Equilibrium data of ethylene sorption on activated carbon in the presence of water are measured for near-critical temperatures. The isotherms indicate the formation of hydrates. Hydrate is a compressed state of gases and receives interest in gas storage or separation, and the formation in carbon pores may reach complete conversion and show better dynamic behavior. It is presently shown that the hydrate formation pressure at above-critical temperatures observed in carbon pores is considerably less than that reported for water media. Both the molar ratio of water to ethylene at equilibrium and the ratio of formation enthalpies for sub- and supercritical temperatures indicate that the ethylene molecules cannot stay in the small cages of clathrates when the temperature increased to above critical.