Gas hydrates are crystalline non-stoichiometric inclusion compounds, where hydrogenbonded water molecules play the host role while small molecules (methane, ethane, hydrogen sulfide, nitrogen, carbon dioxide, hydrogen, propane, isobutane, etc.) occupy the cages in the host framework [1]. Process of gas hydrate nucleation is important for understanding of their formation regularities. There is a large number of recent studies showed that the hydrate nucleation occurs on boundary of water and hydrate-forming gas (liquid containing dissolved hydrate-forming substance), or on the line of water – hydrate-forming gas – solid (as a rule, the reactor design elements) [2-4]. In the present work, kinetics of methane and methane-ethane-propane hydrates nucleation in water – organic liquid – gas systems with / without surfactants in the presence of four types of phase boundaries was studied. Sapphire Rocking Cell RCS6 with six transparent sapphire cells was used. The experiments were conducted at the constant supercooling (ΔT = 20.2°C). Decane, toluene and crude oils were used as organic liquids. It was observed that gas hydrate nucleation occurred on water – stainless steel – gas and water – sapphire – organic liquid three-phase contact lines rather than on water – gas or water – organic liquid interfaces. The empirical survival curves was constructed both for the entire set of data and for each cell separately. Hydrate nucleation in 87% of cases occurred near the contact line of the water – stainless steel – gas in experiments with pure decane and toluene. In the remaining 13% of cases, nucleation happened near the contact line of water – decane – sapphire. Two series of experiments were also conducted for the system of water – decane – Surfynol 420 – methane with the same sample. Series of experiments differed with cell angle relative to the horizontal (45 and 14°). The length of the contact line of water – decane – sapphire differ by about 1.9 times (the interface area of the water-decane by about 2.5 times). Comparison of the observed thermal effects with data of visual examination for this system allowed nucleation rates of methane hydrate to be determined on the different nucleation sites.