Kirichenko, O. S., A. A. Komzolov, Y. A. Nazarova, N. S. Shcherbakova, and T. V. Kirichenko. “Diversification of Russian Oil and Gas Upstream Companies”. International Journal of Energy Economics and Policy, vol. 10, no. 3, Mar. 2020, pp. 112-8, https://econjournals.com/index.php/ijeep/article/view/9194.