United Airlines is ordering 35 Airbus A350-1000s which will include conversion of 25 previously-ordered A350-900s to the larger model.
The carrier's order comprises 10 additional aircraft on top of the conversion, Airbus confirmed during the Paris air show.
A350-1000s will be exclusively powered by Rolls-Royce Trent XWB engines. United expects to take delivery from 2018.
Check out the latest news and views from this year's Paris air show, including:
Finally, our new-look iFDN editions will contain exclusive footage from Paris 2013. Find out more