He's trying, and failing. I'm failing, too, and I've tried the OECD and World Bank.
This is a tough search, man. Most of what I've found separates mineral extraction from energy extraction. I'd try looking on a journal database at your school; many of those need subscriptions online.
If your school has a proxy server for it's online collection, that would be a good start you can do in your pyjamas.
You may need to do some math for this one.
Edit: What is it exactly that you are looking for?