For a large international airline, The Brattle Group provided expert analysis opposing a request by SkyTeam alliance members for expanded antitrust immunity. We replicated and updated previous studies by the U.S. Department of Transportation (DOT) to show that, since 1999, air fares had increased sharply in transatlantic markets dominated by immunized alliances relative to other transatlantic markets, a turnaround of earlier fare trends. Our analysis found that this turnaround was due in part to the exercise of market power by the immunized alliances.