An extrapolation of parameters from an experimental study of CO2-hydrate nucleation in porous media is used to describe the nucleation of CH4 hydrate under conditions found below the seafloor. The requirements for nucleation can significantly delay the onset of hydrate formation when CH4-bearing liquids rise into the hydrate stability zone. Hydrate may not form at all if the vertical extent of the stability zone is too narrow to achieve sufficient cooling below equilibrium temperature. This is particular relevent in shallow water or at times in the Earth's past where the ocean floor was warmer than today.