Methane hydrates are restricted to the shallow lithosphere (i.e. < 2000 m depth). Necessary conditions are found only either in polar continental sedimentary rocks where surface temperatures are less than 0 °C; or in oceanic sediment at water depths greater than 300 m where the bottom water temperature is around 2 °C.
In addition, deep lakes may host gas hydrates as well. Continental deposits have been located in Siberia and Alaska in sandstone and siltstone beds at less than 800 m depth. Oceanic deposits seem to be widespread in the continental shelf and can occur within the sediments at depth or close to the sediment-water interface. They may cap even larger deposits of gaseous methane.