Oke, David Mautin, and Salami Dada Kareem. “An Inter-Temporal Analysis of Operational Efficiency of Oil Firms: Further Evidence from Nigeria”. International Journal of Energy Economics and Policy 3, no. 2 (April 3, 2013): 178–184. Accessed April 28, 2024. https://econjournals.com/index.php/ijeep/article/view/421.