We report a study of collaborative problem solving among 'groups’ of two and three people, collaborating face-to-face or supported by high quality videoconference links. Tasks were completed equally well in each condition but more talk was needed to accomplish the task when 3 individuals collaborated either face-to-face or in video-mediated conditions. Careful analysis of the problem solving dialogues, in terms of how 'common ground' was achieved, revealed the kinds of communicative functions that led to longer multiparty interactions. Lengthier stretches of talk occur characteristically where knowledge is distributed between two of the three individuals. Establishing common ground among three partially knowledgeable participants is particularly challenging in multiparty interaction. A high quality, multimedia communication system seems to be able to support this communicative process quite effectively.