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The Marmul field lies in the Dhofar province of the Sultanate of Oman. The heavy oil accumulation was discovered in 1956 by Dhofar Cities Services who drilled five wells, but it was not considered commercial and operations were abandoned. Petroleum Development Oman acquired the concession in 1969. Producible oil occurs in Paleozoic clastic rocks overlain unconformably by a Cretaceous sealing shale. Initial appraisal showed the complex nature of the reservoir distribution to be due to its glacial to periglacial environment of deposition and a simple geologic model was conceived. Seismic impedance contrast at the seal's unconformity surface was then used as a predictive tool to differentiate glacial waste zones (tillites) from periglacial reservoirs and as a support for the continuing appraisal and development drilling. The glacial to periglacial geologic model was progressively refined by further development drilling. The appraisal effort based on geologic and seismic impedance models was then pursued toward possible additional younger stacked reservoirs stratigraphically trapped at the periphery of the field. Drilling proved these reservoirs to be separate from the main field and oil bearing. The unraveling of the field's complex trapping mechanisms and the refinement of the geologic models needed for primary development and secondary recovery schemes could only be achieved through an integrated approach by geologists and geophysicists.