Río de Oro (Spanish for "Gold River", Arabic: وادي الذهب wādī-að-ðahab, often transliterated as Oued Edhahab), is, with Saguia el-Hamra, one of the two territories that formed the Spanish province of Spanish Sahara after 1969; it was originally taken as a Spanish colonial possession in the late 19th century. Its name seems to come from an east-west river which was supposed to have run through it formerly. The river was thought to have largely dried out - a wadi, as the name indicates - or have disappeared underground.

However, deriving from its previous name Rio do Ouro Portuguese seafarers applied it to the area, although no gold had been found there, neither in the water of the narrow gulf, probably mistaken for the river itself, nor in its neighbourhood.

Occupying the southern part of Western Sahara, the territory lies between 26° to the north and 21° 20' to the south. The area is roughly 71,042 mi.² (184,000 km²), making it approximately two-thirds of the entire territory. The former provincial capital founded by the Spanish colonizers was Villa Cisneros, while the town's name under Moroccan administration has become ad-Dakhla .