How long do you expect it to be before all fossil fuels completely run out??

Question: How long do you expect it to be before all fossil fuels completely run out??
- Keywords:
  fossil fuel
Asked by Tillie to Saiful, Petra, Jenny, Jawwad, Iain, Bethan on 18 Jan 2017.
- Bethan Charles answered on 18 Jan 2017:
  
  This is a really difficult question to answer because no one knows exactly how much is left. There may be large reserves of coal or oil or gas that we don’t know about that could last us decades. Or we could develop new technologies that help us get at fossil fuels we found it difficult to before (fracking is an example of this).
  
  However I personally hope we will transfer mainly to renewable or other clean forms of energy production long before we run out of fossil fuels.

Question: How long do you expect it to be before all fossil fuels completely run out??