In recent years, scholarshave turned to alternative representationsof utility to capture motivationalheterogeneity across individuals. In theresearch reported here, we examine twomodels of heterogeneous utility –linear-altruism and inequity-aversion – inthe context of two-person, social dilemmagames. Empirical tests are conducteddrawing on data from experiments andsurveys. We find that the model ofinequity-aversion accounts for asubstantial proportion of the preferencetypes and behavior that are not explainedby the standard model of self-interestedpreferences. In contrast, the altruismmodel does not provide a significantincrease in explanatory power over theinequity-aversion model.