This July, Valve will kick off The International, its annual championship for wildly popular free-to-play competitive game Dota 2. The action will likely be as intense as ever, but this year there's much more at stake thanks a staggering pool of more than $6 million. That's more than double last year's event, which featured a prize pool of $2.8 million, $1.4 million of which went to the winning team. If this year's competition includes the same cash distribution, the winners are in for quite the payout.

Most of the prize money comes from fans

What's particularly interesting is the way developer Valve managed to raise such a large sum. Fans are able to buy a virtual book called The Compendium, which offers different ways to interact with the upcoming tournament, as well as keep up to date with everything that's going on. "It's the next-best thing to being there," the company says. Each book costs $9.99, $2.50 of which goes towards the prize pool. Valve also offered a number of stretch goals to encourage more purchases, including additions like better music and emoticons for in-game chat. Passing the $6 million mark means players now have the option to customize their in-game bases. Some of the prize money comes from Valve itself, but more than $4 million (and counting) comes directly from fans purchasing these books.

The huge cash prize is just the latest development in the incredibly rapid ascent of e-sports. Last year more than 30 million people watched the championship for Dota 2's biggest competitor, League of Legends, while even those who make in-game items are making money. Meanwhile, streaming service Twitch has seen a large burst in popularity due largely to the booming e-sports market. Twitch is reportedly being acquired by Google for $1 billion after turning down offers from Microsoft. As for Dota 2, you'll be able to see just who will get their hands on that prize money later this year, when The International kicks off on July 18th in Seattle.