A system and a method for providing information on two of the three variables, density (.rho.), viscosity (.eta.), and elastic modulus (c) of a fluid, such that independent knowledge of one variable allows the remaining two variables to be measured by a single sensor. The present invention relies on the interaction of a predominantly shear horizontal acoustic wave device ("quasi-shear-horizontal") with the fluid, so as to measure subtle differences in the interaction of two or more acoustic resonance states or waveguide modes of a multi-mode resonator or waveguide, and to derive the desired fluid characteristics therefrom. The most preferred embodiment is a dual-mode coupled resonator filter geometry with one resonant mode having a high degree of symmetry and the other having a high degree of anti-symmetry. By combining the additional information of multi-moded operation with the inherent ability of a horizontally-polarized quasi-shear-horizontal acoustic wave device (AWD) to operate in fluid environments, one obtains a multi-mode quasi-shear-horizontal (MMQSH) resonator.