The geometric-mean drive-point admittance (or “mobility”) of a complex structure is given by the admittance of the corresponding infinite structure (i.e., the “characteristic admittance,”Yc). The frequency response of an infinite plate, for example, coincides with the geometric-mean response of a finite one. Eugen Skudrzyk’s “mean-value theorem” was derived and experimentally verified without consideration of fluid loading. This paper shows that Skudrzyk’s method can be applied to fluid-loaded plates well below the coincidence frequency. Skudrzyk’s general mathematical expression allows simplified modifications that account for fluid loading and result in an approximate fluid-loaded characteristic admittance that differs only by a small multiplicative factor(<2 dB)from a correct analytical expression derived by Crighton.