This paper empirically investigatesthe effects on air fares, passenger volume, andconsumer surplus of four major alliances in NorthAtlantic aviation markets. The four alliances areBritish Airways/USAir, Delta/Sabena/Swissair,KLM/Northwest, and Lufthansa/United Airlines. We findthat equilibrium passenger volume increased by some36,000 passengers annually and equilibrium air faresdecreased by an average of $41 on the routes servedby the allying carriers, and that consumers weregenerally better off due to the alliances.