United Airlines has made a commercial agreement with Denver-based aerospace company Boom Supersonic to add an aircraft to its global fleet and commit to a cooperative sustainability initiative.

Under the terms of the agreement, United will purchase 15 of Boom’s ‘Overture’ airliners, once Overture meets United’s demanding safety, operating and sustainability requirements, with an option for an additional 35 aircraft. The companies will work together on meeting those requirements before delivery. Once operational, Overture is expected to be the first large commercial aircraft to be net-zero carbon from day one, optimized to run on 100 percent sustainable aviation fuel.

“United continues on its trajectory to build a more innovative, sustainable airline and today’s advancements in technology are making it more viable for that to include supersonic planes,” United CEO Scott Kirby said. “Boom’s vision for the future of commercial aviation, combined with the industry’s most robust route network in the world, will give business and leisure travelers access to a stellar flight experience. Our mission has always been about connecting people and now working with Boom, we’ll be able to do that on an even greater scale.”

“The world’s first purchase agreement for net-zero carbon supersonic aircraft marks a significant step toward our mission to create a more accessible world,” said Blake Scholl, Boom Supersonic founder and CEO. “United and Boom share a common purpose—to unite the world safely and sustainably. At speeds twice as fast, United passengers will experience all the advantages of life lived in person, from deeper, more productive business relationships to longer, more relaxing vacations to far-off destinations.”