Kinetic inhibition of formation of methane hydrate (CS-I) and methane-propane (CH4 + C3H8 in 95.66 + 4.34 mole %) hydrate (CS-II) by the polymeric reagents Luvicap 55W and Luvicap EG is studied in the 40-120 bar pressure range. Cooling at the constant rate of 1A degrees C/hr was used to assess the effectiveness of kinetic inhibition. It is shown that the kinetic hydrate formation inhibitors (KHI) Luvicap 55W and Luvicap EG in identical proportion of 5000 ppm are capable of inhibiting methane hydrate formation at a supercooling temperature twice as low (6-7A degrees C) as in the case of hydrates of methane-propane mixture (13-14A degrees C). In the presence of KHI, hydrates appear in the system in the form of visually discernible opacity of the initially transparent aqueous solution at a temperature that is 1-2A degrees C higher than the temperature at the point of deviation of the P(T) curve from the straight line, i.e., they appear earlier than appearance of signs of gas absorption. Formation of such trace quantities of hydrate do not cause a marked deviation of the P(T) curve from the straight line and can be discerned only by more sensitive physicochemical methods. The inhibiting properties of Luvicap EG and Luvicap 55W with respect to methane hydrate differ insignificantly, but the former is more effective in inhibiting crystal growth. The experimental data indicate that Luvicap 55W is more effective than Luvicap EG in inhibiting nucleation and growth of methane-propane hydrate crystals.