Pray to find oil

No, by law you only own a few feet down

Depending where, it's usually 6" to 12".

You can own the mineral rights to land as well, which means you do own it very deep. Most of that is all in old trusts and not for sale without permission of the government, I think.

it depends what's under the surface

It depends on your countries laws, where I live only the top but you can still plant things if you have a farm