We present a continuous thermodynamic framework which utilizes the Flory-Huggins theory for calculating sol-gel phase equilibrium properties of polydisperse petroleum resins. The sample resins are separated into sol and gel phases by n-hexane at 10-30℃ for 5-12 hours. The molecular weight distributions for feed resin and subsequently separated sol and gel phases are determined by gel-permeation chromatograph and they are correlated by the gamma distribution function. The equilibrium distribution coefficients between sol and gel phases are modeled by the modified Flory-Huggins equation in which the mole fractions are replaced by a continuous distribution variable index. We found that the Flory-Huggins model with the continuous thermodynamic frame-work fits the measured sol-gel phase equilibrium data well for a wide range of separation conditions.