<p>Understanding the limits of existing fossil fuel phaseout policies is key for clarifying the challenges of phasing out fossil fuels. In this article, I focus on Denmark as a prominent example of the tension between ‘fossil fuel leadership’ and ‘fossil-fuelled leadership’ due to the conflict between its self-positioning as a first-moving global climate leader and continued and new oil and gas production despite its phaseout policy. I examine the origins, appeal, and limits of Denmark’s climate and fossil fuel leadership claims and ambitions, using novel data from 27 interviews with key Danish climate and energy stakeholders. I argue that Denmark’s leadership ambitions contain major limitations, because despite its attempt to provide first-mover leadership, Denmark’s fossil fuel policy is insufficient. If even one of the most ambitious supply-side leaders falls short of its responsibility, this shows the need for more credible and extensive fossil fuel phaseouts in the global climate governance architecture to become a serious force for limiting the climate crisis. As climate leadership must be credible to be effective, the Danish case offers important cautionary lessons for policy-makers from other fossil fuel producing countries as well as climate and energy scholars.</p>