Abstract: The application of nonlinear backscattering of acoustical signals in detection of gas bubbles in subsurface layer of sediment of the Gulf of Gdansk is presented. Gas bubbles concentration was estimated assuming that nonlinear scattering in soft sediments is similar as in water. Summary, difference and double harmonics generated only by gas bubbles were recorded and used for bubble density estimation. Comparisons of the concentrations received from different nonlinear components show generally agreement in calculated bubble density distributions, although values of densities acquired from almost identical volumes in a single transmission differ.