Oil well ignorance (mine)

What makes the oil continue to flow at the spill? I mean it's a
mile deep with tons of pressure on it and the wells I'm used to seeing
all have those little grasshopper pump deals. I thought you had to
pump the oil out or force in something else to force the oil out.
If there is so much pressure in the oil field itself that it overcomes
the pressure of the sea then why don't we have natural oil flows all
over the world like magma coming out under pressure in volcanic areas?


Larry L ( who it seems doesn't have a clue how an oil well works )