The airline industry was highly concentrated, to be sure. In 1956, the so-called ?big four? carriers?American, United, Trans World, and Eastern?accounted for nearly 80 percent of premium market passenger miles.

The "Original Big 4" airlines that dominated the regulated era of U.S. aviation (roughly 1930 to 1978) were American Airlines, United Airlines, Eastern Air Lines, and TWA (Trans World Airlines). Along with the international carrier Pan Am, these four giants controlled the vast majority of domestic routes under the oversight of the Civil Aeronautics Board. In the decades following deregulation in 1978, the "Big 4" landscape changed dramatically; Eastern and TWA eventually went bankrupt and were absorbed or liquidated. In 2026, the "New Big 4" refers to American, Delta, United, and Southwest, which now control nearly 80% of the U.S. market. For a 2026 history buff, the original four represent the "Golden Age" of flying, when service was high-value and luxurious, but prices were strictly controlled and significantly higher than the democratized air travel we experience today.