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- The O.C. (2003–2007), teen drama
- The Oblongs (2001–2002), animated comedy
- Ocean Ave. (2002–2003), soap opera
- October Road (2007–2008), comedy
- The Odd Couple (1970–1975), sitcom
- Odd Man Out (1999–2000), sitcom
- Off Centre (2001–2002), sitcom
- Off the Map (2011), medical drama
- Off the Rack (1984–1985), sitcom
- The Office (March 24, 2005 – present), comedy
- Oh Baby (1998–2000), sitcom
- Oh, Grow Up (1999), sitcom
- Oh Madeline (1983–1984), sitcom
- Ohara (1987–1988), crime drama
- O'Hara, U.S. Treasury (1971–1972), crime drama
- The O'Keefes (2003), sitcom
- The Oldest Rookie (1987–1988), crime drama
- Oliver Beene (2003–2004), sitcom
- On Our Own (1977–1978), sitcom
- On Our Own (1994–1995), sitcom
- On the Air (1992), sitcom
- On the Rocks (1975–1976), sitcom
- On the Spot (2003), sitcom
- Once a Hero (1987), science fiction/ sitcom
- Once and Again (1999–2002), drama
- Once Upon a Time (2011–present), fantasy
- One Day at a Time (1975–1984), sitcom
- One Life to Live (1968–2012), soap opera
- One On One (2001–2006), sitcom
- One Step Beyond (1959–1961), mystery horror anthology
- One Tree Hill (September 23, 2003 – present), teen drama
- One West Waikiki (1994–1996), crime drama
- One World (1998–2001), teen sitcom
- Open House (1989–1990), sitcom
- Operation Petticoat (1977–1979), sitcom
- Opposite Sex (2000), sitcom
- The Oprah Winfrey Show (1986–2011), talk show
- The Oregon Trail (1977), western
- The O'Reilly Factor (October 7, 1996 – present), talk show
- Orleans (1997), drama
- The Osbournes (2002–2005), reality
- Over There (2005),war
- Others (2000), sci-fi
- Our Family Honor (1985–1986), drama
- Our House (1986–1988), drama
- Our World (1986–1987), documentary
- Outlaws (1986), cowboy drama
- The Outer Limits (1995–2002), sci-fi
- Out of Control (1984–1988), children's talk show
- Out of this World (1987–1991), sitcom
- Outsourced (2010–2011), sitcom
- Oz (1997–2003), prison drama
Read more about this topic: List Of American Television Series