Shivering isles was the first and probably the last!

The producer of Bethesda studios was recently asked if they are working on any more expansion packs for Elder Scrolls IV: Oblivion:

"We have pretty much everybody on Fallout 3 right now, It started off kind of small and then we add people to it and now the expansion's done, all those people have come on to Fallout 3. That's the thing we want to focus on right now, so I think I'd be surprised if we do another expansion"

So why not have another studio work on future expansions? this was the response:

"really getting into the stuff we're doing with Elder Scrolls and Fallout and I guess we're shy about having someone else start making content."

I guess that makes sense!