An experimental study and thermodynamic modeling was conducted to quantify the phase behavior and physical properties of an Iranian crude oil sample. The oil sample was compositionally characterized by the distillation technique. Also, differential liberation tests and flash were conducted on an oil sample. Experiment results for phase behavior and reservoir fluid properties were used to evaluate the reliabilities of three cubic equations of state, including Peng-Robinson, Pate-Teja, and Soave-Redlich-Kwong for predicting flash calculation, and differential liberation test simulation of Iranian crude oil. Results show that heavy components in the petroleum mixtures based on the comparisons with the experimental data have the strongest effect on the characteristics of the fluids. It is obvious that Pate-Teja equation is superior in the calculations composition gas phase in higher pressure. Also, flash calculations based on Pate-Teja equation in the case of lumping is more accurate than results obtained by Peng-Robinson and Soave-Redlich-Kwong equations. Comparison of predicted oil specific gravity, gas oil ratio, relative volume, and compressibility factor of the liberated gas based on Pate-Teja equation to experimental data shows a better agreement than other equations. It should be noted that modeling of the gas oil ratio and relative volume has better agreement with experimental data in higher pressure.