The ocean frontier has become central to a range of new and emerging strategies aimed at realizing the potential of the ocean economy. The purpose of this paper is to critically examine the configuration of the ocean as a frontier and its role in transforming marine spaces through the case of salmon aquaculture in Canada. To this end, we engage with ‘frontier assemblage’, an analytic that is developed from scholarship on agrarian and extractive resource frontiers in Asia. We use this approach to identify and extend three interrelated conceptual sensibilities. First, we use ‘frontierization’ to suggest that ocean frontier spaces are not only articulated at leading edges. Instead, frontierization happens at indeterminate sites, including those that have undergone earlier rounds of capitalist resource extraction. Second, we explore how ocean frontier resource extraction is assembled in ways that are indeterminate, but not radically open. Using the case of salmon aquaculture in Newfoundland, we show how resource extraction could have been ‘otherwise’. Third, we critically assess the promissory politics that are key to the ocean frontier. We argue that the frontier assemblage analytic—and the sensibilities we use—provides an approach to critically assess strategies aimed at realizing the ‘untapped’ resources of the ocean frontier.