The first 250 bbls of oil with iso-propyl acetate is followed with a 750 bbl oil injection to push the ester bank away from the well about 15 to 20 feet. All the injection oil is tagged with a material balance tracer such as methyl iso-butyl ketone (MIBK). The ester tracer stays together as a donut shaped bank and is continuously in equilibrium with both the oil and water phases. This injection usually is completed in one to two days.