a river in Orenburg and Kuibyshev oblasts, RSFSR; a left tributary of the Volga. The Sok is 364 km long and drains an area of 11,700 sq km. It originates in the Bugul’ma-Belebei Elevation and is fed mainly by snow. High water is from April to early May. The mean flow rate 174 km from the mouth is 16.1 cu m per sec. The Sok freezes between late October and early December, and the ice breaks up in April. The Kondurcha River is a right tributary of the Sok. The Sok is navigable in its lower course.