Frequently there is a necessity for prevention of gas hydrate solid phase appearance in gas treatment systems, for instance, at gas-condensate preparation plants of Russian northern gas-condensate fields. The injection of methanol or glycols is commonly used for such purpose. In this work, technological schemes of gas treatment where injected methanol is used for hydrate control are considered. A simple, but realible method for thermodynamic calculations of the hydrate inhibition process during gas treatment is presented. In this connection, a simplified approach for calculation of VLH phase equilibria in gas-condensate stream is discussed. Some new experimental data for VLH equilibria are presented, where V - is three-component gas phase (mixture of CH4+C2H6+C3H8, which models the composition of natural gas in gas-condensate fields); L - liquid water phase (the solution 'water plas methanol' in which CH3OH has more than 50 wt%); H ⇔ hydrate phase. Computer programms are developed for calculating the optimal inhibitor amount for a gas and gas-condensate preparation plant upstream from a transport pipeline.