Evaluation of reservoir performance for petroleum reservoirs require accurate knowledge of the volumetric behavior of hydrocarbon mixtures, both liquid and gaseous. Prior to the evaluation of reservoir performance, coefficient of Isothermal oil compressibility is required in transient fluid flow problems, extension of fluid properties from values at the bubble point pressure to lower pressures of interest and in material balance calculations. The coefficient of isothermal oil compressibility is a measure of the fractional change in volume as pressure is changed at constant temperature. It is usually obtained from reservoir fluid analysis. Reservoir fluid sampling and analysis is often expensive and time consuming operation that cannot be carried out whenever the volumetric properties of reservoir fluids are needed. Hence, engineers resort to correlations developed for estimating fluid properties including the coefficient of isothermal oil compressibility. In this project, a new mathematical model for estimating the coefficient of isothermal oil compressibility based on Soave Redlich Kwong equation of state (EOS) was developed and an Excel based program. Data from four fields were used as case study and the results obtained showed that the new coefficient of isothermal oil compressibility matches closely with the experimentally values. Also, the new correlation was validated with other models and gave the least average absolute relative error range of 2.45 - 5.19 while that of Soave Redlich Kwong EOS is between 21.2 – 27. 7 and Peng Robinson EOS is between 11.8 – 16.5.