The leaking well off the coast of Louisiana has spilled more than four million gallons of oil into the Gulf and continues to gush at a rate of 210,000 gallons per day. Why is this particular well spewing forth so prolifically, while in other places we have to pump oil out of the ground ourselves?
Because it's under a lot of heavy rocks. Deep deposits, like those in the Gulf, are packed down very tightly by the rock column above them. If they are tapped carelessly, the oil will start to gush out all at once, Beverly Hillbillies-style. Deposits that are closer to the surface are under less pressure, and the oil may need to be pumped from the very first drop. Almost all wells need a little help eventually, as extraction diminishes their internal pressure. Engineers pump water or natural gas into the chamber to force out the remaining crude, which is later separated from the added fluids.