Dead Island has shipped three million copies globally.
That's up from two million shipped in its launch month of September, publisher Deep Silver told Game Informer.
"Dead Island has sold very, very well over the holiday season and we are thrilled that it has sustained a robust level of sell-through since launch in September," marketing & PR boss Aubrey Norris said.
Last month, Dead Island developer Techland launched the Bloodbath Arena DLC for the game, adding a survival mode in which players fight off waves of zombies in four different arenas.
It was also discovered last month that the Polish studio had filed a trademark for 'Dead World' in the US, suggesting the zombie outbreak could be leaving the island of Banoi for a second game.