Disclosed is a method for determining the contents of a gas bottle, in particular a liquid gas bottle, comprising the following steps: First of all, the gas bottle is excited by applying a signal to a loudspeaker mounted on said gas bottle. The signal from a microphone mounted on the gas bottle is compared in phase with the signal used for excitation, with the frequency of the signal applied to said loudspeaker being altered continuously, until a resonant frequency is established. This resonant frequency is converted into a filling level of the gas bottle according to a previously determined relationship between the resonant frequency and the filling level. Furthermore, an apparatus is disclosed with which the above-mentioned method may be put into practice.