Administratively, the Oberaargau forms a district within the region Emmental-Oberaargau of the canton of Bern. Historically (until 2009), the Oberaargau comprised the two administrative districts of Wangen and Aarwangen.
It lies in the extreme northeast corner of the canton and includes the districts of Aarwangen and Wangen, and part of the district of Trachselwald. It is surrounded by the cantons of Solothurn, Aargau, and Lucerne. It is connected to the rest of the canton of Bern only in the south, where it borders on the Emmenthal.
The Oberaargau lies on the Swiss Plateau between the large population centers of Bern and Zürich and has therefore become a major thoroughfare for traffic running both east and west and north and south. The Aar River traverses it from west to east, and the primary motorway of Switzerland (the A1) and the main Bern-Zürich railway run through it, making it a central transport region.
The primary city is Langenthal, and the towns of Herzogenbuchsee, Wangen, and Aarwangen are important transportation centers. Since the building of the motorway, the primary economic development has taken place in the north, at the foot of the Jura Mountains, particularly in the towns of Wiedlisbach and Niederbipp.