I take it you missed the comment that the entire population of the planet could live within the borders of the state of Texas and be no more crowded that the island of Manhattan?
Space isn't the issue. Food is. And farm land. Regardless of how packed people get, you still have to get them the food from the farms. So that means oil, as well.
"A casual stroll through the lunatic asylum shows that faith does not prove anything." - Friedrich Nietzsche