Three large basement outcrop areas, designated here as provinces, define the Precambriann basement of Libya. These are: Al'Oweinat Basement Province (OBP) in southeast Libya extending into Egypt and Sudan, Tibesti Basement Province (TBP), which occupies a far central-south location with continuation into Chad, and Ghat Basement Province (GBP) in southwest Libya extending a little into Algeria. These litho-tectonic provinces show distinctive rock assemblages and deformational histories. Whereas Al’Oweinat basement is the oldest and encompasses Archean rocks, the latter two basement provinces consist of rock assemblages that are much younger and are considered to be of mostly Pan African age. All basement provinces encompass both metamorphic and igneous rock suites in different proportions. Metamorphism is prevalently regional, but there is evidence of limited contact and retrograde metamorphism in places. Throughout all three provinces the metamorphic terrain is pierced by (syn-tectobic to post-tectonic) igneous bodies of different forms and sizes displaying granitic to gabbroic mineralogy. Although not a basement component, Tertiary ring intrusions of oversaturated to undersaturated composition add to the diversity of the igneous rocks of Al'Oweinat region.

Scattered basement rocks also occur in the areas of the Gargaf Uplift and Dor el Gussa in the central-western parts of the country and are also encountered in deep exploration wells, especially in the Sirt Basin area, central Libya. Relatively fresh intraformational igneous rocks as well as those altered pose a problem of identification as to whether the material represents true basement or transitional horizons. Moreover, there are instances where regolithic basement or younger igneous rocks mimic semi- consolidated or friable sandstone. In the oil industry, it is imperative that drilling operations be cost effective, and if this is to be so, there must be a clear understanding of the nature of igneous rocks that are being penetrated and whether basement is reached or being drilled through.