The following is a list of Major League Baseball players, retired or active. As of the end of the 2011 season, there have been 320 players with a last name that begins with O who have been on a major league roster at some point.
O Name Debut Final game Position Teams RefMike O'Berry April 8, 1979 October 4, 1985 Catcher Boston Red Sox, Chicago Cubs, Cincinnati Reds, California Angels, New York Yankees, Montreal Expos Billy O'Brien September 27, 1884 October 3, 1890 First baseman St. Paul Saints, Kansas City Cowboys (UA), Washington Nationals (1886–1889), Brooklyn Gladiators Bob O'Brien April 11, 1971 July 7, 1971 Pitcher Los Angeles Dodgers Buck O'Brien September 9, 1911 August 6, 1913 Pitcher Boston Red Sox, Chicago White Sox Charlie O'Brien June 2, 1985 June 21, 2000 Catcher Oakland Athletics, Milwaukee Brewers, New York Mets, Atlanta Braves, Toronto Blue Jays, Chicago White Sox, Anaheim Angels, Montreal Expos Cinders O'Brien June 23, 1888 October 2, 1891 Pitcher Cleveland Blues, Cleveland Spiders, Cleveland Infants, Boston Reds (AA) Dan O'Brien September 4, 1978 September 28, 1979 Pitcher St. Louis Cardinals Darby O'Brien April 16, 1887 October 15, 1892 Outfielder New York Metropolitans, Brooklyn Bridegrooms/Grooms Dink O'Brien April 26, 1923 September 15, 1923 Catcher Philadelphia Phillies Eddie O'Brien April 25, 1953 April 19, 1958 Shortstop Pittsburgh Pirates George O'Brien August 16, 1915 August 23, 1915 Catcher St. Louis Browns Jack O'Brien (C) May 2, 1882 September 16, 1890 Catcher Philadelphia Athletics (AA), Brooklyn Grays, Baltimore Orioles (AA) Jack O'Brien (OF) April 14, 1899 September 28, 1903 Outfielder Washington Senators (NL), Cleveland Blues (AL), Boston Americans John O'Brien (OF) April 19, 1884 May 31, 1884 Outfielder Baltimore Monumentals John O'Brien (2B) April 22, 1891 October 7, 1899 Second baseman Brooklyn Grooms, Chicago Colts, Louisville Colonels, Washington Senators (NL), Baltimore Orioles (NL), Pittsburgh Pirates Johnny O'Brien April 19, 1953 July 19, 1959 Second baseman Pittsburgh Pirates, St. Louis Cardinals, Milwaukee Braves Pete O'Brien (1890s 2B) August 2, 1887 June 16, 1890 Second baseman Washington Nationals (1886–1889), Chicago Colts Pete O'Brien (1900s 2B) September 21, 1901 October 2, 1907 Second baseman Cincinnati Reds, St. Louis Browns, Cleveland Naps, Washington Senators Pete O'Brien (1B) September 3, 1982 July 20, 1995 First baseman Texas Rangers, Cleveland Indians, Seattle Mariners Ray O'Brien June 27, 1916 July 12, 1916 Outfielder Pittsburgh Pirates Syd O'Brien April 15, 1969 October 1, 1972 Third baseman Boston Red Sox, Chicago White Sox, California Angels, Milwaukee Brewers Tom O'Brien (2B) June 14, 1882 July 28, 1890 Second baseman Worcester Ruby Legs, Baltimore Orioles (AA), Boston Reds (UA), New York Metropolitans, Rochester Broncos Tom O'Brien (OF) May 10, 1897 October 13, 1900 Outfielder Baltimore Orioles (NL), Pittsburgh Pirates, New York Giants Tommy O'Brien April 24, 1943 May 13, 1950 Outfielder Pittsburgh Pirates, Boston Red Sox, Washington Senators Danny O'Connell July 14, 1950 September 26, 1962 Second baseman Pittsburgh Pirates, Milwaukee Braves, New York/San Francisco Giants, Washington Senators (1961–1971) Jimmy O'Connell April 17, 1923 September 28, 1924 Outfielder New York Giants John O'Connell (2B) August 22, 1891 September 20, 1902 Second baseman Baltimore Orioles (AA), Detroit Tigers John O'Connell (C) August 16, 1928 October 6, 1929 Catcher Pittsburgh Pirates Pat O'Connell July 22, 1886 September 9, 1886 Outfielder Baltimore Orioles (AA) Andy O'Connor October 6, 1908 October 6, 1908 Pitcher New York Highlanders Brian O'Connor May 13, 2000 September 27, 2000 Pitcher Pittsburgh Pirates Dan O'Connor June 3, 1890 July 19, 1890 First baseman Louisville Colonels Frank O'Connor August 3, 1893 August 7, 1893 Pitcher Philadelphia Phillies Jack O'Connor (C) April 20, 1887 October 9, 1910 Catcher Cincinnati Red Stockings (AA), Columbus Solons, Cleveland Spiders, St. Louis Perfectos/Cardinals, Pittsburgh Pirates, New York Highlanders, St. Louis Browns Jack O'Connor (P) April 9, 1981 October 3, 1987 Pitcher Minnesota Twins, Montreal Expos, Baltimore Orioles Johnny O'Connor September 16, 1916 September 16, 1916 Catcher Chicago Cubs Michael O'Connor April 27, 2006 Pitcher Washington Nationals, New York Mets Paddy O'Connor April 17, 1908 July 22, 1918 Catcher Pittsburgh Pirates, St. Louis Cardinals, Pittsburgh Rebels, New York Yankees Darren O'Day March 31, 2008 Pitcher Los Angeles Angels of Anaheim, New York Mets, Texas Rangers Hank O'Day May 2, 1884 October 3, 1890 Pitcher Toledo Blue Stockings, Pittsburgh Alleghenys, Washington Nationals (1886–1889), New York Giants, New York Giants (PL) Ken O'Dea April 21, 1935 August 6, 1946 Catcher Chicago Cubs, New York Giants, St. Louis Cardinals, Boston Braves Paul O'Dea April 19, 1944 September 20, 1945 Outfielder Cleveland Indians Billy O'Dell June 20, 1954 September 12, 1967 Pitcher Baltimore Orioles, San Francisco Giants, Milwaukee/Atlanta Braves, Pittsburgh Pirates George O'Donnell April 18, 1954 July 25, 1954 Pitcher Pittsburgh Pirates Harry O'Donnell April 30, 1927 September 30, 1927 Catcher Philadelphia Phillies John O'Donnell July 16, 1884 July 16, 1884 Catcher Philadelphia Keystones John O'Donoghue (1960s P) September 29, 1963 June 22, 1971 Pitcher Kansas City Athletics, Cleveland Indians, Baltimore Orioles, Seattle Pilots, Milwaukee Brewers, Montreal Expos John O'Donoghue (1990s P) June 27, 1993 October 3, 1993 Pitcher Baltimore Orioles Lefty O'Doul April 29, 1919 September 30, 1934 Outfielder New York Yankees, Boston Red Sox, New York Giants, Philadelphia Phillies, Brooklyn Robins/Dodgers Bob O'Farrell September 5, 1915 September 23, 1935 Catcher Chicago Cubs, San Francisco Giants, St. Louis Cardinals, Cincinnati Reds Eric O'Flaherty August 16, 2006 Pitcher Seattle Mariners, Atlanta Braves Hal O'Hagan September 24, 1892 July 17, 1902 First baseman Washington Senators (NL), Chicago Orphans, New York Giants, Cleveland Bronchos Greg O'Halloran May 16, 1994 August 6, 1994 Catcher Florida Marlins Bill O'Hara April 15, 1909 May 8, 1910 Outfielder New York Giants, St. Louis Cardinals Kid O'Hara September 15, 1904 September 22, 1904 Outfielder Boston Beaneaters Tom O'Hara September 19, 1906 July 4, 1907 Outfielder St. Louis Cardinals Charley O'Leary April 14, 1904 September 30, 1934 Shortstop Detroit Tigers, St. Louis Cardinals, St. Louis Browns Dan O'Leary September 3, 1879 August 6, 1884 Outfielder Providence Grays, Boston Red Caps, Detroit Wolverines, Worcester Ruby Legs, Cincinnati Outlaw Reds Troy O'Leary May 9, 1993 September 28, 2003 Outfielder Milwaukee Brewers, Boston Red Sox, Montreal Expos, Chicago Cubs Ryan O'Malley August 16, 2006 August 22, 2006 Pitcher Chicago Cubs Tom O'Malley May 8, 1982 October 3, 1990 Third baseman San Francisco Giants, Chicago White Sox, Baltimore Orioles, Texas Rangers, Montreal Expos, New York Mets Ollie O'Mara September 8, 1912 April 19, 1919 Shortstop Detroit Tigers, Brooklyn Robins Tom O'Meara September 29, 1895 July 22, 1896 Catcher Cleveland Spiders Randy O'Neal September 12, 1984 October 2, 1990 Pitcher Detroit Tigers, Atlanta Braves, St. Louis Cardinals, Philadelphia Phillies, San Francisco Giants Skinny O'Neal April 18, 1925 May 27, 1927 Pitcher Philadelphia Phillies Denny O'Neil June 18, 1893 July 26, 1893 First baseman St. Louis Browns (NL) Ed O'Neil June 20, 1890 October 12, 1890 Pitcher Toledo Maumees, Philadelphia Athletics (AA) Fancy O'Neil October 23, 1874 October 23, 1874 Right fielder Hartford Dark Blues Hugh O'Neil August 20, 1875 October 9, 1875 Utility player Brooklyn Atlantics John O'Neil April 16, 1946 September 29, 1946 Shortstop Philadelphia Phillies Mickey O'Neil September 12, 1919 June 19, 1927 Catcher Boston Braves, Brooklyn Robins, Washington Senators, New York Giants Bill O'Neill May 7, 1904 October 7, 1906 Outfielder Boston Americans, Washington Senators, Chicago White Sox Emmett O'Neill August 3, 1943 June 5, 1946 Pitcher Boston Red Sox, Chicago Cubs, Chicago White Sox Fred O'Neill May 3, 1887 May 22, 1887 Outfielder New York Metropolitans Harry O'Neill (P) September 15, 1922 May 28, 1923 Pitcher Philadelphia Athletics Harry O'Neill (C) July 23, 1939 July 23, 1939 Catcher Philadelphia Athletics Jack O'Neill April 21, 1902 October 3, 1906 Catcher St. Louis Cardinals, Chicago Cubs, Boston Beaneaters Jim O'Neill April 15, 1920 July 29, 1923 Shortstop Washington Senators John O'Neill September 6, 1899 September 5, 1902 Catcher New York Giants Mike O'Neill September 20, 1901 October 6, 1907 Pitcher St. Louis Cardinals Paul O'Neill September 3, 1985 October 7, 2001 Outfielder Cincinnati Reds, New York Yankees Peaches O'Neill April 16, 1904 August 4, 1904 Catcher Cincinnati Reds Steve O'Neill September 18, 1911 September 14, 1928 Catcher Cleveland Naps/Indians, Boston Red Sox, New York Yankees, St. Louis Browns Tip O'Neill May 5, 1883 August 30, 1892 Outfielder New York Gothams, St. Louis Browns, Chicago Pirates, Cincinnati Reds Don O'Riley June 20, 1969 August 1, 1970 Pitcher Kansas City Royals O'Rourke, first name unknown July 9, 1872 July 9, 1872 Pitcher Eckford of Brooklyn Charlie O'Rourke June 16, 1959 June 16, 1959 Pinch hitter St. Louis Cardinals Frank O'Rourke June 12, 1912 July 28, 1931 Third baseman Boston Braves, Brooklyn Robins, Washington Senators, Boston Red Sox, Detroit Tigers, St. Louis Browns Jim O'Rourke β April 26, 1872 September 22, 1904 Outfielder Middletown Mansfields, Boston Red Stockings/Red Caps, Providence Grays, Buffalo Bisons (NL), New York Giants, New York Giants (PL), Washington Senators (NL) Jimmy O'Rourke August 15, 1908 October 8, 1908 Utility player New York Highlanders Joe O'Rourke April 19, 1929 June 5, 1929 Pinch hitter Philadelphia Phillies John O'Rourke May 1, 1879 September 10, 1883 Outfielder Boston Red Caps, New York Metropolitans Mike O'Rourke September 1, 1890 October 15, 1890 Pitcher Baltimore Orioles (AA) Patsy O'Rourke April 16, 1908 July 12, 1908 Shortstop St. Louis Cardinals Tim O'Rourke May 27, 1890 August 7, 1894 Utility player Syracuse Stars (AA), Columbus Solons, Baltimore Orioles (NL), Louisville Colonels, St. Louis Browns (NL), Washington Senators (NL) Tom O'Rourke May 11, 1887 August 1, 1890 Catcher Boston Beaneaters, New York Giants, Syracuse Stars (AA) Sean O'Sullivan June 16, 2009 Pitcher Los Angeles Angels of Anaheim, Kansas City Royals Dennis O'Toole September 8, 1969 June 23, 1973 Pitcher Chicago White Sox Jim O'Toole September 26, 1958 July 22, 1967 Pitcher Cincinnati Redlegs/Reds, Chicago White Sox Marty O'Toole September 21, 1908 October 6, 1914 Pitcher Cincinnati Reds, Pittsburgh Pirates, New York Giants Rebel Oakes April 14, 1909 October 3, 1915 Outfielder Cincinnati Reds, St. Louis Cardinals, Pittsburgh Rebels Prince Oana April 22, 1934 September 18, 1945 Pitcher Philadelphia Phillies, Detroit Tigers Johnny Oates September 17, 1970 May 24, 1981 Catcher Baltimore Orioles, Atlanta Braves, Philadelphia Phillies, Los Angeles Dodgers, New York Yankees Sherman Obando April 10, 1993 July 21, 1997 Outfielder Baltimore Orioles, Montreal Expos Henry Oberbeck May 7, 1883 October 18, 1884 Outfielder Pittsburgh Alleghenys, St. Louis Browns (AA), Baltimore Monumentals, Kansas City Cowboys (UA) Ken Oberkfell August 22, 1977 October 4, 1992 Third baseman St. Louis Cardinals, Atlanta Braves, Pittsburgh Pirates, San Francisco Giants, Houston Astros, California Angels Doc Oberlander May 16, 1888 June 2, 1888 Pitcher Cleveland Blues (AA) Frank Oberlin September 20, 1906 June 28, 1910 Pitcher Boston Red Sox, Washington Senators Wes Obermueller September 20, 2002 July 13, 2007 Pitcher Kansas City Royals, Milwaukee Brewers, Florida Marlins Jim Obradovich September 12, 1978 September 29, 1978 First baseman Houston Astros Alex Ochoa September 18, 1995 September 29, 2002 Outfielder New York Mets, Minnesota Twins, Milwaukee Brewers, Cincinnati Reds, Colorado Rockies, A