Calchas

Airlines offer their products through many channels.

The traditional channel is to publish their fares, their schedules and the availability on each flight onto what is called a "GDS" or global distribution system.

This system is how a travel agent in rural China can see that there is one seat left on your preferred LAX-JFK flight tomorrow afternoon. He can book it using the Computer Reservation System and be sure that no one else, even if they book it at the same time, will clash and overbook the plane (at least, this can happen, but only if the airline allows it).

The ITA Matrix presently uses this system to gather fare information, and to compute the lowest price available for you under a given set of circumstances.

But there are other ways airlines can sell their products. They can negotiate individual arrangements ("corporate fares") with large travel agents and large corporates, which are not publicly available. ITA cannot see those, and nor can anyone else.

Airlines nowadays also sell their products directly to customers, either online or by phone, or at the ticket desk. For a while, these channels simply mirrored the public information that was distributed to travel agents. For most airlines, such as British Airways, this remains the case. Many airlines, however, sometimes also offer cheaper deals on their websites (such as Cathay Pacific).

But there is a fee to join these global distributions systems. Some airlines, such as Easyjet and Ryanair, decided to sell their products directly to customers only, and bypass this whole travel agent business, which at the time also garnered agency fees for the agents that the airlines had to bear.

Ryanair continues with this paradigm, for now, but it is likely to change soon.

Other online booking sites often "scrape" the carriers' websites, that is they pretend to be a person looking at the site to obtain a fare quote. But ITA Matrix does not do this, it only uses publicly published information.