Abstract: A surface acoustic wave (SAW) sensor system and associated method for accurately measuring mercury gas concentrations. The sensor includes a SAW device that may be a SAW delay-line oscillator or a SAW resonator. The surface of the piezoelectric substrate of the SAW device includes a material suitable for amalgamation with mercury. Mercury in the gaseous environment is captured with the amalgamating material so as to cause a change in the mechanical and electrical properties on the surface of the device, thereby causing a change in the frequency output of the device. The piezoelectric substrate of the SAW device is preferably coupled to a heater to permit control of the temperature at the surface of the device. The piezoelectric substrate temperature may be regulated to produce a substantial equilibrium of mercury amalgamation/desorption kinetics. Under the conditions provided by the invention, the mercury concentration in the gaseous environment can be determined.