(Waymo/Avis Budget Group)

One of the nation’s biggest rental-car companies will be supporting Alphabet’s latest venture into self-driving cars, the two firms said Monday.

Avis Budget Group, the company that owns the Avis, Budget and Zipcar brands, has signed a deal to help maintain Alphabet’s self-driving car fleet in Phoenix, which began serving members of the public in April.

The pilot program in Arizona has been picking up passengers and dropping them off as part of an experiment tinkering with the future of transportation. Waymo’s test is an effort to understand where people want to go with self-driving cars, and how they interact with them. It’s similar to the one Uber launched in Pittsburgh last year involving the company’s own self-driving cars.

Under the terms of Monday’s deal, Avis Budget Group is expected to care for Waymo’s fleet of Chrysler Pacifica minivans and other vehicles forming the backbone of Alphabet’s planned 600-vehicle fleet in Phoenix. Avis will clean the cars, as well as perform regular maintenance such as oil changes, tire rotations and installing ordinary replacement parts.

“This partnership will allow Avis Budget Group to service Waymo’s growing number of cars on the road, ensuring Waymo’s self-driving vehicles are ready for riders around the clock,” the two companies said in a statement.

The maintenance deal does not appear to extend to the actual rental of self-driving cars; riders who wish to use Waymo’s vehicles must apply for permission to participate in the company’s early rider program. Still, the deal highlights the way that rental companies, with their nationwide scale and experience maintaining vehicle fleets, could become key players in the spread of self-driving technology.

Transportation experts expect that in densely populated areas, self-driving fleets such as Waymo’s could soon become the norm. Ride-hailing companies have already demonstrated that calling a car to your location on a smartphone is easy; now, analysts say, the next step will be to automate the driving itself so that the cars can run more efficiently.

Waymo’s selection of Avis as a partner was no accident, according to automotive analysts. By working with a company that lacks an existing stake in self-driving cars, Waymo could avoid giving other car companies a glimpse into its efforts.

“[It was] likely done in an effort to hedge against automakers’ race to develop their own autonomous technology,” said Tony Lim, an analyst at Kelley Blue Book.

Monday’s partnership between Waymo and Avis was followed hours later by reports that Apple had signed an agreement with Hertz, another major car rental firm. Apple is currently researching self-driving technology on Lexus SUVs, vehicles that are being supplied by Hertz’s fleet management unit, Donlen, according to Bloomberg News.

Shares of Avis Budget Group briefly surged 20 percent on the news before closing up 14 percent Monday. Shares of Alphabet closed down 1.42 percent.