American Airlines AAL.O has agreed to a provisional deal for 100 hydrogen-electric engines from aviation startup ZeroAvia, the carrier said on Tuesday, to power aircraft used in its regional routes.

The airline also increased its investment in the Hollister, California-based company as part of its Series C financing round, but did not disclose the details.

American first invested and signed a memorandum of understanding with ZeroAvia, which is flight testing a prototype for a 20-seat plane, in 2022.

The company is also designing an engine for larger aircraft such as the Bombardier BBDb.TO CRJ700, used by American on some of its regional routes.

ZeroAvia's hydrogen-electric engines has the potential for close to zero inflight emissions and use hydrogen in fuel cells to power electric motors to turn an aircraft's propellers.

"Advancing the transition of commercial aviation to a low-carbon future requires investments in promising technologies, including alternate forms of propulsion," American Airlines CEO Robert Isom said in a statement.

The carrier has set a goal to achieve net-zero greenhouse gas emissions by 2050.

Hydrogen is seen as a potential alternative for the aviation industry, a major user of fossil fuels. It can be made from fossil fuels or from water using electrolysis, although this is an expensive process.

(Reporting by Abhinav Parmar in Bengaluru; Editing by Vijay Kishore and Sriraj Kalluvila)