A centrifugal gas compressor fed with a gas and a processing liquid comprises a rotor rotated by a prime mover. The rotor defines an internal axial cavity with a cylindrical surface, an annular peripheral collection cavity, and a tapered radial channel fluidly connecting the internal axial cavity and the annular peripheral collection cavity. With each rotation of the rotor, a portion of the processing fluid is swept into the inlet of the tapered radial channel and travels radially as a fluid piston under centrifugal force pushing and compressing a column of gas entrained in front of said fluid piston, and is expelled into the annular peripheral collection cavity where it undergoes centrifugal separation, leaving the compressed gas to be drawn off through the compressed gas outlet for downstream use. A method for compressing a gas is also provided.