Three experiments examined the impact of groups on the formulation of ultimatum offers, that is, whether the offer was formulated by an individual or by a group, whether the offer was formulated for an ingroup or an outgroup, and perspective, which refers to the formulator's beliefs about the criterion the other would use in deciding to accept or reject the offer. We experimentally tested two perspectives: "rational," where the other was expected to accept any amount offered because it would be better than nothing, and "fair," where the other was expected to use fairness as the criterion for evaluating the offer. The latter perspective implies a need to show greater cooperation, i.e., to make more generous ultimatum offers. The results supported the hypotheses that groups adopt more of a rational perspective than individuals, and that offers to outgroups reflect a rational perspective more than offers to ingroups. The preference of the most competitive individual in the group was the best predictor of the group's ultimatum offer. The perspective adopted by the group had lasting effects, as individuals tended to adopt the level of competitiveness of their groups in subsequent individual ultimatum games. (C) 1997 Academic Press.