- O'Hare Airport Chicago [13]
- O. J. Mayo [210]
- O. J. Simpson [27]
- Oak Brook, Illinois [6]
- Oaklahoma City Thunder [37]
- Oaklahoma Sooners [27]
- Oakland Athletics [250]
- Oakland Raiders [9]
- Oakland Raiders Team Players [15]
- Oakland Tribune [22]
- Oakland, California [79]
- Obstetrics And Gynaecology [5]
- The Office [7]
- Office Depot Inc. [8]
- Official Music Charts [16]
- OFWGKTA [9]
- Ohio [53]
- Ohio Cities [197]
- Ohio River [6]
- Ohio State Buckeyes [8]
- Ohio State University [168]
- Ohio Valley Conference [6]
- Okinawa Prefecture [7]
- Oklahoma [250]
- Oklahoma City [250]
- Oklahoma City Thunder [250]
- Old Trafford [8]
- Olindo Mare [12]
- Olive Garden [11]
- Oliver Ekman-Larsson [15]
- Óliver Pérez [9]
- Oliver Purnell [8]
- Oliver Stone [5]
- Olivia Wilde [10]
- Olivier Rochus [9]
- Olli Jokinen [24]
- Olli Rehn [5]
- Olympic Games [17]
- Olympic Summer Games [20]
- Omar Gonzalez [9]
- Omar Infante [34]
- Omar Strong [23]
- Omar Vizquel [10]
- Ömer Aşık [103]
- Omri Casspi [23]
- Oncor Electric Delivery [9]
- One Direction [10]
- The Onion [7]
- Online Gambling [7]
- Online Services [6]
- Online Shopping [5]
- Ontario Hockey League [6]
- OPEC [7]
- The Open Championship [43]
- Operas [12]
- Operating Systems [12]
- Oprah Winfrey [74]
- Oracle Arena [106]
- Oral Roberts [23]
- Orange Bowl [32]
- The Orange County Register [13]
- Orchestras [7]
- Order of Merit [5]
- Oregon [112]
- Oriole Park at Camden Yards [29]
- The Orioles [8]
- Orlando Cepeda [6]
- Orlando Magic [57]
- Orlando Magic Team [250]
- Orlando Salido [7]
- Orlando Scandrick [52]
- Osama bin Laden [31]
- Oscar De La Hoya [5]
- Oscar Mayer [5]
- Oscar Pistorius [74]
- Osi Umenyiora [17]
- Oswaldo Arcia [21]
- Otis Redding [8]
- Ottawa [82]
- Otto Graham [6]
- Outfielders [24]
- Outland Trophy [17]
- Overtime (sports) [142]
- Owen Daniels [10]
- Owings Mills, Maryland [8]
- OWN: Oprah Winfrey Network [7]
- Ozzie Guillén [14]
- Ozzie Newsome [81]
- Ozzy Osbourne [6]