We consider an assembly of liquid drops imbedded in another immiscible liquid of similar viscosity. It is shown that a coalescence between two drops induces another coalescence when the average distance between the drops is less than a threshold value, resulting in a “chain reaction” of coalescences. The threshold value is calculated using a “shell” model that is based on the boundary integral approach. Another “many-drop” model is developed to test the shell approximation. We show that, although the shell model is adequate, its results can be improved by lowering the shell surface tension.