We test whether airline consolidations generate monopoly profits by examining returns to listed carriers around horizontal airline-acquisition bids and evaluating effects of industry concentration on share-price reactions. Under Civil Aeronautics Board (CAB) regulation, returns to targets, bidders, and rival carriers are positive functions of changes in concentration implied by bids. Changes in concentration after deregulation have no positive effect on carrier returns. These results support Jordan's (1970, 1972) hypothesis that CAB activities fostered carrier collusion. There is no evidence of monopoly gains from carrier consolidations after deregulation.