The interfacial tension working at an interface created by sudden contact of liquid water with saturated common vapors of n-pentane and water under atmospheric pressure (0.101 MPa) was experimentally studied, focusing on the behavior of its relaxation to an equilibrium value in response to the progress of the adsorption of n-pentane molecules onto the interface. The oscillating-jet method was used to measure the dynamic interfacial tension, i.e., the interfacial tension varying with time during a short relaxation period (less than 0.1 s) after the creation of the interface. It was observed that during the first similar to 50 ms after the creation of the interface, the tension quasi-exponentially decreased from the normal surface-tension value for pure water (70.5 mN/m) to the equilibrium value (61.5 mNm) which had been obtained in a previous study using the pendant-drop method. An attempt was made to correlate the obtained "interfacial tension versus time" data based on an adsorption/desorption kinetics model. (C) 2016 Elsevier Ltd. All rights reserved.