It’s easy to see why so many players love Rocket League, a video game that combines the thrill of racing with the strategy of sports, as the general idea is to knock a ball into a goal using all sorts of crazy driving tactics. But what’s really amazing is how successful the game has become even though the developer is giving away most of its content free of charge.

Forbes reports that revenue for the game has picked up tremendously over the past few months. Last December, it had grossed $70 million with four million copies sold, and now that number has ballooned to $110 million, and five million units sold. Its launch on the Xbox One platform almost certainly helped, but it’s still quite a win for a game that owes much of its success to being offered for free to PlayStation Plus subscribers when it first released.

“Our numbers are actually going up, not down,” said Psyonix vice president Jeremy Dunham. “Which is not very common for a game that’s ten months old.”

The game has garnered quite an audience between both eSports pro players and casual fans, with 15 million playing the game since its release last July.

Again, the complete surprise is with its business model. Although there are a number of premium cosmetic items, such as licensed vehicles from Back To the Future, Gears of War and Batman v Superman: Dawn of Justice, most of the updates are provided free of charge. But free content isn’t stopping the developer from gaining a hefty profit.

“We just want people to have options,” Dunham explained. “Where they can buy things that they think look cool that don’t negatively or positively affect their gameplay experience. We want people to express themselves, and so all the other items that we’ve done that do affect gameplay, like new maps or new modes, we give away for free. We don’t want people to feel like they’re not included in something if they don’t give us money. We want it to be the opposite.”

It’s certainly paying off, as approximately five million players continue to be active with the game, even months after its release. “One of the things you see in a lot of multiplayer games,” Dunham explained, “is that over time usually the player base gets smaller and smaller as more and more DLC is added to the environment, because fewer and fewer people are buying those items. Since we only sell cosmetic items and cars we aren’t cutting anyone out of the equation, and that’s why our numbers are actually going up month after month after month. Our active player base has been increasing for five months in a row.”

For example, the company released a new Hoops mode, where players try to slam a ball into a virtual net. Although the update was free, the game also released licensed NBA flags that players could attach to their cars for a small fee… which sold like crazy.

The company also continues to make strides with its community, having recently introduced a cross-play compatibility feature for Xbox One and PC, so players can take on one another no matter their platform. PlayStation 4/Xbox One cross-platform compatibility is still being discussed, but Dunham notes that “it’s one that we hope to deliver one day.”

And Psyonix isn’t done yet, as it has plans for future content down the road. “I think that’s one of the key elements in keeping a community healthy and going is not trying to create exclusive clubs where only certain people can play,” Dunham says. “We’re a community-based game so we want as many people to experience it as possible.”

As long as fans keep coming back with fun content and a strong community, Rocket League will continue to score big.