The internal pressure of liquids Ar, Kr, Xe, N-2, CCl4, CH4, n-C5H12 , neopentane, n-C6H12, cyclohexane, benzene, toluene and n-C8H18 at different temperatures and pressures has been computed using a statistical mechanical equation of state. The results have been compared to the best available experimental values. There exists a close agreement between the computed and experimental values. The temperature dependence and pressure dependence of internal pressure have been also investigated.