The motion of single liquid drops in a swarm of other drops in a rotating disk contactor has been observed by employing a (viscous) matched refractive index system (octanol/aqueous sucrose solution). The breakage probabilities of drops in a swarm have been observed and compared with those of single drops. Single drop velocity is different above and below rotors. The ratio of characteristic velocity (over the whole compartment) and terminal velocity at first decreases with increasing continuous-phase viscosity and then increases above 1.0, probably due to shape and drop orientation changes under the influence of agitation. Single drops in a swarm obey slip velocity relationships similar in form to that for the swarm, but the relationship between them is not yet clear. Single drop breakage probability in a swarm decreases as dispersed-phase flow rate increases and continuous phase flow rate decreases if rotor speed exceeds the critical value for breakage, but the behavior is more complex if this is not the case.