This article analyzes whether and to what extent energy resources fulfil the definition of military objective within the meaning of international humanitarian law (IHL) and customary IHL. In order to bring conceptual clarity to the duty to protect the natural environment in armed conflict, the article explores the legal limits to the destruction of energy resources (that are part of the natural environment) controlled by armed non-State actors during non-international armed conflicts (NIACs). It examines the practice of the United States, which characterizes the destruction of the natural environment during hostilities as being related to targets that contribute to the “war-sustaining capability” of enemies. Conceptual light is shed on the legality of attacks on oil refineries and installations during NIACs as a matter for IHL.