Offshore oil production, which is a significant source of petroleum, has recently caused extensive concern. Produced water (PW) is the highest-volume byproduct of oil and gas production. The organic pollutants dominated by hydrocarbons, namely oil, in PW are the major concerns to researchers because of the adverse effects to the marine ecosystem. In industrial processes, the oil is needed to be separated by individual or cooperative use of separation technologies, such as gravity settlement, enhanced gravity settlement, and hydrocyclones. However, these conventional technologies cannot reach the separation requirements in a compact space under extreme conditions, such as emulsification and large volumes of PW. To improve the treatment efficiency, decrease the occupation of space, the practical use of a full-scale PW treatment process was proposed and investigated in the Bohai Sea, China. The oil content of PW after treatment with the full-scale process was less than 20 mg·L-1, alongside a reduction in the chemical dosage concentration (over 40% and 60% for reverse demulsifier and water clarifier, respectively) compared with the conventional process. Besides, an increase in the amount of produced liquid and PW of over 50% and 40% was achieved, respectively, generating a 30000 m3·a-1 growth in oil production in this single wellhead platform. The organic compounds and relative concentrations of these compounds were analyzed in this full-scale practical application. Hydrocarbons were the major organic pollutants in PW. Approximately 100 kinds of organic compounds that were detected in the influent of the process were reduced to 8 in the effluent with a separation efficiency over 90%, which made the PW cleaner to the marine environment. The simultaneous separation of alkanes and slightly soluble organics in PW can be explained by rotation and internal circulation, which provides a possible mechanism by which slightly soluble materials in major phase could be transferred from major phase to dispersed phased, in which the materials have a significantly higher solubility. This study provided an attractive strategy to answer the ecological menace caused by the hydrocarbon exploitation in offshore oilfields, to the benefit of both the economy and the environment. Display omitted •An industrial full-scale practice of an offshore platform was investigated.•Organic characteristics of PW were systematically analyzed.•Organic pollutants in PW were dominated by hydrocarbons.•Alkanes and soluble organics can be separated simultaneously.