Ghost interference on small airgun signatures h been experimentally investi gated. A vertical hydrophone array w designed to receive the a gun energy output at di erent hydrophone depths. The airgun signatures were Fourier transformed to analyze the dominant equency energy distribution. It was found that dominant equency energy variation versus airgun depth could be described by a parabolic function. This result provides a good explanation r some con icting points pr posed by previous investigators. The determination of an optimum a gun depth by this method is particularly valuable seismic records are to be processed without deghosting. A simple ghost interference model is proposed to explain the a gun depth of greater energy output and the depth of the less bubble pulse e ect. The optimum airgun depth should compromise between the ghost interference and the desired equency band in the seismic survey.