Artemkina, L. R., Sopilko, N. Y., Myasnikova, O. Y., Eremina, I. U., Bondarchuk, N. V., & Shamsheev, S. V. (2019). The Model of Upstream Investment Portfolio in the Mature Regions. International Journal of Energy Economics and Policy, 9(4), 173–180. Retrieved from https://econjournals.com/index.php/ijeep/article/view/7965