We studied the YSL oil field in Daqing, China with reservoir permeability 10(-3) mu m(2) that has been developed by water flooding. From the results of a preliminary estimate of the optimal injected water to oil production ratio (the injection/production ratio, IPR) and the oil-to-water ratio, we have developed a geological model that we have used as the basis for numerical simulation to determine the exact values of the indicated ratios. We propose a water flooding policy for the studied oil field.