ABSTRACT In 1992, PT Caltex Pacific Indonesia oil field operations in Sumatra resulted in 680,000 barrels of oil produced daily and 4,600,000 barrels of slightly brackish produced water. This paper discusses the systems in operation to separate oil, gas and water to provide oil for export, gas for power generation and water for reuse and return to the environment. The systems operate quite effectively now and under normal operating conditions the water produced remains within the MIGAS Guidelines and the Pertamina/CPI goals of 25 ppm oil content and temperature of 45 °C in order to protect the environment. However, increasing production and maturation of the fields mean that there is an ever increasing amount of produced water to treat and that will require continuing efforts to maintain quality.