Microsoft is tooting its horn that first week sales of its new Halo 3 video game has crossed $300 million making it the fastest selling game ever.

Released on September 25, Halo 3 is the final version of a popular trilogy developed exclusively for Microsoft’s Xbox 360 video game console.

In the first 24 hours of its launch, Halo 3 sales in the U.S. reportedly reached $170 million.

Microsoft executives say over 20 million copies of the games in the Halo trilogy have been sold worldwide.

Xbox 360 sales are also supposedly seeing a surge since the release of Halo 3, with Microsoft claiming a doubling in the weekly average sales of the consoles.