The factors affecting the adoption of open educational resources (OER) in higher education have become a research topic of great interest as OER continue to be widely used in universities, affecting the quality of teaching and learning. The reasons for OER adoption are diverse, across both individual educators and cultural environments. This study explored determinants of OER adoption by university educators in three cultural contexts utilizing the Unified Theory of Acceptance and Use of Technology (UTAUT2). Data on educators' behavioral intention to adopt OER were collected from 152 educators in three countries, Korea, Japan and the United States. In every culture, habit was the strongest determinant of this behavioral intention. Other highly significant factors affecting OER adoption by educators varied by culture. In Korea, the strongest determinant was performance expectancy, in Japan it was social influence and in the United States it was price value. The moderating effect of culture was significant on three paths of the model, and the cultural specificity affecting OER adoption was substantial. Theoretical and practical implications related to the UTAUT2 model and OER policy are discussed.