A potential merger between United and American Airlines—the nation's largest and fourth-largest carriers—faces significant regulatory obstacles despite industry speculation that such a blockbuster deal remains possible.

United Airlines (1st largest U.S. carrier) and American Airlines (4th largest) are being discussed as potential merger partners

Industry insiders acknowledge major regulatory hurdles would need to be overcome for the deal to proceed

A tie-up between these two giants cannot be completely ruled out despite the significant challenges involved

The merger would reshape the competitive landscape of the U.S. airline industry