Yeah, when you think about it the global volume of oil is actually not that big after all. If we assume 2,000 billion Bbls as the absolut global reserve and imagine it is equally spread on the serface of the Earth, then it will only be a 0.6 mm thick layer, just like a very thin layer of paint.

I'm not so persuaded of this notion that people will still go on burning/using coal. You can't just dig it up with a spade in your garden. You have to (1) go to the remote location, (2) use some heavy machine to break it up and get it out (or seriously heavy manual labour); you then have to haul it back to its place of use. All this requires time, energy, steel etc. We might not have these available in sufficient quantity and cheapness to be able to do that coal-digging. I'm more fearful of all the trees getting burned to extinction by people trying to keep warm and well-fed.