Spontaneous nonlinear oscillations of surface tension produced by transfer of either octanoic or nonanoic acids from a droplet situated in the hulk water to the air/water interface are studied experimentally It is shown that the oscillation amplitude decreases significantly with the increase of pH of aqueous phase At pH > 6 5, detectable oscillations for the two fatty acids studied do not exist The results are discussed in terms of the mechanism proposed recently for spontaneous oscillations produced by transfer of nonionic surfactants