The conditions at which methane and water form solid hydrates have beenextended from 4,000 to 11,200 pounds per sq. in. The curve at high pressure hadbeen in doubt because of Villard's report of a critical decompositiontemperature. The paper explains the nature of the hydrate curve at highpressure and its dependence on fluid phase behavior. Extropolation of themethane hydrate curve indicates a pressure of 40,000 pounds per sq. in. willcause hydrates to form at a temperature of 100' F. Introduction The conditions under which natural gases form hydrates when liquid water ispresent have been studied by several investigators up to pressures of about4,000 pounds per sq. in. The early work by Villard on hydrates of methane andethylene, ethane, and propane included references to critical decompositiontemperatures of the hydrates. Villard's work raised the question as to whetherthe pressure-temperature curve for methane-water hydrate continued above atemperature of 70.7?F. or whether this was the maximum temperature at whichhydrates would form. This paper extends the experimental data on methane hydrate to 11,200 poundsper sq. in. A discussion of phase relations in the hydrate region for thehydrocarbons and of the methane-water system at high pressures isincluded. Previous Work Villard suspected that methane hydrates could not be formed at temperaturesabove 21.5?C. (70.7?F.) irrespective of the pressure of the liquid-vaporsystem. However, he was limited in his studies by his apparatus in 1888 topressures not greater than 300 atmospheres (4,410 pounds per sq. in.) so thatthere has remained some doubt as to the existence of such a maximum temperaturein this region. For the case of ethylene hydrates, however, Villard does specifically state theoccurrence of what he terms a "critical temperature for the decompositionof the hydrates." T.P. 2579