The first half of the 20th century centered on the struggle between countries where the oil was found, the countries where oil was consumed, and those few powerful companies with the technology and knowhow to make that oil economically viable. But once oil-producing countries learned the basic ins-and-outs of the oil business, these oil-producing countries in all but a few cases seized control of their reserves and production, starting in the late 1930s but most radically and comprehensively in the 1970s. For the last fifty years then, a central puzzle of the global oil industry relates to the striking diversity of NOCs; in other words, what makes national oil companies so different between themselves?—whether, as ‘companies’, in their ability to perform the ‘core’ duties of the oil business, or as ‘national’ entities, in the tasks they perform for their home-states.