KOST (103.5 FM, "KOST 103.5") is a radio station licensed to Los Angeles, California, with a Mainstream AC musical format. It is one of three Adult Contemporary-based formatted radio station in the Los Angeles/Orange County area, the others being sister station KBIG (Hot AC) and CBS-owned Smooth/Urban AC KTWV. The station is one of the top rated radio stations in Los Angeles and one of the top revenue billing radio stations in the United States.