The development of a prototype liquid level sensor using a thin walled cylinder vibrating in a circumferential mode and thin film piezo-electric polymer transducers is presented. Vibration characteristics of the fluid loaded cylinder are analysed with a finite element model incorporating the'added mass' concept. The model is shown to predict the prototype sensor performance. It is also demonstrated that a series of non-dimensional graphs of the modal characteristics of empty cylinders can be used to predict the performance of this family of level sensors and provide a valuable design tool in the selection of suitable cylinder dimensions.