Iberia will return to the Sabre system on Monday, after having withdrawn on June 12.

Development of the Sabre system started, which many computer historians have suggested was one of the major milestones in the commercialization of computers.

American Airlines, for one, has been aggressively trying to establish its sophisticated Sabre system in Europe.

American started installing Sabre systems in travel agencies in 1976.

American already holds a dominant share of the market with its Sabre system.

Under the agreement, Delta would pay American Airlines $650 million for access to the Sabre system, which serves about 38 percent of travel agents.

Southwest schedule and fare information is still available to travel agents who use the Sabre system, owned by American Airlines.

United also owns 50 percent of the Covia computer reservation system, second in market share only to American's Sabre system.

Three years ago US Airways switched to the Sabre system after months of training.

Another example is the Sabre system that has been designed for making reservations but has been used in crew scheduling and flight forecasting.