1. British Petroleum Statistical Review of World Energy. www.bp.com, June 2012.
2. World Steel Association, Steel Production. www.worldsteel.org, 2011.
3. CRU Monitor-Aluminum World Production. www.crugroup.com, 2011.
4. Copper World Production. www.en.wikipedia.org, 2011.
5. International Lead Zinc Study Group, Lead and Zinc Statistics. www.ilzsg.org.