Several scholars and organizations suggest that institutional policy is a key enabling factor for academics to contribute their teaching materials as open educational resources (OER). But given the diversity of institutions comprising the higher education sector--and the administrative and financial challenges facing many institutions in the Global South--it is not always clear which type of policy would work best in a given context. Some policies might act simply as a "hygienic" factor (a necessary but not sufficient variable in promoting OER activity) while others might act as a "motivating" factor (incentivizing OER activity either among individual academics or the institution as a whole). In this paper, we argue that the key determination in whether a policy acts as a hygienic or motivating factor depends on the type of institutional culture into which it is embedded. This means that the success of a proposed OER-related policy intervention is mediated by an institution's existing policy "structure", its prevailing social "culture" and academics' own "agency (the three components of what we're calling "institutional culture"). Thus, understanding how structure, culture, and agency interact at an institution offers insights into how OER policy development could proceed there, if at all. Based on our research at three South African universities, each with their distinct institutional cultures, we explore which type of interventions might actually work best for motivating OER activity in these differing institutional contexts.