Sony Online Entertainment's free-to-play online world Free Realms now has 20 million registered users.
"This benchmark is an honour and a true testament of SOE's success with free-to-play games," said SOE president John Smedley in a statement.
"Free Realms delivers a truly captivating, quality gameplay experience that keeps our community engaged and continues to attract new players every day."
Free Realms launched in May 2009, and passed 12 million registered users in April the following year.
In an interview with GamesIndustry.biz earlier this year, Smedley stated his belief that the Free Realms community could eventually grow to 100 million.
Sony converted its subscription-based MMO DC Universe Online to free-to-play this month. In an editorial for GamesIndustry.biz, published the day the decision was announced, Smedley predicted that Star Wars: The Old Republic would be the last "large scale" MMO to use the subscription model.