Recent scholarship has highlighted ‘assetization’ as an increasingly prevalent process in which valuation practices from financial economics are imposed on new aspects of society. This paper analyses the establishment of the Norwegian ‘oil fund’ – currently the world’s largest sovereign wealth fund – as the outcome of such a process. It traces the shift in the Norwegian government’s valuation arrangements from valuing oil as ‘activity’ in the 1970s towards valuing oil as a ‘national asset’ from the mid-1980s, and shows how this shift happened through close exchanges between economic expertise and governmental procedures. The paper contributes to understanding assetization as a mode of governing by showing both how it happens through governmental tools and practices and how it can have direct material consequences. In the case of Norwegian oil, the introduction of new tools of valuation made the Norwegian government manage the oil resource in a new way, and led to a re-timing of the pace of its extraction. The outcome was speeding up the conversion of oil into financial holdings, and the establishment of the ‘oil fund’ as a new infrastructure for handling oil as a national asset.