AL-Mishaal, O.F., Hussein, A.O. and Issa, T.A. 2025. Manganese-Based Bifunctional as an Oil–Soluble Homogenous Catalyst for in–Situ Catalytic Upgrading of High Sulfur Heavy Crude Oil. Journal of Petroleum Research and Studies. 15, 4 (Dec. 2025), 127-143. DOI:https://doi.org/10.52716/jprs.v15i4.972.