The surface tension of the Cu-Sn system has been measured over the whole composition range by using the large drop method over the temperature range T = (430 to 1300) K. The measurements were carried out at equilibrium and under "oxygen-free" conditions. The results obtained were compared with the available literature data as well as with theoretical values calculated by the compound formation model (CFM) and quasi chemical approximation for regular solution (QCA). In addition, dynamic surface tension measurements have been performed to study the evolution of the molten alloy surface in the presence of trace amounts of oxygen in the surrounding atmosphere. The general physico-mathematical formalism developed by our group to study liquid binary alloys and their oxides has been applied to describe the interactions in Cu-Sn melts under an oxidizing atmosphere. The experimental findings validate the model predicting the oxidation phenomena which contribute to maintain the interface cleanness and to determine the boundary separating oxidation and deoxidation regimes.