system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is left behind underground after oil companies pump billions of gallons of oil out of a reserve?

Is it a giant cavern? Will the Earth's crust be in danger of collapsing when we're finished pumping?
gpt
At first the oil is under the pressure of all the rock above it pressing down.  That's how you get the iconic gushers you see in movies.  The cavern doesn't empty at that point, it is combination of the oil expand as pressure is relieved, and the rock around it deforming.

After that, the best way to get the oil out is to pump water down to force it back up.

> Will the Earth's crust be in danger of collapsing when we're finished pumping?

No, the total volume of oil is minuscule compare to the entire crust.  It is possible for those changes to create local seismic activity.