Eidos Interactive has announced an agreement with Microsoft to release two downloadable chapters for Tomb Raider: Underworld exclusively for the Xbox 360.

Containing up to six hours of new gameplay and content for Tomb Raider: Underworld, the chapters will be available exclusively on Xbox Live Marketplace for the Xbox 360. A demo for Tomb Raider: Underworld will also be available on Xbox Live Marketplace in October.

Offering entirely new content, the two chapters - Tomb Raider: Underworld - Beneath the Ashes and Tomb Raider: Underworld - Lara's Shadow - will deliver two very different single player gameplay experiences. Tomb Raider: Underworld - Beneath the Ashes takes place after the Underworld story has finished and will feature a new environment to explore, additional secrets to unlock and different enemies to fight. And Tomb Raider: Underworld - Lara's Shadow will introduce players to a "new kind of playable character".

The first new chapter, Tomb Raider: Underworld - Beneath the Ashes, will be available for download exclusively on Xbox Live Marketplace this Christmas. Tomb Raider: Underworld - Lara's Shadow will follow in early 2009.

Tomb Raider: Underworld will release on the Xbox 360, PlayStation 3, Wii, PlayStation 2, DS, and PC.