In this paper, advanced oxidation process (AOP) combining ultrasound (US) and Fenton's process was proposed for the treatment of total petroleum hydrocarbons present in oil spill sludge. The effect of several parameters like pH, ultrasonic power, weight ratio of hydrogen peroxide to iron [H2O2/Fe2+], Fenton reagent dosage, addition of salts and contact time were analyzed for the reduction of Petroleum Hydrocarbons (PHCs) in terms of hydrocarbon fractions (nC7–C10, nC11-C20). Chemical characterization of oil spill sludge was analysed by gas chromatography- mass spectrum (GC–MS) Elemental analyser, Fourier Transform Infra Red (FT-IR) Analyser and particle size analyser. Experiments were conducted for identifying the wide range of hydrocarbons fractions (nC7–C10, nC11–C20 and nC21–C30). Results shown that maximum solubilisation and PHC removal rate of up to 84.25% could be achieved at a pH of 3.0, sludge/water ratio of 1:100, ultrasonic power of 100 W with 40–50% ultrasonic amplitude, a H2O2/Fe2+ weight ratio of 10:1, and an ultrasonic treatment time of 10 min. The lower and medium fractions (nC7–C10, nC11–C20) were amenable to degradation due to ultrasound treatment compared to the heavier carbon fraction (nC21–C30). The study concludes that the combined sono-Fenton (SF) process significantly enhanced the degradation of oil spill sludge as compared to ultrasound treatment and Fenton oxidation alone. The enhanced solubilisation achieved by US alone is highly beneficial when we couple this with biodegradation which will be greatly facilitated by the enhanced solubility. © 2018 Elsevier B.V.