China caught the oil industry by surprise during the Iran war, pulling powerful levers to shield itself from the biggest energy shock in decades. In the process, it established itself as a new force in global energy markets - an independent, opaque, massive power. The measures China used to offset the energy supply shock - sharply cutting crude imports, restricting exports of refined fuels and drawing on domestic inventories - culminated in a decades-long campaign to reduce its heavy dependence on overseas energy supplies. This offers a glimpse into how future crises could play out.