Procedure for determining a physical parameter of a gas using a sensor with at least a measuring tube designed to conduct the medium, wherein the measuring tube has an end section on the inlet side and an end section on the outlet side, wherein the sensor has at least a fixing unit on the inlet side and a fixing unit on the outlet side with which the measuring tube is fixed, respectively, in one of the end sections, wherein the measuring tube between the two fixing units can be excited to perform flexural vibrations of different modes with different natural frequencies, wherein of said modes a mode f1 does not have any vibration node between the fixing units, and wherein a mode f3 has two vibration nodes between the fixing units, wherein the procedure comprises the following steps: Determination of the natural frequency of mode f1 and of mode f3; Determination of a first provisional density value for the gas conducted through the measuring tube on the basis of the natural frequency of mode f1; Determination of a second provisional density value for the gas conducted through the measuring tube on the basis of the natural frequency of mode f3; Determination of a value for the sound velocity of the gas conducted through the measuring tube, and of at least a corrective term, which depends on the sound velocity and the natural frequency of a mode, for the provisional density value, which has been determined on the basis of the natural frequency of the mode, for the purpose of determining a corrected density measured value; wherein the corrective term K i for the provisional density values ρ i on the basis of the natural frequency of the mode f i has the following format: K i: = 1 + r g ⋅ c f i 2 − b, with ρ corr ⋅ = ρ i K i where rand g are constants that are independent of gas, c is the sound velocity of the gas, f i is the natural frequency of the mode f i, ρ corr is the corrected density and b is a scaling constant. wherein the measuring tube has an end section on the inlet side and an end section on the outlet side, wherein the sensor has at least a fixing unit on the inlet side and a fixing unit on the outlet side with which the measuring tube is fixed, respectively, in one of the end sections, wherein the measuring tube between the two fixing units can be excited to perform flexural vibrations of different modes with different natural frequencies, wherein of said modes a mode f1 does not have any vibration node between the fixing units, and wherein a mode f3 has two vibration nodes between the fixing units, wherein the procedure comprises the following steps: Determination of the natural frequency of mode f1 and of mode f3; Determination of a first provisional density value for the gas conducted through the measuring tube on the basis of the natural frequency of mode f1; Determination of a second provisional density value for the gas conducted through the measuring tube on the basis of the natural frequency of mode f3; Determination of a value for the sound velocity of the gas conducted through the measuring tube, and of at least a corrective term, which depends on the sound velocity and the natural frequency of a mode, for the provisional density value, which has been determined on the basis of the natural frequency of the mode, for the purpose of determining a corrected density measured value; wherein the corrective term K i for the provisional density values ρ i on the basis of the natural frequency of the mode f i has the following format: K i: = 1 + r g ⋅ c f i 2 − b, with ρ corr ⋅ = ρ i K i where rand g are constants that are independent of gas, c is the sound velocity of the gas, f i is the natural frequency of the mode f i, ρ corr is the corrected density and b is a scaling constant. Determination of the natural frequency of mode f1 and of mode f3; Determination of a first provisional density value for the gas conducted through the measuring tube on the basis of the natural frequency of mode f1; Determination of a second provisional density value for the gas conducted through the measuring tube on the basis of the natural frequency of mode f3; Determination of a value for the sound velocity of the gas conducted through the measuring tube, and of at least a corrective term, which depends on the sound velocity and the natural frequency of a mode, for the provisional density value, which has been determined on the basis of the natural frequency of the mode, for the purpose of determining a corrected density measured value; wherein the corrective term K i for the provisional density values ρ i on the basis of the natural frequency of the mode f i has the following format: K i: = 1 + r g ⋅ c f i 2 − b, with ρ corr ⋅ = ρ i K i where rand g are constants that are independent of gas, c is the sound velocity of the gas, f i is the natural frequency of the mode f i, ρ corr is the corrected density and b is a scaling constant.