principal petroleum-producing (petroleum) region of Russia. Situated in the southern part of European Russia, it stretches from the west flank of the Ural Mountains to west of the Volga River. The largest fields are in Bashkortostan and Tatarstan and near Samara (Syzran fields), Perm, and Orenburg. Buguruslan has large natural-gas fields. Exploitation of the fields began in 1929. The name Second Baku was an allusion to the old oil fields around Baku in Azerbaijan. There are also many large oil refineries in the Volga-Ural region. A pipeline system, more than 3,000 miles (5,000 km) long, was built in 1960–64. A second parallel system having a greater diameter was constructed in the mid-1970s. It supplies the region's oil to Russian industrial centres and also connects to Poland, eastern Germany, Slovakia, Czech Republic, and Hungary.