In this paper, we determine characteristics of the cost-minimizing airline
network under economies of density. Airline demand is asymmetric and govern
ed by the gravity model. Airline networks are restricted to those where eac
h spoke city is assigned to a single hub and where hub cities are fully int
erconnected, The cost-minimizing network is a mixture of a point-to-point a
nd a single hub network. Multi-hub networks where passengers change planes
at more than one airport are found to be suboptimal. (C) 2001 Elsevier Scie
nce Ltd. All rights reserved.