The Sadi reservoir is one of the largest and most important unconventional tight oil reservoirs in southern Iraq. However, it suffers from low production rates, necessitating many development strategies that require a correct and reliable characterization of reservoir fluid properties. Whilst these properties are originally obtained from laboratory experiments, measurement errors often occur despite rigorous workflows, which negatively affect the calculation of reservoir fluid properties. This study utilizes the fluid thermodynamics characterization program (PVTp) to generate a reliable model for determining the oil properties of Sadi reservoir. A methodology was developed to simulate fluid thermodynamic tests, including Differential Liberation (DL) and Constant Composition Expansion (CCE) tests. This was achieved through adjusting the Peng-Robinson Equation of State (PR-EOS) by splitting and lumping the C7+ plus fractions and calibrating the Ω parameters to match model results with experimental data using regression. Using the absolute average error (AAE) as a model performance benchmark, the model achieved an AAE of 1% for estimating the relative volume, 0% for estimating oil density, 0.41% for estimating oil formation volume factor, 4% for oil viscosity, and 5% for the gas oil ratio. These values represent the highest AAE recorded for this dataset and show good agreements within the acceptable limits. The PR-EOS model proves to be an accurate fluid characterization alternative that can be applied to similar field data, providing a valuable tool for reservoir management, improving performance, and reducing costs in the future.