The Mexican oil expropriation was one of the most dramatic in Latin American history and it had major implications both for the international oil industry and for the Mexican Revolution. The Cárdenas presidency (1934–40) did much to institutionalise the Mexican Revolution as Lázaro Cárdenas looked for support beyond the small secular elite which had triumphed under Carranza. He organised the Mexican working class and peasantry and incorporated his supporters into the Revolutionary Party. The oil nationalisation of 18 March 1938 was one of the high points of his programme and Mexican politics subsequently evolved in a far more conservative direction. The nationalisation marked a dramatic assertion of economic independence from the major oil companies and their parent governments and it was certainly widely supported within Mexico. Beyond this, however, lie some very difficult problems of interpretation and many of Cárdenas's own motivations remain shrouded in mystery, as do his relationships with key political insiders. The British diplomat who complained at the beginning of 1938 that ‘a kind of oriental fog of secrecy and intrigue and misrepresentation covers the struggle going on all the time between the President, his advisers, the syndicates, the Generals and so on’ was probably no less well informed than many later historians.

It is certainly clear, however, that the initial impetus towards oil nationalisation came not from diffuse popular pressure but from the political elite.

When the Ecuadorian military took power in February 1972, it found an oil industry which was economically quite well developed but which remained a mystery to almost all Ecuadorians. Ecuador had produced some oil ever since 1918 but the amounts had been small and successive regimes had hardly concerned themselves with oil policy. For many years, Ecuador levied few taxes, had no state company and knew extremely little about the industry. In some ways, therefore, the events of the years 1972–6 may be regarded as providing something of a learning process for Ecuador, after which policy became less dramatic and rather more settled. The 1972–6 period was extremely eventful, both nationally and internationally, and a great deal was telescoped into a very short period of time. Ecuador began large-scale exports of oil in June 1972 and by 1974 the Ecuadorian Oil Minister had become President of OPEC. Only in 1977 did some kind of conservative ‘normality’ return, and this was followed in 1979 by the election of a reformist civilian government.

Expansion and renegotiation 1969–73

The Ecuadorian oil boom got seriously underway in 1967 when a major discovery was made in the Oriente. Until that time Ecuador's smallscale oil production had come entirely from the coastal area; it was widely believed that there was oil to be found in the Oriente but until then no commercially attractive discovery had been made.

There are, broadly speaking, two ways in which the international oil system can be analysed. One of these is essentially derived from liberal economic theories and stresses the importance of factor endowments and comparative costs in explaining international trade. The other is basically Marxist (although shared by some conservatives) and argues that trade, even where it does not follow the flag, is nevertheless mainly determined by international power relationships. Now that evidence has been presented, it may be interesting to consider how these different approaches can be applied to the oil system in the twentieth century.

To begin with the first approach, it is certainly true that the history of international oil has been made up in large part by such environmental factors as the international distribution of population and potentially oil-bearing territory. Moreover, policy can very often be understood in terms of these factors. Let us therefore consider the geological conditions that have existed in Latin America during the course of the century and their effect upon policy.

Two Latin American countries, Venezuela and Mexico, have been actually or potentially oil rich during most of the century in the sense that there was not only enough oil to be found and exported on a large scale but also adequate technology for the purpose as well as geological conditions which made these sources relatively low cost.

The middle 1950s was a high-water mark for the major companies. The Iranian challenge had been defeated and producer governments were quiescent. Rapidly increasing demand in Europe allowed the progressive development of the highly profitable Middle Eastern finds without creating major tensions elsewhere. The major oil-exporting countries were still being developed almost exclusively by consortia in which the major companies had controlling interests, and elaborate schemes had been arranged to regulate the supply of oil from these countries. In the following 15 years, however, this position was steadily eroded; the actions of producer governments, although essentially defensive, became increasingly important after the formation of OPEC in 1960, but the immediate challenge to the majors came from the independent companies – the newcomers – who were becoming increasingly prominent in the search for foreign oil supplies. Under these circumstances, world prices began to erode and this erosion brought further tensions and conflicts into the international oil market.

The first significant erosion of the major companies' control over the most important non-us oil reserves came in Venezuela, where in 1956 Pérez Jiménez offered a massive new round of concessions to the highest bidders. Good oil prospects, proximity to the USA and a government eager to supplement its major source of income all attracted independent us companies which were willing to undercut established suppliers in order to find marketing outlets.