Abstract: Method for at least partially converting methane-containing gas, in particular boil-off gas, retained in a container, to a liquid state, the method comprising the subsequent steps of: feeding methane-containing gas from said container to a compressor, and increasing, by said compressor, a pressure of said fed methane-containing gas; feeding said increased pressurized methane-containing gas to a cooling unit for cooling said pressurized methane-containing gas; decreasing said pressure of said pressurized and cooled methane-containing gas, thereby obtaining methane-containing liquid and flash-off gas; feeding said methane-containing liquid and said flash-off gas to said container, wherein said flash-off gas is inputted into said container at or near a bottom part of said container for at least partly dissolving said flash-off gas into said methane-containing liquid. System for at least partially converting methane-containing gas, in particular boil-off gas, retained in a container, to a liquid state.