Higher education and associated institutions are beginning to share teaching materials known as Open Educational Resources (OER) or open courseware across the globe. Their success depends largely on the willingness of academics at these institutions to add their teaching resources. In a survey of the literature on OER there are several articles that discuss reasons why academics should contribute teaching materials. There are fewer articles that refer to academics' concerns or why they choose not to contribute their teaching resources. There have been only a few reported empirical studies thus far, and most of the studies have not been framed within any particular theoretical perspective. Hence there is a need to explore possible theories that might help to conceptualise and explain what enables or constrains the open education movement. This study aims to ascertain whether Engestrom's activity theory and its principle of contradictions is a sufficiently versatile and insightful lens to investigate non-participation of OER contribution. Activity theory was found to be useful for framing the literature and three interviews with University of Cape Town (UCT) academics and for surfacing some of the constraints in the system. The key concerns that emerged centred around the rules in the institution concerning promotion and what is valued by the institution. At present this institution places value on research and until value is placed on sharing teaching materials as OER, it is unlikely that there will be large-scale voluntary contribution to the UCT OpenContent directory. (Contains 1 table, 1 figure, and 2 notes.)