A petroleum refinery facility discharge wastewater with average influent COD concentration of approximately 500-750 mg/L during the period of this study. Study on the treatability of the petroleum refinery effluent wastewater was conducted using bench scale biological sequencing batch reactor systems. Six sequencing batch reactors (SBR) each of 2L liquid volume were operated at a 24 hours cycle. The SBRs were operated in various anaerobically stirred and aerobic modes. The average COD removals percentages for the aerobic reactor, combined anaerobic-aerobic reactors and aerobic mixed with domestic wastewater were found to be approximately, 91, 91, and 88 respectively, with its final average effluent COD of 63 mg/L, 65 mg/L, and 44 mg/L, respectively. © 2011 WIT Press.