InviseoMedia, which sold the seatback advertisements to Ryanair and to another European low-cost carrier, Germanwings, says the system provides an average of 40 minutes of “dwell time” during a typical flight. In other words, the only ways for passengers to avoid the advertisements, which are placed behind tamper-proof plastic shields, is to open the tray or get up and stretch their legs. And when they do that, they are confronted with the advertisements on the overhead bins, which are being sold by a separate company, Fourth Edition.

“It’s a good medium, a good audience and they’re captive to some extent,” said Dominic Stead, the chief executive of Inviseo. “In this day and age, the opportunity to get someone’s attention and hold it is invaluable.”

Inviseo began installing its panels in Germanwings planes about two years ago, and companies like Microsoft, DaimlerChrysler, Hewlett-Packard and HRS, a German travel Web site, have advertised on them.

Since the seatback advertising space became available in Ryanair planes this summer, it has attracted one advertiser, Creative, a maker of digital entertainment devices, which has bought space in a handful of planes. But Mr. Stead said the Inviseo system could be popular with advertisers that link advertisements to mobile phone call-in and text-message campaigns, because Ryanair and a number of other airlines plan to enable in-flight cellphone use soon.

The overhead bins have had a slightly faster uptake than the seatbacks at Ryanair, with advertisements being placed by companies like the Dutch bank ING; Red Bull, the energy drink; and Meteor Mobile Communications, an Irish cellphone operator. Martin Barry, managing director of Fourth Edition, said the advertisements could generate annual revenue of 6.5 million euros, or $8.8 million, if all 41 panels on every one of Ryanair’s 137 planes were sold for an entire year. Like Inviseo, Fourth Edition splits an undisclosed portion of the proceeds with the airline.