Interfacial or surface tension exists when two phases are present. These phases can be gas/oil, oil/water, or gas/water. Interfacial tension is the force that holds the surface of a particular phase together and is normally measured in dynes/cm.
Pendant drop method: The shape of a drop on a needle in a bulk liquid phase is determined, among other things, by the interfacial tension. The interfacial tension can be ascertained from the image of the drop using drop shape analysis.