Reply #1: They do have a submersible that will dive to the bottom

[Captain Boomerang]

of the ocean.

However, it was only attempted once (1963ish-National Geographic covered it.) And the underwater vehicle could only accommodate two people since its hull was a foot thick steel and diesel was used as some sort of weight device.

Russian nuclear subs were created to operate at a depth of 4000/5000 feet.

My concern is;
1. If the pressure is so intense that it compresses other things, does it compress something organic like oil?
2. If oil is lighter than water, how fast does the oil travel out of the hole?
3. If the hole contains pockets of air or gas (Methane) what happens when salt water rushes in to these cavities?
4. Could giant sinkholes be created from movement of fluids?
5. Has any of the oil companies ever wondered about what happens if these underground holes were to collapse on a grand scale?

Nice link. (Thanks.)