Sony Online Entertainment's free-to-play MMO Free Realms is 'close to' 5 million registered users, revealed Sony Online president John Smedley, speaking in a Gamasutra-attended panel at Comic-Con International San Diego 2009,

And DFC analyst George Chronis estimated that right now, 33 percent of United States game revenue comes from MMOs.

Launched this past April, Free Realms reached a player base of 1 million in only ten days, and has seen a series of statements from SOE as that figure has ticked up by the million every several weeks.

Smedley credited the success to the free-to-play business model, which relies on microtransactions for revenue.

The company has also implemented officially-sanctioned microtransactions into its existing subscription-based games EverQuest and EverQuest II, and the exec said user adoption has been strong. “We now have 34 percent of our EverQuest II users using microtransactions,” he said, with the original EverQuest at a slightly lower percentage.

The figures came after several statements by fellow panelist Min Kim, of South Korea-based MMO developer Nexon, which relies heavily on the free-to-play model with its games like Maple Story.

Kim described the company's Asian games as “truly massive,” based on the incredible percentage of South Korean citizens who play their games – as verified by social security numbers. “I think it's because we changed our business model and made all the game free,” he said. “Once they get into the game, we have to earn our paycheck.”

“When people started talking about it back in 2003 or 2004, people said Western games would never want to do this, to play a game for free and then buy and items. And now everybody is saying, 'We're going to have microtransactions as part of our business model.”

He credited his company's successful introduction of the MMO Maple Story to the West. With Maple Story's revenue accrued in 2007, microtransaction revenue provides the equivalent of about 120,000 monthly paying users in more traditional subscription-based games. The game reaches over 6 million free and paying registered users in the United States with little marketing effort so far.

Smedley agreed with Kim about the effectiveness of free games and microtransactions: “They have an item that allows you to become a moderator in a chat room and kick people out. It's awesome.”

DFC analyst George Chronis, serving as panel moderator, shared some of his firm's outlooks and statistics on the market. “When something gets popular, like Ultima Online did and EverQuest did, everybody rushes in,” said Chronis. “And World of Warcraft added a lot of interest, but MMOs are changing,” he said, referring to other MMO models like the free-to-play approach taken by many Asian publishers.

DFC expects that in 2013, 72 percent of MMO revenues will be coming from PC games, and 28 percent from console games – and, “right now, 33 percent of revenue generated by games in the United States is generated by people playing MMOs.”

[UPDATE: According to SOE representatives, Smedley announced that Free Realms was "close to" reaching the 5 million milestone, but has not yet reached it. Gamasutra has amended the story accordingly.]