It is only theoretical to those that wish for a magic method of earth pumping out oil without regard to the laws of physics. Those that actually have to produce oil & gas for a living instead of just talk about it usually understand. We don't just drill anywhere and hope; there is plenty of sciences in searching for petroleum.
How detailed do you want to go?
This?
http://www.eia.gov/kids/energy.cfm?page=oil_home-basics
Or this?
http://www.petroleumgeology.org/sedstrat.cfm
Do you understand how sedimentary rock is formed and why it is different from igneous rock? This is a very basic part of understanding the formation of petroleum fields.
“Do you understand how sedimentary rock is formed and why it is different from igneous rock?”
I had a graduate level course in historical geology (although I was an undergrad at the time) from Prof Loudon, U. of Wis.-Madison, and a course in glacial geology (same institution), and hold a doctorate in soil science.
But I do not know how petroleum is formed, and do not know whether anyone does, there not having been any witnesses to the phenomenon in action, but surely the inquiring mind of curious man has conjured theories as to how this might have occurred, and written books and learned essays about their conclusions.
No one here knows? Very well, there’s always Google.