Just a few years ago, they were giving land away for free in North Dakota in an effort to stop the outflow of residents. Of course, all those programs have stopped now.
On another note, most if not all of these fields were discovered in the '50's - they simply did not have a way to get the oil out of the ground in those days. It makes you wonder if in the future, they'll be able to get even more oil out of old wells that have been "pumped out" by old methods, but with new methods, they can be opened again and produce even more oil.