Polymer enhanced oil recovery (EOR) operation has been implemented for the production of oil from difficult mature oilfields in Oman. The polymer used in this EOR technique to sweep oil toward production wells is resulting in the generation of polymer flood produced water (PFPW) of increasing viscosity. Current methods of treating oilfield produced water must be reconsidered for the effective treatment of such PFPW of changing quality. In a previous study, the utilization of polyaluminum chloride (PAC) chemical was proposed for the coagulation of oil in produced water to be separated by flotation and filtration. As such, laboratory tests were conducted to evaluate the applicability of PAC and other chemicals for treatment of PFPW that has higher viscosity than ordinary oilfield produced water. These tests clearly indicated that aluminum sulfate (AS) chemical was more effective for treatment of such higher viscosity water. A pilot plant developed during the earlier study, was utilized to conduct coagulation/flocculation, flotation, filtration, and adsorption treatment trials for PFPW from an oilfield where polymer EOR is underway. For the final trial, the inlet PFPW viscosity was 1.4 cP at 40 °C and oil concentration was above 200 mg-L-1. AS was applied for coagulation/flocculation and flotation stages, and was found to be effective in reducing oil concentration to 1 mg-L-1. Filtration and adsorption stages resulted in further improvement of water quality. Most of the polymer used for EOR was believed to have been removed along with oil and suspended solids.