De Avila Arroyo, J. P., M. Yago, M. A. Nasir, and J. Wu. “Strategic Alliance in Energy Sector & Implications for Economic Growth and Technical Efficiency: The Case of Petrobras and Galp”. International Journal of Energy Economics and Policy, vol. 4, no. 4, Oct. 2014, pp. 759-71, https://www.econjournals.com/index.php/ijeep/article/view/953.