The West Siberian Plain (За́падно-Сиби́рская равни́на) is a large plain that occupies the western portion of Siberia and Russia, between the Ural Mountains in the west and the Yenisei River in the east, and by the Eastern Sayan Mountains and the Baikal Mountains on the south. It has been described as the world's largest unbroken lowland—more than 50 percent is less than 330 feet (101 m) above sea level—and covers an area of about 2.6–2.7 million km² which is about one third of Siberia, extending from north to south for 2,400 km, from the Arctic Ocean to the foothills of the Altay Mountains, and from west to east for 1,900 km from the Yenisei River to the Ural Mountains. The plain has eight distinct vegetation regions: tundra, forest-tundra, northern taiga, middle taiga, southern taiga, sub-taiga forest, forest-steppe, and steppe. The number of animal species in the West Siberian Plain ranges from at least 107 in the tundra to 278 or more in the forest-steppe region.
It is one of the world's largest areas of peatlands, which are characterized by raised bogs. It is believed that the world’s largest single raised bog is at Vasuganskoe, covering approximately 51,600 km².
Large regions of the plains are flooded in the spring, and marshlands make much of the area unsuitable for agriculture. The principal rivers in the West Siberian Plain are the Ob, Irtysh, and Yenisei. There are many lakes and swamps, as well as large petroleum and natural gas reserves. Most of the Russia's oil and gas production was extracted from this area during the 1970s and 80s.