Запухляк, І. Б. “Theoretical and Applied Aspects of of Forming of Value Chain of Gas Transportation Services in System of Support of Its Competitiveness”. 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. 11, Oct. 2015, pp. 10-14, https://eung.nung.edu.ua/index.php/ecom/article/view/135.