It is generally agreed that lateral vibration of reactor fuel elements is random in nature and is caused by random pressure fluctuations acting on the element surface. A series of tests has been conducted in which a single test element has been subjected to two-phase parallel flow in a circular annulus. Statistical properties of the amplitude of vibration have been measured for various simulated steam qualities with fixed mass flow rate. Statistical properties of the two-dimensional pressure field surrounding the element have also been taken. These properties have been used in conjunction with the linear random vibration theory to arrive at predicted values for vibration amplitude. Good agreement has been found between measured and predicted values of vibration amplitude. It is shown that a high peripheral correlation of the driving forces is primarily responsible for the larger vibrations encountered in two-phase flow. Spectral analysis of the driving forces has been provided with a view toward providing useful information for fuel design.