The Oca river is a short river, about 70 kilometres (43 mi) long, in the north of Spain. It is an affluent of the Ebro river that flows through the province of Burgos. It begins in the Sistema Ibérico range and flows north through the municipalities of Rábanos, Villafranca Montes de Oca, Valle de Oca, Alcocero de Mola, Prádanos de Bureba, Briviesca, Vileña, the shire of Bureba and Oña.