Players — O
- Christian Montes De Oca 2025–2025
- Bryce Montes de Oca 2022–2022
- Mike O'Berry 1979–1985
- Billy O'Brien 1884–1890
- Bob O'Brien 1971–1971
- Buck O'Brien 1911–1913
- Charlie O'Brien 1985–2000
- Cinders O'Brien 1888–1891
- Dan O'Brien 1978–1979
- Darby O'Brien 1887–1892
- Dink O'Brien 1923–1923
- Eddie O'Brien 1953–1958
- George O'Brien 1915–1915
- Jack O'Brien 1899–1903
- Jack O'Brien 1882–1890
- John O'Brien 1884–1884
- John O'Brien 1891–1899
- Johnny O'Brien 1953–1959
- Pete O'Brien 1901–1907
- Pete O'Brien 1887–1890
- Pete O'Brien 1982–1993
- Peter O'Brien 2015–2019
- Ray O'Brien 1916–1916
- Riley O'Brien 2021–2025
- Syd O'Brien 1969–1972
- Tom O'Brien 1882–1890
- Tom O'Brien 1897–1900
- Tommy O'Brien 1943–1950
- Willie O'Bryant 1932–1932
- Danny O'Connell 1950–1962
- Jimmy O'Connell 1923–1924
- John O'Connell 1928–1929
- John O'Connell 1891–1902
- Pat O'Connell 1886–1886
- Andy O'Connor 1908–1908
- Brian O'Connor 2000–2000
- Dan O'Connor 1890–1890
- Frank O'Connor 1893–1893
- Jack O'Connor 1981–1987
- Jack O'Connor 1887–1910
- Johnny O'Connor 1916–1916
- Mike O'Connor 2006–2011
- Paddy O'Connor 1908–1918
- Darren O'Day 2008–2022
- Hank O'Day 1884–1890
- Ken O'Dea 1935–1946
- Paul O'Dea 1944–1945
- Billy O'Dell 1954–1967
- George O'Donnell 1954–1954
- Harry O'Donnell 1927–1927
- John O'Donnell 1884–1884
- John O'Donoghue 1993–1993
- John O'Donoghue 1963–1971
- Lefty O'Doul 1919–1934
- Bob O'Farrell 1915–1935
- Eric O'Flaherty 2006–2017
- Brian O'Grady 2019–2021
- Chris O'Grady 2017–2018
- Hal O'Hagan 1892–1902
- Greg O'Halloran 1994–1994
- Bill O'Hara 1909–1910
- Kid O'Hara 1904–1904
- Tom O'Hara 1906–1907
- Ryan O'Hearn 2018–2025
- Logan O'Hoppe 2022–2025
- Brian O'Keefe 2022–2023
- okeef01 1922–1922
- Charley O'Leary 1904–1934
- Dan O'Leary 1879–1884
- Troy O'Leary 1993–2003
- Jack O'Loughlin 2024–2024
- Patrick O'Loughlin 1883–1883
- Ryan O'Malley 2006–2006
- Shawn O'Malley 2014–2016
- Tom O'Malley 1982–1990
- Ollie O'Mara 1912–1919
- Eddie O'Meara 1895–1896
- Luther O'Neal 1910–1914
- Oran O'Neal 1925–1927
- Randy O'Neal 1984–1990
- Buck O'Neil 1937–1948
- Charles O'Neil 1921–1923
- Ed O'Neil 1890–1890
- Fancy O'Neil 1874–1874
- John O'Neil 1946–1946
- John O'Neil 1899–1902
- Mickey O'Neil 1919–1927
- Dennis O'Neill 1893–1893
- Emmett O'Neill 1943–1946
- Fred O'Neill 1887–1887
- Harry O'Neill 1939–1939
- Harry O'Neill 1922–1923
- Hugh O'Neill 1875–1875
- Jack O'Neill 1902–1906
- Jim O'Neill 1920–1923
- John O'Neill 1904–1906
- Mike O'Neill 1901–1907
- Paul O'Neill 1985–2001
- Peaches O'Neill 1904–1904
- Steve O'Neill 1911–1928
- Tip O'Neill 1883–1892
- Tyler O'Neill 2018–2025
- Don O'Riley 1969–1970
- Frank O'Rourke 1912–1931
- Jim O'Rourke 1872–1904
- Jim O'Rourke 1959–1959
- Jimmy O'Rourke 1908–1908
- Joe O'Rourke 1929–1929
- John O'Rourke 1879–1883
- Mike O'Rourke 1890–1890
- Patsy O'Rourke 1908–1908
- Ryan O'Rourke 2015–2019
- Tim O'Rourke 1890–1894
- Tom O'Rourke 1887–1890
- orour01 1872–1872
- Sean O'Sullivan 2009–2016
- Denny O'Toole 1969–1973
- Jim O'Toole 1958–1967
- Marty O'Toole 1908–1914
- Rebel Oakes 1909–1915
- Charles Oakley 1940–1940
- Trevor Oaks 2018–2018
- Prince Oana 1934–1945
- Johnny Oates 1970–1981
- Sherman Obando 1993–1997
- Bailey Ober 2021–2025
- Henry Oberbeck 1883–1884
- Scott Oberg 2015–2019
- Brett Oberholtzer 2013–2016
- Ken Oberkfell 1977–1992
- Doc Oberlander 1888–1888
- Frank Oberlin 1906–1910
- Wes Obermueller 2002–2007
- Jim Obradovich 1978–1978
- Alex Ochoa 1995–2002
- Ivan Ochoa 2008–2008
- Whitey Ock 1935–1935
- Walter Ockey 1944–1944
- Johnnie Oden 1927–1932
- Ted Odenwald 1921–1922
- Blue Moon Odom 1964–1976
- Dave Odom 1943–1943
- Heinie Odom 1925–1925
- Joseph Odom 2020–2021
- Sam Odom 1946–1946
- Rougned Odor 2014–2023
- Jake Odorizzi 2012–2022
- Fred Odwell 1904–1907
- Bryan Oelkers 1983–1986
- Trent Oeltjen 2009–2011
- Chuck Oertel 1958–1958
- Joe Oeschger 1914–1925
- Ron Oester 1978–1990
- Jose Offerman 1990–2005
- Rowland Office 1972–1983
- Mose Offutt 1925–1925
- Alexi Ogando 2010–2018
- Cristofer Ogando 2022–2022
- Nefi Ogando 2015–2016
- Shinnosuke Ogasawara 2025–2025
- Curly Ogden 1922–1926
- Jack Ogden 1918–1932
- Chad Ogea 1994–1999
- Jim Oglesby 1936–1936
- Ben Oglivie 1971–1986
- Bruce Ogrodowski 1936–1937
- Joe Ogrodowski 1925–1925
- Seunghwan Oh 2016–2019
- Tomo Ohka 1999–2009
- Joe Ohl 1909–1909
- Pierson Ohl 2025–2025
- Ross Ohlendorf 2007–2016
- Mike Ohlman 2017–2017
- Will Ohman 2000–2012
- Kevin Ohme 2003–2003
- Shohei Ohtani 2018–2025
- Kirt Ojala 1997–1999
- Augie Ojeda 2000–2010
- Bob Ojeda 1980–1994
- Miguel Ojeda 2003–2006
- Hideki Okajima 2007–2013
- Steven Okert 2016–2025
- Chris Okey 2022–2023
- Frank Okrie 1920–1920
- Len Okrie 1948–1952
- Jim Olander 1991–1991
- Pedro Olave 1906–1906
- Dave Oldfield 1883–1886
- Jimmy Oldham 1920–1923
- John Oldham 1956–1956
- Red Oldham 1914–1926
- Bob Oldis 1953–1963
- Rube Oldring 1905–1918
- John Olerud 1989–2005
- Frank Olin 1884–1885
- Steve Olin 1989–1992
- Jared Oliva 2020–2021
- Jose Oliva 1994–1995
- Tony Oliva 1962–1976
- Ed Olivares 1960–1961
- Edward Olivares 2020–2024
- Omar Olivares 1990–2001
- Al Oliver 1968–1985
- Andy Oliver 2010–2011
- Bob Oliver 1965–1975
- Darren Oliver 1993–2013
- Dave Oliver 1977–1977
- Gene Oliver 1959–1969
- Jim Oliver 1946–1946
- Joe Oliver 1989–2001
- John Henry Oliver 1930–1945
- Nate Oliver 1963–1969
- Tom Oliver 1930–1933
- Hector Olivera 2015–2016
- Francisco Oliveras 1989–1992
- Lester Oliveros 2011–2014
- Chi-Chi Olivo 1961–1966
- Diomedes Olivo 1960–1963
- Miguel Olivo 2002–2014
- Adam Oller 2022–2024
- Jim Ollom 1966–1967
- Ray Olmedo 2003–2012
- Luis Olmo 1943–1951
- Edgar Olmos 2013–2015
- Fred Olmstead 1908–1911
- Al Olmsted 1980–1980
- Hank Olmsted 1905–1905
- Barney Olsen 1941–1941
- Kevin Olsen 2001–2003
- Ole Olsen 1922–1923
- Scott Olsen 2005–2010
- Vern Olsen 1939–1946
- Garrett Olson 2007–2012
- Greg Olson 1989–1993
- Gregg Olson 1988–2001
- Ivy Olson 1911–1924
- Karl Olson 1951–1957
- Marv Olson 1931–1933
- Matt Olson 2016–2025
- Reese Olson 2023–2025
- Ted Olson 1936–1938
- Tim Olson 2004–2005
- Tyler Olson 2015–2019
- Mike Olt 2012–2015
- Ed Olwine 1986–1988
- omead01 1932–1932
- Brian Omogrosso 2012–2013
- Alejandro Oms 1917–1935
- Jorge Ona 2020–2020
- Logan Ondrusek 2010–2016
- Manuel Onis 1935–1935
- Eddie Onslow 1912–1927
- Jack Onslow 1912–1917
- Steve Ontiveros 1973–1980
- Steve Ontiveros 1985–2000
- Jose Oquendo 1983–1995
- Mike Oquist 1993–1999
- Tom Oran 1875–1875
- Grady Orange 1925–1931
- orang01 1928–1928
- Ernie Oravetz 1955–1956
- Luis Ordaz 1997–2006
- Tony Ordenana 1943–1943
- Magglio Ordonez 1997–2011
- Rey Ordonez 1996–2004
- Joe Orengo 1939–1945
- Nate Orf 2018–2020
- Kevin Orie 1997–2002
- Paulo Orlando 2015–2018
- Clarence Orme 1920–1920
- George Orme 1920–1920
- Jess Orndorff 1907–1907
- Jonathan Ornelas 2023–2025
- Tirso Ornelas 2025–2025
- Eddie Oropesa 2001–2004
- Jesse Orosco 1979–2003
- Billy Orr 1913–1914
- Dave Orr 1883–1890
- Pete Orr 2005–2013
- Joe Orrell 1943–1945
- Ernie Orsatti 1927–1935
- John Orsino 1961–1967
- Joe Orsulak 1983–1997
- Kaleb Ort 2021–2025
- Jorge Orta 1972–1987
- Anthony Ortega 2009–2009
- Bill Ortega 2001–2001
- Jose Ortega 2012–2014
- Oliver Ortega 2021–2023
- Phil Ortega 1960–1969
- Rafael Ortega 2012–2024
- Frank Ortenzio 1973–1973
- Al Orth 1895–1909
- Danny Ortiz 2017–2017
- David Ortiz 1997–2016
- Hector Ortiz 1998–2002
- Javier Ortiz 1990–1991
- Joe Ortiz 2013–2013
- Joey Ortiz 2023–2025
- Jose Ortiz 1969–1971
- Jose Ortiz 2000–2002
- Junior Ortiz 1982–1994
- Luis Ortiz 2022–2025
- Luis Ortiz 1993–1996
- Luis Ortiz 2018–2024
- Oliverio Ortiz 1944–1944
- Rafaelito Ortiz 1948–1948
- Ramon Ortiz 1999–2013
- Roberto Ortiz 1941–1950
- Russ Ortiz 1998–2010
- Daniel Ortmeier 2005–2008
- John Orton 1989–1993
- Chad Orvella 2005–2007
- Ossie Orwoll 1928–1929
- Eric Orze 2024–2025
- Bob Osborn 1925–1931
- Fred Osborn 1907–1909
- Ozzie Osborn 1975–1975
- Bobo Osborne 1957–1963
- Donovan Osborne 1992–2004
- Fred Osborne 1890–1890
- Tiny Osborne 1922–1925
- Wayne Osborne 1935–1936
- Pat Osburn 1974–1975
- Charlie Osgood 1944–1944
- Josh Osich 2015–2021
- Keith Osik 1996–2005
- Dan Osinski 1962–1970
- Julius Osley 1937–1938
- Franquelis Osoria 2005–2008
- Harry Ostdiek 1904–1908
- Champ Osteen 1903–1909
- Claude Osteen 1957–1975
- Darrell Osteen 1965–1970
- Fred Ostendorf 1914–1914
- Bill Oster 1954–1954
- Red Ostergard 1921–1921
- Charlie Osterhout 1879–1879
- Fritz Ostermueller 1934–1948
- Jimmy Osting 2001–2002
- Brian Ostrosser 1973–1973
- Joe Ostrowski 1948–1952
- Johnny Ostrowski 1943–1950
- Al Osuna 1990–1996
- Alejandro Osuna 2025–2025
- Antonio Osuna 1995–2005
- Jose Osuna 2017–2020
- Roberto Osuna 2015–2020
- Corey Oswalt 2018–2021
- Roy Oswalt 2001–2013
- Willis Otanez 1998–1999
- Michel Otañez 2024–2025
- Dan Otero 2012–2019
- Reggie Otero 1945–1945
- Ricky Otero 1995–1997
- Bill Otey 1907–1911
- Amos Otis 1967–1984
- Bill Otis 1912–1912
- Harry Otis 1909–1909
- Akinori Otsuka 2004–2007
- Billy Ott 1962–1964
- Ed Ott 1974–1981
- Mel Ott 1926–1947
- Adam Ottavino 2010–2025
- Jim Otten 1974–1981
- John Otten 1895–1895
- Billy Otterson 1887–1887
- Dave Otto 1987–1994
- Glenn Otto 2021–2023
- Phil Ouellette 1986–1986
- Johnny Oulliber 1933–1933
- Guy Ousley 1931–1932
- Bill Outen 1933–1933
- Jimmy Outlaw 1937–1949
- James Outman 2022–2025
- Josh Outman 2008–2014
- Orval Overall 1905–1913
- Lyle Overbay 2001–2014
- Stubby Overmire 1943–1952
- Albert Overton 1932–1944
- Connor Overton 2021–2023
- Dillon Overton 2016–2017
- Mike Overy 1976–1976
- Johan Oviedo 2020–2025
- Juan Carlos Oviedo 2005–2014
- Luis Oviedo 2021–2021
- Ernie Ovitz 1911–1911
- Bob Owchinko 1976–1986
- Dave Owen 1983–1988
- Frank Owen 1901–1909
- Hunter Owen 2021–2021
- Larry Owen 1981–1988
- Marv Owen 1931–1940
- Mickey Owen 1937–1954
- Spike Owen 1983–1995
- Albert Owens 1930–1930
- Aubrey Owens 1922–1925
- Dewitt Owens 1926–1930
- Eric Owens 1995–2003
- Henry Owens 2015–2016
- Henry Owens 2006–2007
- Jack Owens 1935–1935
- Jayhawk Owens 1993–1996
- Jerry Owens 2006–2009
- Jim Owens 1955–1967
- Judge Owens 1943–1943
- Oscar Owens 1922–1931
- Red Owens 1899–1905
- Roosevelt Owens 1934–1937
- Rudy Owens 2014–2014
- Smoky Owens 1938–1942
- Sylvester Owens 1937–1942
- Tyler Owens 2025–2025
- Will Owens 1924–1933
- Yip Owens 1905–1915
- Chris Owings 2013–2023
- Micah Owings 2007–2012
- Rick Ownbey 1982–1986
- Henry Oxley 1884–1884
- Chris Oxspring 2005–2005
- Andy Oyler 1902–1902
- Ray Oyler 1965–1970
- Horace Ozmer 1923–1923
- Marcell Ozuna 2013–2025
- Pablo Ozuna 2000–2008
- Dave Von Ohlen 1983–1987