Wargaming.net’s free-to-play MMO World of Tanks is a hit, with over 20 million registered users. According to Wargaming’s CEO Victor Kislyi, the game is generating “double digit” million dollars in profit each month. The company has grown along with the game, too: over the past year and a half, Wargaming has expanded from 120 employees (nearly all located in Minsk) to over 800 staff members worldwide.

Of course, the numbers are sometimes misleading when it comes to free-to-play titles. While there are 20 million registered users, the percentage of those users who are paying for additional content is much lower. However, Kislyi has stated that among the large World of Tanks playerbase, about 25-30 percent of users are paying for content, which is one of the highest ratios in the industry.

One of the things Kislyi is most proud of is World of Tanks’ model for premium content. Unlike many free-to-play titles, World of Tanks doesn’t pressure the player into buying a ton of paid options. Kislyi explains that the “game is not squeezing monetisation” and “There’s no velvet rope over the gates and you have to buy a key to open it.”

World of Tanks has had a fast-growing fanbase through its two years of life. It first was launched in Russia in April 2010, then made its way to China, Europe, and the United States a year later. Most of its popularity remains in Russia, where it recorded 423,000 concurrent users. Europe typically lands about 85,000 online, while America gets up to 25,000. The numbers for China are unofficial, but estimates predict about 150,000 concurrent players.

There are about 400 employees working on World of Tanks, with another 150 working on the sequel World of Warplanes (not to be confused with that other “WoW” game) and another 70 working on World of Battleships.