Bloomberg. The White House did not immediately respond to requests for comment.

American shares rose more than 5% in after-hours trading following the report, while United shares were little changed.

The U.S. airline industry is already highly concentrated, with American, Delta Air Lines DAL.N, United and Southwest Airlines LUV.N controlling the bulk of domestic traffic, each with a share of roughly 17%, according to Department of Transportation data.

U.S. Transportation Secretary Sean Duffy said this month that he thought there was room for consolidation in the U.S. airline industry, but said any potential deal would face close scrutiny on how it would affect consumers.

American has been under pressure to improve profitability and close the gap with Delta and United, after unions earlier this year criticized management over lagging returns. The airline has pointed to strong premium demand and corporate travel to drive a recovery in 2026.

American is by far the smallest of the big four U.S. airlines by value, with a market capitalization of $7 billion, compared with $31 billion for United, $19 billion for Southwest and $44 billion for Delta.

United, by contrast, has struck a more confident tone as high fuel prices test the industry, with Kirby recently saying a prolonged cost shock could create opportunities for stronger airlines to gain share as weaker rivals struggle.

Kirby previously served as American's president from 2013 to 2016.

-David Shepardson and Rajesh Kumar Singh/Reuters