Oil exploration and production in the Sultanate of Oman is associated with many challenges, of which the disposal of 600,000 m3d -I of oil production water in environmentally sound method is of foremost importance. This water is contaminated with petroleum hydrocarbons, traces of phenols, emulsifiers, a wide range of metals and has an electrical conductivity of 12 dS m-I. This study evaluated the use of Nimr reed bed technology for treating oil production water and the role of its associated chemical and biological processes in the contaminant removal. The combined interactions between the substrate, macrophytes and the inhabiting microorganisms resulted in considerable reductions in the inorganic and organic contaminants simultaneously. Metals in the effluents were reduced by 78% for (AI, Ba, Cr, Cu, Zn & Li), up to 40 for Fe, Li, Mn, Pb and appreciable reductions of As, Cd, Co, Mo, Ni, Se, TI and V. A much better and consistent reductions were achieved total hydrocarbons averaging 96% for the three years of operation. The contaminants were virtually eliminated within the primary reed bed by aerobic and to a lesser extent by anaerobic processes. Metals were adsorbed by clays, chemisorbed by oxides. precipitated as metalcarbonates and sulphates, organically complexed. precipitated as metal sulphides and absorbed into primary and secondary minerals. After the first year, reeds became mature and started taking up and accumulating significant quantities of metals, which virtually eliminated any further accumulation in the substrate. Hydrocarbons were predominantly attenuated by the developed sediment layer and creeping on reeds accommodating as much as 36±9 and 43±13% of their weight oil, respectively. The dissipation of hydrocarbons was shown to being rapid and faster for the lower molecular weight compounds than the larger ones, through volatilisation, photooxidation, aerobic and to less extent anaerobic biodegradation. The adapted and acclimated indigenous microbes tolerate high salinities; biodegraded hydrocarbon loads up to 9% and tolerates the diverse range of metals at different concentrations. The clogging problem in Nimr reduced the treatment capacity from 1500 to 400 m3d-1 however. this drawback was successfully surmounted in pot experiments using a sandy loam instead of Nimr loamy soil, and surface instead of subsurface flow regime. It was concluded that the technology is viable for this application and recommendations for future work were accordingly suggested.