Extensive laboratory flood tests have been conducted to optimize oil recovery with micellar slugs. A study was made of the effects of variables such as temperature, crude oil type, rock type, and surfactant-cosurfactant type, and of the effects of concentration and salinity of connate water, micellar slug, and chase water. The tests demonstrated conclusively that a pronounced benefit in oil recovery can be achieved by using a particular sequence of injected water compositions. For example, it was found that optimum oil recoveries are obtained if the micellar slug contains sufficient salt to produce effective miscibility or very low interfacial tension between the micellar slug and the oil and if the water injected immediately ahead of the micellar slug has approximately the same salt content as the slug itself. It was also found that the polymer drive water behind the micellar slug should be fresh water if optimum oil recovery is to be achieved. The effect of the salinity sequence is illustrated by data obtained in floods of a Wyoming crude oil from 4-ft Berea cores at 110 degrees F. The cores were saturated with water, driven to connate water saturation, waterflooded, and subsequently flooded with 10 percent PV water-external micellar slugs (92 percent water). PV water-external micellar slugs (92 percent water). The micellar slugs were driven with a 750-ppm solution of biopolymer to achieve mobility control. The flood rate for the micellar and polymer slugs was 2 ft/D. All flooding fluids were prepared with a "fresh water" of about 2,800 ppm total solids. Sodium chloride was added in preparing the saline waters and micellar fluid. Repeat tests established that the reproducibility of the data was 3 percent in residual oil saturation after the micellar-polymer injection. Curve 1 of Fig. 1 shows the oil fraction produced during a tertiary micellar flood when a preflush (waterflood) of the same salinity (16,000 ppm) as the micellar slug is employed. Curve 2 shows the oil fraction when fresh water precedes the micellar slug. The total oil recovery, both secondary and tertiary, with the saline water preflush was 95.7 percent of the original oil in place, whereas without the saline preflush the oil recovery was 74 percent. preflush the oil recovery was 74 percent. JPT P. 957