The PreRif Basin in northern onshore Morocco may contain major oil and gas reserves. This foreland basin is located between the Tertiary-Recent Rif Orogen to the north and the stable Moroccan Meseta to the south; for the purposes of this paper it includes the Rharb Basin, an area of strong Neogene subsidence which extends offshore to the west. Prospective sandstone and carbonate reservoirs are present at a number of stratigraphic levels, ranging in age from Triassic and Jurassic to Miocene and Pliocene. Lower and Middle Jurassic shales and carbonates constitute potential source beds for ＇＇thermal＇＇ oil and gas; biogenic gas is generated within Miocene/Pliocene shales. Potential source beds are expected to have reached thermal maturity in the deepest portions of the present basinal area since the Late Miocene. Seals are provided by intraformational shales, transgressive shales of Tertiary age, Triassic evaporites, and by a thick, complex glidemass (or ＇＇olistostrome＇＇) of late Miocene (Tortonian) age. Multiple traps can be expected; they will include anticlines, fault closures, salt-tectonic features, and structural-stratigraphic traps. Gravity-defined low areas in the northern portion of the basin are probably the main generative depocentres. Lateral oil and gas migration has occurred on a regional scale since the Late Miocene, and has continued to the present day. A Jurassic Petroleum System includes the surface oil seeps and shot-in oilfields of the Sidi Cacem area along the basin＇s southern flank, A Miocene Petroleum System supplies gas production in the Rharb Basin. The prospective area covers some 15,000 sq. km. Available reconnaissance data include published gravity, magnetic, seismic, and surface-geological surveys. Modem airborne surveys of prospective areas should be followed by detailed exploration, including 3-D seismic surveys. New recover-able field reserves may lie in the range of 50 to 150 million barrels oil-equivalent per discovery; several new discoveries can be expected leading to new total reserves possibly totalling 0.5 billion barrels oil-equivalent.