From the early 1970s to the mid-1990s Óscar Castro was one of the leading Colombian chess players. He won the Colombian Chess Championships 6 times: 1972–1974, 1992, 1994, 1999. In 1976 in Biel, Óscar Castro participated in the World Chess Championship Interzonal Tournament where he ranked in 18th place. In this tournament he beat such chess grandmasters as Tigran Petrosian and Efim Geller.