Despite the political controversies surrounding it, in Mexico as in other countries, oil exploration and production between 1900 and 1920 was primarily an economic activity developed by scientists, technologists, skilled workers and entrepreneurs. The Mexican oil fields were both drilling sites and ‘smithies of ideas’ where new cadres of oil professionals were producing fresh knowledge on the oil-bearing formations. Along with Mexican and British professionals, young US geologists with more books in their hands than oil on their shoes emerged and managed, in spite of having little experience, to push Mexico in less than one decade to the top-three list of petroleum-exporting countries. This article aims to present the business and scientific activities of one of the most relevant individuals among them, Everette Lee DeGolyer, assessing his contribution to petroleum exploitation and oil geology in Mexico.