Under a strategic agreement signed in August 2016, Volvo supplied a smaller number of XC90s to Uber, which now form the backbone of the company's autonomous-driving test fleet. Uber previously used modified Ford Fusion sedans to test its autonomous-driving tech, although it never had an official relationship with the Blue Oval.

Uber is currently testing self-driving cars on public roads in Pennsylvania, California, and Arizona, but a shadow has been cast on the program in the form of an ongoing legal battle with Waymo. The former Google self-driving car project believes Uber used trade secrets stolen by engineer Anthony Levandowski. Uber also faces greater competition from rival Lyft, which has an alliance with Waymo and is getting more serious about self-driving cars.

If Uber really does buy up to 24,000 cars from Volvo, it would likely be the largest order of its kind to date. It could also give Uber a large enough fleet to start commercial autonomous ride sharing, although it's unclear if that is the company's goal. The ability to hail a ride in an autonomous is the end goal, but Uber may simply ramp up its testing program, taking advantage of new federal laws that expand safety waivers for prototype self-driving cars.

Agreements like the one between Uber and Volvo could become commonplace if self-driving cars become commercial realities. Tech companies developing autonomous-driving systems and ride-sharing services probably won't want to deal with the cost and complexity of building their own cars, meaning they'll have to rely on existing automakers for fleets of vehicles.