Several processes involve two immiscible liquid phases where the drops of the dispersed phase are surrounded by a continuous phase. The drops coalesce for joining their mother phase. This phenomenon occurs in many industrial mixing, separation, as well as in environmental processes. This paper is focused on the problem of the coalescence of a single drop at the interface with its mother phase. An original model characterizing the mechanism of coalescence is proposed and then validated by comparison with experimental data both from the literature and from the authors. (C) 2011 Elsevier Ltd. All rights reserved.