Activision, the company behind triple-A titles like the Call of Duty franchise announced today that it has sold more than 18 million map packs for its latest game.

The map packs sell for $15 each and serve as an expansion to the retail game, which sells for around $60. The map packs, which are add-ons for the game, feature new levels for multiplayer matches and are a lucrative business for Activision Blizzard. Both previous map packs are the highest-selling add-ons on Xbox Live, according to Microsoft.

Activision now makes around $76 per copy of Call of Duty: Black Ops sold, which is 18 percent higher than traditional retail costs for triple-A video games with high production values like the Gears of War and Battlefield franchises, Activision Publishing chief executive Eric Hirshberg said. The company started selling map packs in 2008 when it released an additional map pack for Call of Duty: World at War, which sold 9 million units at $10. Activision also released map packs for Call of Duty: Modern Warfare 2, which moved 11 million units at $15.

The company’s next game, Modern Warfare 3, comes out this fall, and there’s a good chance that the company will sell map packs for that, too. Activision is also releasing a premium social network of sorts for its Call of Duty franchise alongside Modern Warfare 3. Call of Duty players typically spend more time playing the company’s games than they spend on social networking sites like Facebook, Hirshberg said.

“We expect to break last year’s pre-order margin by a significant amount,” he said. “Black Ops sold 23 million HD units in nine months into an install base of more than 74 million high-definition consoles, and  there’s 20 percent expected growth in the high-definition console install base.”

Call of Duty Black Ops is one of the best-selling video games of all time, with sales of more than $1 billion since the launch last November. Activision Blizzard previously launched its First Strike map pack in February. It launched its most recent map pack, Escalation, in May.