This research analyses the barriers and enablers of OER adoption at three South African universities, in order to better understand why South African lecturers adopt – or do not adopt – OER. Based on interviews with 18 lecturers at the universities of Cape Town (UCT), Fort Hare (UFH) and South Africa (UNISA), this qualitative study focuses on lecturers’ teaching practices as they relate to (potential) open educational activity. To do this, the study developed and utilised three key analytical frameworks and concepts for assessing and comparing OER (in)activity at the universities. First, because the factors shaping lecturers’ adoption of OER are both immediate (over which they have personal control) and remote (over which they have less or no control), we developed an “OER Adoption Pyramid” to help analyse, compare and explain the factors that act as barriers or enablers. The pyramid is comprised of six layered factors which, together, determine whether OER adoption can take place at an institution: infrastructural access, legal permission, conceptual awareness, technical capacity, material availability and individual or institutional volition. Second, based on the insights generated by the pyramid, the study also developed “OER Readiness Tables” to provide a visual representation of the institutions’ obstacles and opportunities – their level of “readiness” – for OER engagement. Third, the literature on “institutional culture” helped nuance these comparisons so that the analysis could remain attentive to more granular, idiosyncratic and local variables shaping OER decision-making. The diversity of the institutions – UCT (urban, contact, collegial), UFH (rural, contact, bureaucratic) and UNISA (distance, correspondence, managerial) – necessitated an appreciation of how the factors were shaped by their institutional cultures. We believe this research – and these analytical frameworks – will have value for OER scholars interested in researching OER adoption, and institutions interested in promoting it.