The Tertiary Gabes basin is located offshore of Tunisia and Libya and is bounded on the north by the Kerkenna high and Pantelleria rift zone, on the east by the offshore extension of the Sirte basin, on the south by the Djeffara fault zone, and on the west by the Tunisian north-south axis.

The most prospective sedimentary rocks in the Gulf of Gabes are those of the lower Eocene and Upper Cretaceous. The lower Eocene Metlaoui Formation (50 to 180 m thick) is the main producing interval in the Gabes basin and is productive in the Sidi Itayem field, Sidi Behara field, Ashtart field, Hasdrubal, Didon, A1-137, and B1-137. In these areas, the Metlaoui Formation is characterized by a nummulitic facies. In general, the Metlaoui Formation grades from a coquinoid facies in the southwest to a nummulitic facies near the center of the basin to a globigerinid facies in the northeast.

The Maestrichtian-Paleocene El Haria Formation underlying the Metlaoui consists of approximately 150 m of shale and is considered to be the major source rock in the Gabes basin.

Underlying the El Haria is the Mizda Formation (Campanian-Turonian), a shaly limestone approximately 400 m thick. Wet gas was found in the lower Mizda Formation in wells Miskar 1 and 2.

The Nefusa Group (450 m thick) is of Cenomanian age and underlies the Mizda. It is composed of marlstone, limestone, and dolomite. Reefal development within this group provides the reservoir for the Isis oil field, Elyssa-1 gas well, and Didon-1 oil well.

Although the Upper Cretaceous and lower Eocene are the major exploration objectives in the Gabes basin, data from onshore outcrop studies in Tunisia and Libya indicate excellent reservoir potential in Jurassic, Lower Cretaceous, and Oligocene rocks.

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