Mare Vaporum (Latin vapōrum, the "sea of vapors") is a lunar mare located between the southwest rim of Mare Serenitatis and the southeast rim of Mare Imbrium. It was named by Giovanni Battista Riccioli in 1651. The mare lies in an old basin or crater that is within the Procellarum basin. It is 242 km in diameter and 55000 km2 in area, and is bordered to the northeast by the mountain range Montes Apenninus. In the south of the mare is Rima Hyginus, a rille intersected by the crater Hyginus. The lunar material surrounding the mare is from the Lower Imbrian epoch, and the mare material is from the Eratosthenian epoch.