Greenest airline

http://www.ryanair.com/ie/news/ryanair-the-world-s-cleanest-greenest-airline-celebrates-world-environment-day

Ryanair, Europe’s only ultra low cost airline, today (5 June) celebrated World Environment Day with the publication of independent research which confirmed Ryanair is the world’s cleanest, greenest airline as it urged ‘people who care’ to fly Ryanair.
The in-depth Brighter Planet research report on the world’s 20 largest airlines showed that Ryanair is the most efficient, and with an average fleet age of less than three years any passenger that flies on Ryanair’s low fares ensures that their flight is the greenest, cleanest, flight possible.

http://www.ryanair.com/doc/about/ryanair_brighter_planet_2011.pdf