Looks like there are no borders when it comes to enthusiasm for Borderlands 2. Take-Two Interactive announced today that the game has sold more than 5 million units worldwide.

Developed by Gearbox Software and published by Take-Two’s 2K Games label, Borderlands 2 is one of the most popular games of the year. To keep it going, Gearbox is working on three new add-on campaigns for release in the coming months. The company has already released its new downloadable content: the Captain Scarlett and her Pirate’s Booty add-on campaign. And it has released an all-new Mechromancer character class that gamers can play in the title.

Borderlands 2, a sequel to the 2009 hit, is outselling the original title. The new game came out Sept. 18 and has an average Metacritic score (based on aggregated game reviews) of 90 out of 100.

“We’re thrilled with the momentum of Borderlands 2, and it’s really a testament to all the hard work that the team at 2K and Gearbox put in to make this a must play game,” said Christoph Hartmann, president of 2K. “The Borderlands series has never been more popular, and with continued support through substantial add-on campaigns, Borderlands 2 has cemented itself as one of the industry’s mega franchises.”

2K is selling add-on downloadable content (DLC) for $9.99 and is selling a season pass for content for $39.96.

“The overwhelmingly positive response to Borderlands 2 from our fans has been incredible,” said Randy Pitchford, President of Gearbox Software. “Players have embraced Borderlands 2 as their next hobby, with over 50 million interactions with Claptrap in the central town of Sanctuary and 12,000 real world years’ worth of time spent shooting and looting their way through Pandora! We are just getting started and have incredible momentum to improve and add to the game all the way through the holiday season and beyond. We can’t wait to show everyone what more we have in store for Borderlands 2.”

“The Borderlands franchise has redefined cooperative online gaming, and the original game’s ability to engage users years after its 2009 launch has been a guiding light for the rest of the industry,” said Jesse Divnich, VP of Insights & Analysis at research firm EEDAR. “Borderlands, has been able to achieve attach rates north of 25% when the industry average is 14%, and we anticipate that downloadable expansion packs for Borderlands 2 will generate similar attachment rates.”