Subsea centrifugal compressor unit, comprising: - a motor having a rotor, - at least one compressor having a shaft driven by the rotor; and - a set of bladed wheels fitted on the driven shaft, said motor and said compressor being mounted in a common watertight casing comprising a first casing element accommodating the motor and a second casing element accommodating the compressor, and further be provided with cooling means for cooling the motor and bearings of the subsea centrifugal compressor unit, wherein, in operation, the motor, the compressor and the casing having the motor and the compressor are arranged horizontally, and the compressor unit further comprises one axial thrust bearing only on a compressor side, wherein the said cooling means are arranged as an open loop including a clean gas supply entering the first casing element at one side of the rotor opposite of the compressor, an additional bladed wheel provided on the rotor for directing the clean gas supply to the motor, through a first radial bearing supporting an end of the rotor and to the compressor through a seal of the subsea centrifugal compressor unit, the seal being between the motor, downstream the cooling means, and the compressor. - a motor having a rotor, - at least one compressor having a shaft driven by the rotor; and - a set of bladed wheels fitted on the driven shaft, said motor and said compressor being mounted in a common watertight casing comprising a first casing element accommodating the motor and a second casing element accommodating the compressor, and further be provided with cooling means for cooling the motor and bearings of the subsea centrifugal compressor unit, wherein, in operation, the motor, the compressor and the casing having the motor and the compressor are arranged horizontally, and the compressor unit further comprises one axial thrust bearing only on a compressor side, wherein the said cooling means are arranged as an open loop including a clean gas supply entering the first casing element at one side of the rotor opposite of the compressor, an additional bladed wheel provided on the rotor for directing the clean gas supply to the motor, through a first radial bearing supporting an end of the rotor and to the compressor through a seal of the subsea centrifugal compressor unit, the seal being between the motor, downstream the cooling means, and the compressor. said motor and said compressor being mounted in a common watertight casing comprising a first casing element accommodating the motor and a second casing element accommodating the compressor, and further be provided with cooling means for cooling the motor and bearings of the subsea centrifugal compressor unit, wherein, in operation, the motor, the compressor and the casing having the motor and the compressor are arranged horizontally, and the compressor unit further comprises one axial thrust bearing only on a compressor side, wherein the said cooling means are arranged as an open loop including a clean gas supply entering the first casing element at one side of the rotor opposite of the compressor, an additional bladed wheel provided on the rotor for directing the clean gas supply to the motor, through a first radial bearing supporting an end of the rotor and to the compressor through a seal of the subsea centrifugal compressor unit, the seal being between the motor, downstream the cooling means, and the compressor.