Oke, D. M. and Kareem, S. D. (2013) “An Inter-temporal Analysis of Operational Efficiency of Oil Firms: Further Evidence from Nigeria”, International Journal of Energy Economics and Policy, 3(2), pp. 178–184. Available at: https://econjournals.com/index.php/ijeep/article/view/421 (Accessed: 27 April 2024).