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; characterised in that said method further comprises the step of: - exchanging heat in a heat exchanger via said heat exchanger between said methane-containing gas and said methane-containing liquid and said flash-off gas, wherein said methane-containing gas is fed to said heat exchanger before said step of feeding said methane-containing gas to said compressor, and wherein said methane-containing liquid and said flash-off gas are fed to said heat exchanger before said step of feeding said methane-containing liquid and said flash-off gas to said container; and/or - exchanging heat in a yet further heat exchanger via said yet further heat exchanger between said methane-containing gas and said pressurized and cooled methane-containing gas, wherein said methane-containing gas is fed to said yet further heat exchanger before said step of feeding said methane-containing gas to said compressor. - 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; characterised in that said method further comprises the step of: - exchanging heat in a heat exchanger via said heat exchanger between said methane-containing gas and said methane-containing liquid and said flash-off gas, wherein said methane-containing gas is fed to said heat exchanger before said step of feeding said methane-containing gas to said compressor, and wherein said methane-containing liquid and said flash-off gas are fed to said heat exchanger before said step of feeding said methane-containing liquid and said flash-off gas to said container; and/or - exchanging heat in a yet further heat exchanger via said yet further heat exchanger between said methane-containing gas and said pressurized and cooled methane-containing gas, wherein said methane-containing gas is fed to said yet further heat exchanger before said step of feeding said methane-containing gas to said compressor. - exchanging heat in a heat exchanger via said heat exchanger between said methane-containing gas and said methane-containing liquid and said flash-off gas, wherein said methane-containing gas is fed to said heat exchanger before said step of feeding said methane-containing gas to said compressor, and wherein said methane-containing liquid and said flash-off gas are fed to said heat exchanger before said step of feeding said methane-containing liquid and said flash-off gas to said container; and/or - exchanging heat in a yet further heat exchanger via said yet further heat exchanger between said methane-containing gas and said pressurized and cooled methane-containing gas, wherein said methane-containing gas is fed to said yet further heat exchanger before said step of feeding said methane-containing gas to said compressor.