Previous announcements have stated that TES V would be built on a new version of the Gamebryo engine used in Oblivion and Fallout 3/New Vegas, but a Tweet from Bethesda Community Manager Nick Breckon stated, "We can now confirm that the TES V: Skyrim engine is all-new. And it looks fantastic." A followup answer stated that the engine was "a new graphics/gameplay engine built internally" and that more details would be forthcoming.
--- "64 inches? Thats, like, longer than a freaking football field!" -some guy on XBL