It is known that evaluating oscillatory rheological shear experiments in the usual way may lead to complete misinterpretation of the experimental data, especially for low viscosity fluids in the high frequency range. We used a modern type of oscillatory rheometer with a stiff transducer. When measuring Newtonian liquids artificial, second‐order fluid‐like data for the complex shear modulus were found. In order to explain those findings, it is essential to take into account the influence of fluid inertia. Accordingly a method, based on theoretical considerations, is suggested for the correction of experimental data for slightly elastic fluids in order to obtain the true viscoelastic material functions.