Othman, N., Z. Yusop, M. M. Ismail, and S. H. M. Afandi. “Energy Tax and the Downstream Palm Oil Trade Competitiveness Nexus in Malaysia: An Application of GMM Approach”. International Journal of Energy Economics and Policy, vol. 11, no. 5, Aug. 2021, pp. 593-9, https://www.econjournals.com/index.php/ijeep/article/view/11558.