Turbine's Dungeons & Dragons Online Eberron Unlimited has passed one million players since launch in September 2009, with revenues up 500 per cent since the game adopted a free-to-play model.
The game was subscription based until September last year, when an upgrade opened up a fee-to-play option - although subscribers have also doubled since the change, said the developer.
"The response from players to DDO Unlimited has been nothing short of phenomenal," offered Jim Crowley, president of Turbine.
"Weve known all along how great this game is and by implementing an innovative new model that put the players in charge of how they pay and play DDO Unlimited, weve successfully expanded our reach and injected new energy into the game."
The sale of content through microtransactions in Turbine's digital store are three times the industry average, according to the developer.
"The launch of DDO Unlimited has been a huge success and has really taken the game to a new level," added Fernando Paiz, executive producer of DDO Unlimited.
"As we celebrate our 4th birthday, the game has never been better and were just getting started with more adventure packs, more store items, and other innovative features coming in the major updates we have planned throughout 2010."