We describe a vibratory vacuum gauge in which a small force due to high-frequency compression of a gas excites a planar mechanical oscillator. Compared to vibratory viscosity gauges, this principle allows operation at lower pressures. With a prototype apparatus we demonstrate sensitivity from 10(5) to 10(-4) Pa for argon, nitrogen, and helium. A simple theory for the device is presented which gives an account of the pressure and molecular weight dependence of the response in the molecular flow regime. (c) 2006 American Vacuum Society.