Activision has sold 18 million Call of Duty: Black Ops map packs, the publisher has announced.

CEO Eric Hirshberg revealed the figure during an investor event in Los Angeles earlier today, adding that users have spent an average of $76 on the game - an 18 per cent increase on the sticker price.

In comparison, World at War sold nine million map packs in its first nine months on sale. At $10 per pack, that equated to an average user spend of $68. Modern Warfare 2 sold 11 million downloads over the same time period, at $15 each.

Hirshberg went on to claim that "consumer engagement" in its FPS franchise is at an "all time high".

"There are over 30 million unique players of Black Ops who collectively have amassed, incredibly, more than 2.3 billion hours of play. To put that number in perspective, that's more than a quarter of a million years of play and that means our millions of fans spend more time per day on Black Ops multiplayer than they do on Facebook."

The next entry in the series, Modern Warfare 3, arrives this November. Map packs may well follow.