Lawal, Adedoyin Isola, Abiola A. Babajide, Tony Ikechukwu Nwanji, and Damilola Eluyela. 2018. “Are Oil Prices Mean Reverting? Evidence from Unit Root Tests With Sharp and Smooth Breaks”. International Journal of Energy Economics and Policy 8 (6):292-98. https://econjournals.org.tr/index.php/ijeep/article/view/6980.