The Lusitanian basin covers coastal Portugal and the adjacent offshore and received sediments from Triassic to Tertiary time. Presence of source beds, reservoirs, diapirs, and surface indications has attracted exploration since the late 1940s. Three principal potential source-rock zones have been identified from surface and subsurface work: Permian coals and Lower and Upper Jurassic kerogenous beds. The Permian coals occur only in localized basins and are of limited significance only as a potential gas source. The Lower and Upper Jurassic potential oil source rocks are confined to two subbasins in the center of the Lusitanian basin. Net source-rock thickness decreases from the subbasin centers toward the rims. Source maturity, established by various and independent techni ues, appears to be rather low, suggesting a low resulting generation, expulsion, and migration efficiency. Surface indications and crude oil derived from tests support the hypothesis of a not very mature system. Although the subsurface data confirm the early interpretation that the Lusitanian basin contains the necessary basic ingredients for a successful exploration play (i.e., structures, reservoirs, source rocks), the absence of sufficient source maturation

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seems to be a downgrading factor, at least for parts of the basin explored.

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