State-controlled oil companies—so-called national oil companies (NOCs)— remain firmly in control over the vast majority of the world's hydrocarbon resources. These enterprises differ markedly in the ways they are governed and the tightness of their relationship with government. NOCs also vary in their geological gifts, as some are endowed with prodigious quantities of "easy" oil while others must work harder and apply highly advanced technologies. The case studies in this document explore whether and how these and other factors actually explain the wide variation in the performance of NOCs.