Treatment technologies for reclaiming oil field produced water for beneficial reuse were evaluated, including thermal and membrane processes for salinity removal. Warm precipitative softening and high-pH reverse osmosis were selected for pilot testing based on a literature review of treatment technologies and results from bench-scale softening tests that indicated hardness, boron and silica removal could be simultaneously optimized. Introduction The goal of this project is to convert a currently unusable byproduct of oil production, produced water, into a valuable drinking water resource. To accomplish the project goal, the project team has built a pilot plant to treat oil field produced water to current and anticipated California potable and reuse water standards. The project site is the Placerita Oil Field which is located in the County of Los Angeles near the City of Santa Clarita, California. The project is divided into two phases: Phase I (research and planning) and Phase II (pilot testing). This paper summarizes the results of Phase I, including a literature-based review of treatment technologies applicable for produced water, planning level cost estimates of recommended technologies, and results from bench-scale precipitation studies. The paper also identifies the treatment train that is currently being tested as part of Phase II of this project. The paper was adapted from Ref. 1, which provides a more detailed summary of this project. Several entities with diverse interests are contributing funds to this project. They include the U.S. Department of Energy, ARCO Western Energy, a wholly owned subsidiary of Atlantic Richfield Company, Castaic Lake Water Agency, Electric Power Research Institute Chemicals and Petroleum Office, Southern California Edison, the National Water Research Institute and Kennedy/Jenks Consultants. The diverse sources of funding for the project reflect the wide range of potential beneficiaries that have an interest in the success of the project, including:Oil companies that dispose of the produced water through costly underground injection at high pressures;Oil refineries that may be able to use these technologies to recycle water at their facilities;Water utilities that need additional water resources and are located near a producing oil field;Water users with projects such as housing developments and industrial manufacturing complexes that require additional potable water resources before they can build their projects. Project Approach This project is structured to solicit input from members of the drinking water treatment and reclamation community, including staff of state regulatory agencies. The approach is intended to identify and address concerns early enough to obtain agency approval of the proof of concept process train similar to the wastewater reclamation reuse regulations in California's Title 22. The result would be a set of guidelines and design criteria that are applicable throughout California for reclaiming produced water, substantially decreasing the cost of future produced water reclamation projects. If the project obtains Department of Health Services approval, a 43,000 barrel per day [1.8 million gallon per day (mgd)] treatment plant may be built in Santa Clarita, California. P. 811^