This study was carried out to compare the performance of different oxidation processes, such as solar photo-Fenton reaction, solar photocatalysis by TiO2, and the combination of the two for the treatment of petroleum wastewater from Sohar Oil Refinery by a central composite design with response surface methodology. The degradation efficiency was evaluated in terms of chemical oxygen demand (COD) and total organic carbon (TOC) reductions. Solar photocatalysis by the TiO2/Fenton method improved the performance of the photocatalyst at neutral pH for petroleum wastewater without the need to adjust the pH during this treatment. Under acidic conditions, the solar photo-Fenton process is more efficient than solar TiO2 photocatalysis while it is less efficient under alkaline conditions. The TiO2 dosage and pH are the two main factors that improved the TOC and COD reductions in the solar photocatalysis using combined TiO2/Fenton and the solar TiO2 photocatalysis processes while the pH and H2O2 concentration are the two key factors that affect the solar photo-Fenton process.