The Po Plain, from a geological point of view, may be divided in two regions—the Periapenninic trough in the south and the Pedealpine region in the north.
The Periapenninic trough is featured by a continuous sedimentation from Oligocene to Quaternary and by a tremendous thickness of clays, marls, and sandy sediments, mainly of a neritic facies. In this trough the Miocene and the Pliocene formations are folded with long and regular anticlines, whereas the Quaternary is subhorizontal.
In the Pedealpine region the basement is not so deep as in the Periapenninic trough and the Pliocene is trasgressive on the middle Miocene or older formations. The pre-Pliocene formations are strongly deformed and eroded, but the Pliocene is only mildly folded, locally above buried hills.
Hydrocarbon shows, mostly gas, have been found in all the sedimentary series, drilled from Quaternary to Oligocene. However, commercial pools have been found only on the tops of the anticlines, from lower Quaternary (Correggio beds) to Tortonian (Cortemaggiore beds).
We presume that most of the hydrocarbons have accumulated on top of the anticlines by migration from the flanks rather than from vertical migration.
AGIP Mineraria has found thirteen main gas fields (one with oil) and some others of little importance.
Only eight of the eleven fields are actually producing, with an average daily rate of 10 million cubic meters (350 million cubic feet) of gas. A further daily production of 800,000 cubic meters (28 million cubic feet) of gas, with salt water, is obtained from upper Quaternary in the eastern Po Plain, by many small private companies.