Well, I was more specifically talking about the oceans. Crude oil comes from the depths of the sea, and if people owned the oceans, there would be competing land/water owners, and thus competing prices for oil.
OPEC is a group of oil exporting countries in the middle east and they price fix, so no one can sell oil cheaper due to the fact that waters off-shore aren't privately owned. Even if we allow BP to offshore drill, they're part of OPEC, so prices won't really go down enough.