The extent to which group members contribute effort efficiently, i.e. to the extent that their efforts add to the group product, or equally to their fellow worker is investigated as a function of group members' expectations about future interdependence. An experimental set-up was employed in which (1) participants were able to determine what would be an efficient and what would be an equal amount of effort to exert, and (2) in which efficiency and equality required different levels of effort: Participants worked on a physical motor-production task and expected to work with a partner twice (continued interdependence) or only on the first task (no continued interdependence). Before working on the first task, they received information about their relative task ability (high versus low) and information about their partner's effort expenditure (high versus low). It is argued and demonstrated that group members expecting continued interdependence are likely to equal their fellow worker's effort expenditure, whereas group members expecting no continued interdependence are likely to exert effort efficiently. The results are discussed from various theoretical perspectives. Copyright © 2001 John Wiley & Sons, Ltd.