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This paper is a report on the conception of and resulting performance of a waterflood operation which has been carried out in the Tanjung Tiga Timur Field located in South Sumatra. The field was discovered in 1940 when well ITT-2 was drilled to a total depth of 1212 meters, As of September 1981, a total of 39 wells had been drilled.The original oil in place is 15,625,000 m3. Approximately 7,520,000 m3 are contained in the upper zones (al, ao, A,B,C)and8,105,000m3 areinthelower zones (D-H). Reservoir pressures indicate that the recovery mechanism is a strong water drive in the lower zones and solution gas drive with limited water influx in the upper zones.The upper zones in the western portion of the field are currently being waterflooded using a line drive pattern along the southern flank. Waterflooding was initiated in July 1979, with two injection weus. Three additional wells were added, and water injection will be extended into a pezipheral flood pattern, after the north side of the field has been fully delineated through further development drilling.The cumulative oil production from the waterflood zones at start up time was 902,320 m3, or 12% of the original oil in place. At the end of October 1982 the oil production was 1,028,270 m3. The cumulative water injected was recorded at the amount of 663,352 m3.The absence of a strong water drive in the upper zones, high pressure in newly drilled well TTT-96 and erratic tracer break-through indicate that the reservoir continuity may be a problem in the upper zones.In April 1982, a numerical model study using a coarse grid model was conducted. This model does not provide the flexibility needed to fully optimize waterflood recovery. ?he model indicates that 10-20 m3lday of oil is currently being lost at production wells into the a1 zone which is not receiving any injected water. Current field operation could result in an oil recovery of 1 976,500 m3 after 20 years from the upper zones since the beginning of the project, compared to 776,500 m3 calculated from decline analysis curve without flooding.