Subject: When oil is extracted , what happens to the space that the oil occupied?

Dear Scientist,
My Dad and I were talking about the troubles associated with the oil being 
extracted off the west coast of Africa, which led us to contemplate how 
many billions of gallons of oil have been removed from beneath the Earth.  
We then wondered - what happens to the space where the oil was?  Does 
something (water?) seep in to take its place? Is the space the oil 
occupied compressed by the mass of what lies above it?  Thanks very much 
for taking the time to consider our question.
Catherine

Re: When oil is extracted , what happens to the space that the oil occupied?