Crude oil mixture extracted from the underground; contains water, gas and solid particles, and this mixture firstly separated by a process described in the literature as 1st Process, from gases and most of the solid particles. The separated water containing 5-10% crude oil is subjected to the 2nd Process and 95-99% of water is separated. In this study, the 2nd Process was carried out with an apparatus designed using corrugated plates for crude oil-water mixtures with different properties obtained from 3 different oil production fields. In the designed setup, variable parameters such as the ratio of the distances between plates to width (0.02, 0.05, 0.07), length to width ratio (0.8, 1.2, 1.6), the temperature values of the mixture before entering the separation system (25, 30, 35 degrees C) and the mounting angles of these plates in the separation system (0 degrees, 20 degrees, 40 degrees) which affect the separation efficiency discussed. The Response Surface Method was used to obtain the levels at which the process variables have the desired effect on the response of the separation system. A maximum separation efficiency value of 99.6% was obtained at the system from the oil-water mixture pumped into the system with a fixed flow of 28 L/min.