While the vast majority of oil pipeline projects in Canada have been successfully built, several mega oil sands projects within and passing through Canada have been cancelled or significantly delayed. This article explains why these delays and cancellations have occurred. A systematic cross-case analysis is used to provide insight into the changing politics of oil sands pipelines. Qualitative comparative analysis (QCA) is used to identify combinations of causal conditions that co-occur across

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... ses of proposed new oil pipelines and pipeline expansion projects. The pipeline projects were proposed to the federal regulator—the National Energy Board—between 2006 and 2014. The QCA reveals that social mobilization and major regulatory barrier(s) are necessary conditions in explaining variation in pipeline project outcomes. The analysis of sufficiency reveals more complex configurations of conditions. This article contributes to the literature on the politics of oil sands pipelines by using a comparative approach to identify the impacts of socio-political and legal dynamics that have emerged around pipelines in the last 15 years.