Separation of complex and multicomponent fluids which consist of numerous hydrocarbon and nonhydrocarbon components is an important process in many industries including oil, gas and petrochemical industries. Considering the importance of investigating phase equilibria in processes like distillation and extraction, extensive attempts have been made to predict phase equilibria of complex systems. In order to use conventional thermodynamics, a complete chemical analysis of the complex mixture is required. Even if such analysis are available, including all components leads to massive calculations. Pseudo component and key component methods are employed to make the phase equilibria calculations of complex mixtures tractable. Recently, the continuous thermodynamics method has been used extensively. In this method, a continuous distribution function is used to represent the concentration of all existing components. The main advantage of this method is decreasing the time of computational calculations to a considerable extend. In the present research, liquid-liquid equilibria of mixtures containing hydrocarbons and methanol is investigated. The studied systems are the binary mixtures of normal paraffins-methanol and multicomponent mixture of methanol-gasoline blends. It has been verified that adding alcohol to gasoline decreases exhaust pollution, but we are confronted by the serious problem of limited liquid miscibility. Therefore it is important to determine maximum concentration of alcohol which can be added to gasoline in such a way to avoid phase separation. Due to strong hydrogen bonds in alcohol molecules, alcohols form chain associates. In order to consider dispersity of alcohol chain associates and gasoline as a complex mixture, the continuous thermodynamics approach (the CONTAS model) has been employed in this study. The calculations are based on the Unifac, the Larsen Modified Unifac and the Dortmund Modified Unifac models. In characterizing complex gasoline mixture, aromatics and naphthenes have been represented by model compounds and continuous distribution functions have been employed for paraffins. Results show that Unifac and CONTAS models are appropriate to study liquid-liquid equilibria of methanol-gasoline blends. Unifac Model is suggested to be used at low temperatures while the CONTAS model is suitable at high temperatures. At low temperatures, solubility of methanol in gasoline decreases and lower amounts of methanol can be added to gasoline. Increasing aromatics concentration in gasoline causes an increase in solubility of methanol in gasoline. Also by increasing the variance of paraffins in gasoline, the distance between cloud and shadow curves increases.