In August, the carrier backed Archer Aviation, and now it’s invested $15 million in Eve Air Mobility, an Archer rival. Its new order will see another 200 of the four-passenger vehicles eventually make their way to United, perhaps as soon as 2026. The company also has an option to buy another 200.

Investing in two different manufacturers isn’t unusual. Many airlines, for instance, have both Boeing and Airbus planes in their fleet.

The company is wagering that flying taxis will become a big business in the coming years. To date, though, the Federal Aviation Administration has not yet cleared those vehicles to begin ferrying passengers.

The vision for these aircraft is for them to transport customers around cities to hub airports, letting people bypass crowded highways and make more efficient use of their time. The FAA is in the process of determining how to integrate them with existing flight patterns (most flights are expected to take place between 2,000 and 3,000 feet above ground level) and requirements for pilots.

“United has made early investments in several cutting-edge technologies at all levels of the supply chain, staking out our position as a leader in aviation sustainability and innovation,” said Michael Leskinen, president of the investment arm United Airlines Ventures, in a statement. “Our agreement with Eve highlights our confidence in the urban air mobility market.”

Aircraft classified as eVTOL (electric vertical takeoff and landing) have the ability to take off and land much like a helicopter, meaning no runway is required. They’re designed to be quieter than cars or even air-conditioning units. Because they’re electric, they also claim to reduce carbon emissions.