OKE, D. M.; KAREEM, S. D. An Inter-temporal Analysis of Operational Efficiency of Oil Firms: Further Evidence from Nigeria. International Journal of Energy Economics and Policy, [S. l.], v. 3, n. 2, p. 178–184, 2013. Disponível em: https://econjournals.com/index.php/ijeep/article/view/421. Acesso em: 27 apr. 2024.