This July, gamers from all over the world will fly into Seattle to partake in and watch one of the biggest e-sports events on the globe.

The International, developer Valve’s championship for its free-to-play online action-strategy game Dota 2, begins July 18 in Seattle’s Key Arena, and this year’s event is the biggest one yet. That’s not just in terms of the people watching in person and online but also in terms of the amount of money at stake. Dota 2 fans have pushed the overall prize pool of The International over $6 million, and that number will only get bigger between now and the start of the tournament.

This guarantees that The International 2014 will more than double the previous biggest e-sports prize pool, which was last year’s International at $2.9 million. Other large tournaments in 2014 include the $1 million Call of Duty Championship and the League of Legends Season Four Championship with an undetermined prize pool.

Valve started 2014’s purse at $1.6 million, which is already a hefty sum for a competitive-gaming event, but fans of Dota 2 have contributed a couple extra million by purchasing The International Compendium. This is a e-booklet that gives gamers a number of ways to interact and keep up with the event. It also gives them ways to earn points by watching, which will then turn into virtual goods they can use for their own Dota 2 characters. The Compendium sells for $10, and Valve takes $2.50 of each one sold and adds it to the prize pool. Valve then also uses some of that money (in combination with ticket sales) to pay for operating the event itself.

Dota 2 fans can watch the event live on the streaming site Twitch just like millions did last year. Major championships like The International are one of the main reasons the gameplay video site is so popular and potentially worth the rumored $1 billion that Google is supposedly going to paying for it.

This marks the fourth year of The International. In 2013, the top Dota 2 teams competed over a $2.9 million prize pool where first place took home approximately $1.45 million (or 50 percent of the total).

Dota 2 is one of the top competitive games on the market right now, and Valve is doing everything it can to boost its stature among hardcore players. The Compendium is one way of doing that. Players who spend the $10 on the virtual booklet only get a few minor things. To maximize the value of the purchase, they must complete quests that mostly revolve around watching The International.

Fans get points for picking a favorite team, predicting the qualifiers, and picking the top six teams. These points then upgrade the Compendium and unlock all kinds of special items and features in the game.

Of course, players can also purchase points with real money. Valve sells packs of up to 2,400 Compendium Points for $10.

E-sports is a fast-growing part of the gaming industry. Games like Dota 2 attract millions of players who compete casually as well as thousands who attempt to go pro. More than 32 million people watched last year’s final match for the League of Legends championship. While these e-sports events attracts lots of eyeballs, most game publishers and developers treat competitive gaming as a marketing tool and not as a primary source of revenue.