For reasons that are not clear, Rockstar's Grand Theft Auto IV is no longer available to purchase on Steam. A member of the ResertEra forum recently discovered that the Steam page for GTA IV no longer has a purchase button where it once was.

The page does not offer any insight into why this is the case. Rockstar Games could not be reached for comment at press time.

People are speculating that this has something to do with music licensing or how GTA IV still requires a Games For Windows Live account. Others are guessing that Rockstar might be moving GTA IV from Steam to its own Rockstar Launcher. For now, the real reason why GTA IV is no longer available to buy on Steam remains a mystery.

PC Gamer reminds us that Rockstar removed GTA Vice City from Steam for a brief period of time in 2012 due to a copyright claim related to the Michael Jackson song "Wanna Be Startin' Something."

Grand Theft Auto V and Grand Theft Auto: San Andreas remain available for purchase on Steam. It's also worth noting that those who already own GTA IV on Steam can continue to play the title.