Abstract: The yield and the reservoir capacity of River Owena in Ondo State were estimated using a combination of the Rippl`s mass curve and the Loucks Sequent Peak Procedure. The yield was found to be 299.99x106m3. However, the reservoir capacity obtained from the mass curve was 125x106m3. This is lower than the yield value and if used for the dam design, there will be a danger of the reservoir capacity not being able to meet the expected demand. Further analysis was done using the Loucks Sequent Peak Procedure. The value from this procedure was 3.30x109m3. This capacity is safe and reliable and will ultimately meet the water demand of the people in the coverage area.