References
- Helman, C. (2016). The World’s Biggest Oil Companies, The World’s 25 Biggest Oil Companies: forbes.com (https://www.forbes.com/sites/christopherhelman/2012/07/16/the-worlds-25-biggest-oil-companies/#70ed1d9360ca).
- Rosneft. (2015; 2014; 2013; 2012; 2011; 2010). Annual Report.
- ExxonMobil. (2015; 2014; 2013; 2012; 2011; 2010). Annual Report.
- British Petroleum. (2015; 2014; 2013; 2012; 2011; 2010). Annual Report.
- Royal Dutch Shell. (2015; 2014; 2013; 2012; 2011; 2010). Annual Report.
- Chevron. (2015; 2014; 2013; 2012; 2011; 2010). Annual Report.