Peak oil, gas, etc. are not concepts. They are basic observations or truths. If you have a glass of water and slowly pour it out, at some point you will no longer have any water. Theory? A concept? No. Fact. A fact we should all grasp soon.
The fossil fueled world we live in is nothing but a very small blip in the history of mankind. It will all be over soon. Six billion people only exist because of finite fossil fuels.