Abstract: To achieve high measurement accuracy of Coriolis-type single-tube hoop-mode mass flow sensors for nonideal fluids, such a mass flow sensor comprises a vibrating system containing a single straight measuring tube as a main vibrator and an auxiliary vibrator which does not come in contact with the fluid and is mechanically coupled to the measuring tube via connecting elements, the vibrating system being so excited in a natural frequency of vibration by means of at least one exciter that the measuring tube vibrates in a hoop mode. The mass flow sensor further comprises a support tube, to which the vibrating system is attached at the ends and via which the vibrating system is connected with a conduit, and sensors for the inlet-side and outlet-side vibrations of the measuring tube. The vibrating system is so designed that its kinetic energy is at least twice as high as that of the measuring tube.