The structure of the US airline industry has undergone important changes since the deregulation in 1978, which removed entry and exit restrictions and allowed carriers to set airfares. One of the most dramatic aspects of the airline deregulation has been the shift of carriers from a point-to-point business model to hub-and-spoke (HS) networks, where a carrier designates one or more strategically located cities as hubs. Passengers are first channeled to the hub, and only then are taken to their respective destinations. Initially, the termination of unprofitable lines, increased productivity, and other general cost-reduction policies amplified profitability in the market. Changes in the market, however, and in particular the entry of direct carriers have increased the competitiveness of the market and during the last decade the airline industry has been facing a financial crisis. We propose an economic model that analyzes the equilibrium market structure in the competition between a direct carrier and a hub and spoke carrier. The model departs from traditional economic models of the airline industry by separating the hub carrier's decision to service a city and the carrier's pricing decisions for city-pair routes. The model is tractable and has several key properties: The inter-dependence between routes is derived from either capacity constraints or demand uncertainty, both of which are modeled explicitly. The hub carrier's inherent cost disadvantage, due to the longer routes implied by a hub and spoke system, is mitigated by consumers’ benefits from the hub's network, the HS better load factor as well as its better risk pooling. Based on these tradeoffs, the model can quantify the advantage HS carriers should achieve in any of the dimensions above in order to compete effectively with a direct carrier.