Binary coalescence phenomena of two oil drops formed at the tips of single nozzles were observed. Through the observations, the time requirement for the coalescence of drops was found to be dependent on the nozzle diameter. The effect of nozzle size was evaluated by consideration of the force acting on the drop, and then the real coalescence time, which is independent of nozzle size, was determined. The coalescence time was shown to increase with increasing drop-size and with decreasing size-difference between drops. This tendency was expressed in a simple functional form. In addition, the effect of physical properties of drops was briefly discussed.