Western Siberia or West Siberia (Russian: Западная Сибирь, romanized: Zapadnaya Sibir'; Kazakh: Батыс Сібір) is a part of the larger region of Siberia that is mostly located in the Russian Federation. It lies between the Ural region and the Yenisei River, which conventionally divides Siberia into two halves.
Western Siberia covers an area of 2,500,000 square kilometers (970,000 sq mi), nearly 80% of which is located within the West Siberian Plain. The largest rivers of the region are the Irtysh and the Ob.
The West Siberian petroleum basin is the largest hydrocarbon (petroleum and natural gas) basin in the world covering an area of about 2.2 million km2, and is also the largest oil and gas producing region in Russia.
In medieval times, the region was part of the Golden Horde. After its gradual decline during the 15th century, the Khanate of Sibir, centered on Tyumen, was formed within the area. In the late 16th century, most of Western Siberia was conquered by the Russian Empire, while its southern region became part of the Kazakh Khanate. The current international borders between Russia and Kazakhstan came into being in the late 20th century following the dissolution of the Soviet Union.
The most populous city of Western Siberia is Novosibirsk. Other major cities include: