Abstract 2D finite element simulations are performed on QCM working in the thickness-shear mode and loaded with different&#xD;homogeneous films. They include a purely elastic film, a viscoelastic Maxwellian liquid, viscoelastic-Voigt solid, and&#xD;the fractional (power-law) version of each case. The films are tested in air or covered with liquids of different viscosities.&#xD;Two substrate thicknesses are tested: 100nm and 500nm, the latter being close to the condition that promotes the&#xD;resonance of the adsorbed film. In all cases the simulations are compared with small-load approximation theory.&#xD;The 100nm films follow the theory closely, although significant deviations of the SLA are observed as the overtone&#xD;order increases even in purely elastic films. We also show that it is possible to identify the viscoelastic “fingerprint” of&#xD;the 100nm films in air using raw data and Sauerbrey’s equivalent thickness obtained with the QCM in the 3 < n < 13&#xD;range. These numerical data are validated by experimental measurements of crosslinked polydimethylsiloxane films. In contrast, the 500nm films deviate notoriously from the SLA, for all viscoelastic models&#xD;and overtones, with the largest deviation observed in the elastic film. When a liquid layer covers the QCM without an&#xD;adsorbed film, the only overtone that numerically reproduces the theoretical value is the fundamental, n = 1. For n > 1,&#xD;strong coupling between the solid and liquid is detected, and the original vibration modes of the crystal are altered by&#xD;the presence of the liquid. Finally, the numerical simulations suggest that it is possible to detect whether a viscoelastic&#xD;film is formed under a liquid layer using only the information from n = 1. In these film/liquid systems we also observe&#xD;the so-called missing-mass effect, although the theory and simulations exhibit different levels of impact of such effect&#xD;when the liquid viscosity is high.