Petroleum exploration in eastern Panama and northwestern Colombia has gained impetus by recent side-looking-radar, geologic reconnaissance mapping. Radar-derived geologic information is now available for approximately 40,000 sq km where previous reconnaissance investigations have been extremely limited because of inaccessibility and almost perpetual cloud cover.

With radar imagery as the sole source of remote-sensing data, the distribution, continuity, and structural grain of key strata provide evidence that the eastern Panamanian Isthmus can be divided into three main physiographic-structural parts: two composite coastal mountain ranges separated by the taphrogenic Medial basin, which trends southeastward from the mouth of the Bayano River to the Atrato River valley of northwestern Colombia. Within the Medial basin, most of the clearly exposed surface structures are not particularly attractive petroleum prospects because prime reservoir strata have been stripped from their crests. However, several large geomorphic anomalies which have been mapped in the Medial basin may be reflections of subsurface structures having a complete stratigraphic ection. Possibilities for gravity-type hydrocarbon accumulations in fractured organic shales, siltstones, and carbonate rocks are suggested within several synclinal elements along the axis of the Medial basin. The southwestward extension of the Medial basin trend, coincident with the western Gulf of Panama, may have potential as a future petroleum-producing province. A relatively thick marine stratigraphic section should be present here, with associated paralic and deltaic clastic rocks derived from acidic San Blas terrace since mid-Miocene time. The occurrence of active shell bars in the Bay of San Miguel and present reef trends on the northern Caribbean coast suggest possible offshore sites for geophysical surveying.