Kuybyshev Reservoir or Kuybyshevskoye Reservoir (, Kuybyshevskoye Vodokhranilishche, ), sometimes called Samara Reservoir and informally called Kuybyshev Sea, is a reservoir of the middle Volga and lower Kama in the Chuvash Republic, Mari El Republic, Republic of Tatarstan, Samara Oblast and Ulyanovsk Oblast, Russia. The Kuybyshev Reservoir has a surface area of 6,450 km² and a volume of 58 billion cubic meters. It is the largest reservoir in Europe and third in the world by surface area. The major cities of Kazan, Ulyanovsk, and Tolyatti are adjacent to the reservoir.