Since the systems make both airlines and travel agents more productive, CRS owners charge both of them for the use of their systems.Travel agents rent the equipment, while airlines pay a booking fee foreach flight reservation. American Airlines introduced the first computer reservation system; United, TransWorld, Eastern, and Deltaeach followed with systems of their own. American and United, however, dominate the CRS industry; in 1986, they accounted for 41 percent and 33 percent, respectively, of the flight segments bookedthrough computer reservation systems.The influence of computer reservation systems on bookings can beseen in two facts. First, a relatively large proportion of the travelagents in a city where a carrier operates a hub use that carrier's CRS.If the systems did not influence the behavior of travel agents, therewould be little reason for carriers to market them most aggressively incities where they center their operations. Moreover, at present all thecomputer reservation systems are owned and operated by airlines.While the airlines have found the systems to be profitable, the one system that was not owned by an airline has ceased operating. 16/