BioShock 2: official Announcement and rumours here

Take-Two has made official what everyone already suspected: a sequel to one of last year's biggest games, BioShock,will be coming in 2009. The game is slated to be released duringTake-Two's fiscal fourth quarter, which runs from August throughOctober, and will be developed by the publisher's newest studio, 2KMarin. This information comes by way of a report to investors, althoughof course in the Internet age that's nearly as good as a press releaseto get the information to the masses.
For those of you worried that Ken Levine, creative director for the first BioShock, will not be involved with the project, Take-Two is here to ease your worries. "[Levine] is critical to BioShock," the company told Shack News, explaining that he will be involved, although in what capacity we don't yet know.
This news goes along with Take-Two's previous plans, which involve releasing a sequel game every two years.No other information about the game was released, but many are bettingthat the next trip to Rapture will be in the form of a prequel.

The publisher's spoken of the possibility of hitting "roughly" a new BioShock release every two years.

"I would say, probably, roughly an every-two-year schedule would beoptimal. And if you look historically that has been largely the casewith GTA, and I'd expect we'd apply roughly the same strategy toBioShock because BioShock is shaping up to be a very importantfranchise", Take-Two chairman Strauss Zelnick has said in a conferencecall with analysts.

"I don't want to say more than that about BioShock because I certainlydon't want to jinx it, but I feel awfully good about where that'sgoing."