1. Birol, F. (2003). World energy investment outlook to 2030,
2. Business briefing: Exploration and production. The oil and gas review 2003 (Vol. 2).
3. Coal: Resources and future production. (2007). Background paper prepared by the Energy Watch Group March, EWG-Series No 1/2007, Ludwig-Bolkow-Foundation
4. updated version: 10th July 2007, Final-Version 28032007.
5. Coal: Secure energy. (2005). World Coal Institute: London, UK