Budget airline Ryanair has signed a deal to buy 27 737-800 planes from Boeing worth a possible $1.9bn (£960m).
Passenger growth is expected to boost Ryanair results out next week
The aircraft will be delivered between 2009 and 2010, increasing the Irish carrier's total fleet to 262 by 2012.
Ryanair said the planes would be fitted with technology to reduce fuel burn and carbon dioxide emissions.
Ryanair boss Michael O'Leary has said in the past that "the recent hysteria" over the impact of flying on climate change is "misguided and misplaced".
Mr O' Leary says aviation accounts for less than 1.6% of greenhouse gas emissions.
In buying the environmentally-friendly 737-800, the group said it was "strengthening Ryanair's position as Europe's cheapest, greenest and cleanest airline".
"Ryanair guarantees passengers that they will not find a cheaper fare with any other airline on any of its 487 routes," added Ryanair's chief financial officer Howard Millar.
"The combination of the lowest per seat operating cost and the reliability of these Boeing 737 800s will benefit millions of additional passengers in the coming five years as we extend our route network and our guaranteed lowest fares."
The fast-expanding no-frills airline, which is due to report its annual results next week, is waiting for the conclusion of a European Union investigation into whether its proposed takeover of rival Aer Lingus would hamper competition in the airline industry.