All the important producing oil fields in Europe west of Russia are in the region of the Carpathian Mountains. They are a northern offshoot of the Alps beginning with the Little Carpathians 30 miles east of Vienna and extending in an arc through southern Poland and Rumania, crossing the Danube to bend eastward into the Balkan Mountains. Inside the arc are the Pannonian, Transylvanian, and smaller basins.

The major fields of Poland, the small pools in eastern Rumania, and the major fields of the Ploesti region in Rumania are on the outer fringe of the Carpathians; the large gas fields of Transylvania, and three fields in southwestern Hungary lie inside the arc, while the Austrian fields are outside.

Oil in the Vienna Basin fields is produced from upper Miocene (Sarmatian), from the Schlier (middle lower Miocene), and from Flysch, all associated with faulting along a buried Flysch ridge.

The major production in Poland is from Oligocene beds in complicated overthrust structures; the several unimportant fields in eastern Rumania occur mostly on overthrust structures in the Oligocene with minor Eocene and lower Miocene production; the south Rumania (Ploesti district) major fields, which account for 98 per cent of the country's oil, produce mainly from the Pliocene (Dacian and Meotian), with some Miocene and less Oligocene accumulation. In Rumanian fields salt has played an important part in the folding and faulting, with minor overthrusting. The great Transylvanian gas fields produce from Sarmatian on anticlinal structures. In southwest Hungary (Transdanubia) the major fields are found in normal anticlines, the accumulation being in lower Pliocene.