A field trial of caustic flooding is reported for a reservoir containing a 20 degrees API oil. Field data showed the process to behave qualitatively as it does in laboratory core floods. Incremental oil over waterflooding for the field trial was estimated at 350,000 STB. The caustic flood resulted in no injection or producing problems. problems. Introduction In Oct. 1966 an experimental secondary recovery project was begun in a limited portion of the existing project was begun in a limited portion of the existing second and third zones waterflood in the Whittier oil field in Whittier, Calif. The major feature of the oil recovery scheme was a caustic flood conducted in the area shown in Fig. 1 that was in the center of the field. The caustic flooding process was used because laboratory tests had indicated that a considerable increase in oil recovery would result over plain waterflooding in this field. Screening tests on many crude oils for susceptibility to caustic flooding had earlier shown that the Whittier second- and third-zone crude reacted favorably with caustic to give extremely low interfacial tensions. It was believed that these low interfacial tensions, shown in Fig. 2, would result in much improved volumetric sweep efficiencies through a mechanism of in-situ emulsification. Reservoir Description Formation A typical well log of the section including the second and third zones is shown in Fig. 3. The top of the second zone occurs at an average subsea depth of 1,500 ft and the top of the third zone is at 2,100 ft. The net oil sand in the two zones averages about 37 and 100 ft, respectively, with porosity of about 30 percent in both zones and arithmetic air permeabilities percent in both zones and arithmetic air permeabilities of 495 and 320 md, respectively. Both zones dip sharply to the south at an angle of 25 degrees to 45 degrees. A fault runs roughly east and west across the middle of the field and forms a natural barrier for the pilot area. pilot area. Reservoir Fluid The gravity of the oil averaged 20 degrees API and the viscosity at reservoir conditions of 365 psi and 120 degrees F was about 40 cp. Wells The well spacing in the 63-acre project area varied between 1 and 2 acres per well. The project began with 45 producers and four injectors in the two zones. Later problems required the conversion of one producer to injection. All of the producers in the project area were completed in both sands except for the three wells noted in Fig. 1. The four initial injectors Wells 48, 75, 157, and 135initially injected controlled amounts into each of the two test zones. The well problems mentioned earlier required shutting off Well 48 injection into the second zone, and injection from Wells 75 and 157 into the third zone. To replace this lost injection, Well 178 was converted to injection in the third zone. Reservoir Performance During Waterflood Water injection into the project area began in early 1964. P. 1353