In a recent interview with the gaming TV show X-Play at the Game Developers Conference 2008, Portal lead designer Kimberly Swift confirmed that Portal 2 is in the works.
This was actually an accidental slip up on her part. To quote the below video: “I believe Doug Lombardi, who is our lead marketing director at Valve, has announced Portal 2.” While Valve hasn’t added to this statement, Mr. Lombardi in the past did state that “more Portal is definitely on the way,” according to X-Play.