A system for cooling a gas includes a pre-cool heat exchanger and a liquefaction heat exchanger. The pre-cool heat exchanger uses a pre-cool refrigerant to pre-cool a feed gas stream prior to the stream being directed to a liquefaction heat exchanger. The liquefaction heat exchanger uses a mixed refrigerant to further cool the pre-cooled gas. The pre-cool heat exchanger also pre-cools the liquefaction mixed refrigerant used by the liquefaction heat exchanger.

The present invention relates to an apparatus for transferring a fluid, particularly CO.sub.2, from a subcritical gaseous state into a supercritical state, the apparatus comprising a compressor unit, a pump unit, a drive unit and a liquefaction unit, wherein the compressor unit and the pump unit are commonly driven by the drive unit, and wherein the liquefaction unit is provided downstream of the compressor unit and upstream of the pump unit, wherein the compressor unit is configured to compress the fluid from a first subcritical gaseous state to a first predetermined pressure level of a second subcritical gaseous state, wherein the liquefaction unit is configured to reduce the temperature of the compressed fluid in the second subcritical state downstream of the compressor unit to a predetermined temperature level such that the fluid is transferred from the second subcritical gaseous state to a liquid state.