Yesterday, someone spotted one of Apple’s newly licensed self-driving cars puttering around in Silicon Valley, and — surprise! — it was a white Lexus RX450h. This wasn’t a total shock — after all, Apple registered three Lexus SUVs with the California DMV for autonomous driving earlier this month.

But the extent of Lexus’ popularity among those conducting self-driving experiments is pretty amazing. Not only is Apple using the luxury car brand as a platform to test its software, but so are many other operators. It’s essentially a free advertisement for Lexus’ parent company, Toyota (which prefers the Lexus LS 600hL for its own self-driving tests).

Lexus RX SUV is the top choice among driverless operators

Lexus may be the most high-profile brand on the road but there are other makes and models used for self-driving tests by companies playing in this space, including the Ford Fusion (Uber, Udacity, and obviously Ford) and the Lincoln MKZ (Faraday Future, Drive.ai). Volvo’s safety record makes it a popular choice as well.

What goes into the decision-making process for choosing a self-driving test car? Battery capacity, cargo space, and all-wheel drive are just some of the considerations made by self-driving operators. According to Sam Abuelsamid, senior analyst at Navigant, the higher the autonomy of the vehicle, the more electricity required to power the car’s self-driving hardware.

“A conventional [internal combustion engine] vehicle with a 12-volt electrical system only offers about 2.5 kilowatt of electrical power max and on most modern cars they are close to maxed out,” Abuelsamid said. “Highly automated vehicles (Level 4 and up) will probably require 48V systems at a minimum.”

Brand familiarity is another driving factor. Both the Lexus RX and Ford Fusion have been around for so long, their hardware is “pretty well understood” by many in the tech world, Abuelsamid said.

“For years people having been hacking older Priuses to convert them [plug-in hybrid electric vehicles],” he added. “Ford Fusions are also widely used by Ford as well as Uber for pretty much the same reason, available and understood. Some companies such as Nvidia are using the Lincoln MKZ which is mechanically identical to the Fusion.”

And the space required by autonomous vehicles is huge. All those sensors, processing, and upgraded actuators take up a ton of space. Abuelsamid shared this photo of the trunk of one of Ford’s autonomous Fusions to drive home the point about why SUVs and minivans are so popular these days.

What is everyone else using? Here is our best effort at compiling a comprehensive list. There are over two dozen companies licensed for autonomous testing in California alone, and we’re on the lookout for the next model — another SUV or something a little sassier.

Waymo (née Google): Chrysler Pacifica and Lexus SUV

Uber: Ford Fusion and Volvo XC90

Apple: Lexus RX450h

NuTonomy: Renault Zoes and Mitsubishi i-MiEV

Baidu: BMW and BAIC

Udacity: Lincoln MKZ

Ford: Ford Fusion

General Motors: Chevy Bolt

Bosch: Tesla Model S

Delphi: Audi SQ5

Nvidia: Audi Q7

Comma.ai: Acura ILX

Nissan: Nissan Leaf

Volvo: Volvo XC90

And last but not least... the Google car