OPEC is an international organization of countries which export large quantities of oil. OPEC acts as a cartel, coordinating its members’ decisions on oil production and pricing. This is not illegal because, as countries, its members benefit from the international law doctrine of state immunity. OPEC’s decisions used to be the single most important factor in international oil markets. However, its influence declined, partly because US oil and gas production more than doubled between 2008 and 2019 to exceed those of OPEC leader and largest producer, Saudi Arabia.