Wargaming Chief Executive Officer Victor Kislyi thinks that free-to-play games like World of Tanks are viable for the Oculus Rift only if it sells 10 million units.

He said that he tested the device in San Francisco and was impressed with it, but that the games his company makes won’t work on any platform until it reaches a certain player base.

“75 percent of our players will never pay us a penny,” Kislyi told CVG. “For other games this percentage can be bigger, up to 90-95 percent of people just playing for free.” In order for that business model to work financially, he explained, Wargaming needs at least 5-10 million people playing the game. “If Xbox One or Oculus Rift reaches those numbers, we’re there,” Kislyi said.

As Oculus VR founder Palmer Luckey explained, the desire to reach an audience of that size (and much bigger) was one of the main reasons he agreed to Facebook’s $2 billion acquisition.