The dependence of an acoustically resonant optoacoustic signal on the molecular weight and thermodynamic and transport properpties of the buffer gas is reported. Our results show that careful selection of such gases can significantly increase the sensitivity and flexibility of optoacoustic spectroscopy. We also demonstrate that such thermodynamic quantities as &ggr; (≡Cp/Cv) and sound velocity can now be measured readily and accurately. Other potential applications are suggested.