The sludge from petroleum refineries and industries contains organic matter, phenols and aromatic compounds along with oily contaminants. The conventional treatment of refinery waste includes primary treatment aimed at removing the contaminants by physical treatment, followed by secondary biological treatments. The removal of contaminants needs specific treatment for specific compounds or pollutants. Separation and recovery of oil from sludge can make the process cost effective and more attractive in terms of economy of treatment. The present review briefly summarizes studies and research on petroleum oil sludge and wastewater treatment with emphasis on oil separation from sludge.