To achieve the dual goals of minimising global pollution and meeting diverse demands for environmental justice, energy transitions need to involve not only a shift to renewable energy sources but also the safe decommissioning of older energy infrastructures and management of their toxic legacies. While the global scale of the decommissioning challenge is yet to be accurately quantified, the climate impacts are significant: each year, more than an estimated 29 million abandoned oil and gas wells around the world emit 2.5 million tons of methane, a potent greenhouse gas. In the US alone, at least 14 million people live within a mile of an abandoned oil or gas well, creating pollution that is concentrated among low-income areas and communities of colour. The costs involved in decommissioning projects are significant, raising urgent questions about responsibility and whether companies who have profited from the sale of extracted resources will be held liable for clean-up, remediation and management costs. Recognising these political goals and policy challenges, this article invites further research, scrutiny and debate on what would constitute the successful and safe decommissioning of sites affected by fossil fuel operations – with a particular focus on accountability, environmental inequality, the temporality of energy transitions, and strategies for phasing out or phasing down fossil fuel extraction.