Petroleum refinery effluents (PREs) are wastewaters characterised by high values of chemical oxygen demand (COD) and total organic carbon (TOC). Mineralisation of PRE is not commonly reported. For Fenton oxidation, in particular, reported PRE mineralisation is low. In this paper, treatability of a petroleum refinery effluent using a Fenton-like oxidative reaction is described. A statistically designed experimental matrix was used to evaluate the individual and combined effects of process variables based on a five-level central composite design (CCD). Response surface methodology (RSM) was employed to optimise the parameters of interest (COD and TOC), and response surface equations were subsequently developed. These parameters were optimised from studies of the independent variables, for reaction time [t(r)] = 30-240 mm, molar ratio of hydrogen peroxide to the organic wastewater [H2O2]:[PRE] = 2-12 and mass ratio of hydrogen peroxide to catalyst [H2O2]:[Fe3+] = 5-20. The COD and TOC of the PRE at an initial pH of 7 were 1343 mg O-2/L and 398 mg C/L, respectively. Under optimal conditions, maximal TOC and COD reduction achieved within 30 min of oxidation reaction were 70% and 98.1%, respectively. The obtained models had correlation coefficients (R-2 and R-adj(2)) of 0.9984 and 0.9916 for TOC and 0.9636 and 0.8835 for COD. At a pH of 3, corresponding optimal oxidation conditions were found to be [H2O2] = 1008.0 mM and [Fe3+] = 686.0 mg, that is, a molar ratio of [H2O2]:[PRE] = 12 and mass ratio of [H2O2]:[Fe3+] = 5. (C) 2011 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.