While there's probably oil under Gull Island, it's doubtful it's enough to fuel America for 200 years. That would be nearly as much oil as there is in the world. Hard to believe BP wouldn't exploit some of it at $140 a barrel. More likely they're waiting for the rest of Prudhoe Bay to run dry and then switch to Gull Island. That would keep the oil flowing through their pipeline without having to build a new one.

I believe that was their initial thinking and may still be the right strategy, but Prudhoe Bay has lasted longer than they thought it would and they may have to rebuild the pipeline before Gull Island comes into play.