Since 1940 Mexico has increased exploration work in search of new oil fields. Most of the exploration has been done in the Gulf Coast area where all existing Mexican oil fields are located. A brief resume is given of the main problems of the different provinces under exploration and a list of the fields discovered by Petroleos Mexicanos in the different provinces of the country. Geophysical methods have been responsible for location of a very large percent of the new fields. To compare the intensity of exploration in the United States and Mexico, the amount of seismic and gravity-meter work and of wildcat drilling per million barrels of production is given for both countries. The data shows that Mexico's level of geophysical exploration, per million barrels of oil produced, is very close to that of the United States. A very marked increase in the intensity of exploration is shown for both countries. Wildcat drilling in Mexico has been less intensive than in the United States but shows a definite tendency to increase; its present level is very close to that of the United States during 1940. The writer is of the opinion that the difference in intensity of wildcat drilling shown in the data presented is actually smaller than appears as there is a certain amount of duplication in the United States because of lease holding problems.