Al-Ayed, Omar. “Catalytic Cracking of Vacuum Gas Oil and Used Lubricating Oil on Oil Shale Ash”. Global Journal of Energy Technology Research Updates 2, no. 1 (April 1, 2015): 25–32. Accessed July 26, 2024. https://avantipublishers.com/index.php/gjetru/article/view/193.