Compressor, comprising a sealed outer casing, inside which is arranged a gas compression stage driven by a motor arranged inside the outer casing. The lower part of the inner casing containing the motor is sealingly closed by a bottom, and at least one vertical chimney is arranged in the annular space formed between the outer casing and the lower casing, the chimney being arranged substantially vertically along the motor and the lower casing, and communicating in its upper part with the low-pressure zone of the compressor and, in its lower part, with the inside of the lower casing, one or more openings being made between the chimney and the bottom of the motor.