Northern coastal Peru, including the area of International Petroleum's La Brea-Pariñas field, is a region of marked subsurface structural relief. This relief consists of a complex series of basement highs and which, in general, have retained their respective high or low tendencies at least as far back as the early Tertiary, and therefore have influenced in varying degrees, the nature and distribution of faunal and sedimentary facies deposited here since that time. Production is almost entirely from Eocene sands which occur both in lenticular and blanket-type deposits. However, because of intercalated shales, different degrees of cementation, and faulting contemporaneous, or nearly so, with deposition, the oil has had virtually no opportunity to migrate. Accordingly, this region is an excellent place in which to study the relationships among the occurrence of oil, the structure, and the sedimentary facies. From such study, the following observations have been drawn—1. The oil is of local origin, greatest migration being probably less than a mile. 2. Sedimentary facies are of prime importance in the control of oil occurrence. 3. Structure is important chiefly in the way it has controlled the deposition of source beds in relation to reservoir beds, rather than in simply providing closure by which to trap migrating oil. 4. For best results, the oil should be sought in areas where reservoir and source beds have been developed on the basis (sand-shale ratio) of about one to two, or one to three. These areas occur more commonly on the flanks of active structures rather than on top of them, or deep in the basins.