As offshore assets age, oil and gas companies face a wave of decommissioning obligations, with expenditures estimated to exceed US$200 billion in coming decades. Decommissioning is not simply demolition. It requires plugging and abandonment of subsea wells. It requires reverse engineering structures in order to dismantle them safely and efficiently. It requires the destruction or recycling of substantial waste products, including hazardous chemicals. It also may require substantial environmental remediation. Decommissioning represents not just an operational challenge but also a legal one. The global dispersion of facilities and their offshore location necessarily implicates a complex and overlapping set of international, regional, national, and intranational legal regimes. Decommissioning activities inevitably will entangle oil and gas companies in a wide range of disputes, including with host governments, regulators, business partners, and contractors.