The theory of regionalized variables has been used in Chile and Argentina on the Atlantic side of the Andes in the study of reservoir locations in the onshore part of the Magellan basin to gain information that may be useful in exploration elsewhere in the basin. Practical utility of the method of regionalized variables is shown in a study of the Cullen field of the Magellan basin. Within this complex productive area it is possible to differentiate between areas having high or low probabilities of success for the discovery of oil. Techniques used include universal kriging, an estimation procedure for grid generation in automatic contouring, and drift analysis. The drift is an estimate of a slowly varying spatial component such as that usually studied by trend-surface anal sis. Provided the assumptions of the theory are met, estimates of the form of the mapped surface are unbiased with minimum estimation variance. Most importantly, the methods yield an estimate of the possible error at every point on a map.