Ingroup bias found in the Minimal Group Paradigm is an important finding for theories of intergroup relations. However, explanation of the finding is controversial. In this study, we contrast the Social Identity Theory explanation of ingroup bias with a new alternative hypothesis. We argue that ingroup bias is a result of subjects employing a self-interested quasi-strategy in an attempt to gain greater material benefits for themselves. Although the strategy cannot be successful, we argue that the interdependence situation characteristic of the Minimal Group Paradigm deceives subjects into believing it can be successful. Consequently, when subjects are not dependent on other subjects for their own rewards in the Minimal Group Paradigm, ingroup bias disappears. Results of our experiment support the interdependence hypothesis.