Sergeev, Alexandr. “KEY ASPECTS OF ECONOMIC EFFICIENCY AND COST OF NATURAL GAS PIPELINE TRANSPORTATION”. Scientific Bulletin of Ivano-Frankivsk National Technical University of Oil and Gas (Series: Economics and Management in the Oil and Gas Industry), vol. 1, no. 7, May 2018, pp. 36-42, https://eung.nung.edu.ua/index.php/ecom/article/view/93.