Cayon, E., N. A. Garzon, and J. S. Perez. “The Effects of Global, Regional, and Local Macroeconomic Events on the Price of the Colombian Castilla Blend”. International Journal of Energy Economics and Policy, vol. 9, no. 6, Oct. 2019, pp. 118-23, https://www.econjournals.com/index.php/ijeep/article/view/8220.