# List of Major League Baseball players (O)

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.

## List of Major League Baseball players

* A
* B
* C
* D
* E
* F
* G
* H
* I
* J
* K
* L
* M
* N
* O
* P
* Q
* R
* S
* T
* U
* V
* W
* X
* Y
* Z

## O

| Name | Debut | Final game | Position | Teams |
| Mike 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, Anaheim Angels |
| Iván Ochoa | July 12, 2008 | | Shortstop | San Francisco Giants |
| Whitey Ock | September 29, 1935 | September 29, 1935 | Catcher | Brooklyn Dodgers |
| Walter Ockey | May 3, 1944 | May 20, 1944 | Pitcher | New York Giants |
| Ted Odenwald | April 13, 1921 | April 21, 1922 | Pitcher | Cleveland Indians |
| Blue Moon Odom | September 5, 1964 | August 17, 1976 | Pitcher | Kansas City/Oakland Athletics, Cleveland Indians, Atlanta Braves, Chicago White Sox |
| Dave Odom | May 31, 1943 | September 13, 1943 | Pitcher | Boston Braves |
| Heinie Odom | April 22, 1925 | April 22, 1925 | Third baseman | New York Yankees |
| Fred Odwell | April 16, 1904 | September 12, 1907 | Outfielder | Cincinnati Reds |
| Bryan Oelkers | April 9, 1983 | October 3, 1986 | Pitcher | Minnesota Twins, Cleveland Indians |
| Trent Oeltjen | August 6, 2009 | | Outfielder | Arizona Diamondbacks, Los Angeles Dodgers |
| Chuck Oertel | September 1, 1958 | September 26, 1958 | Outfielder | Baltimore Orioles |
| Joe Oeschger | April 21, 1914 | September 6, 1925 | Pitcher | Philadelphia Phillies, New York Giants, Boston Braves, Philadelphia Phillies, Brooklyn Robins |
| Ron Oester | September 10, 1978 | October 3, 1990 | Second baseman | Cincinnati Reds |
| José Offerman | August 19, 1990 | October 2, 2005 | Utility infielder | Los Angeles Dodgers, Kansas City Royals, Boston Red Sox, Seattle Mariners, Minnesota Twins, Philadelphia Phillies, New York Mets |
| Rowland Office | August 5, 1972 | April 20, 1983 | Outfielder | Atlanta Braves, Montreal Expos, New York Yankees |
| Alexi Ogando | June 15, 2010 | | Pitcher | Texas Rangers |
| Curly Ogden | July 18, 1922 | July 21, 1926 | Pitcher | Philadelphia Athletics, Washington Senators |
| Jack Ogden | June 22, 1918 | September 9, 1932 | Pitcher | New York Giants, St. Louis Browns, Cincinnati Reds |
| Chad Ogea | May 3, 1994 | October 2, 1999 | Pitcher | Cleveland Indians, Philadelphia Phillies |
| Jim Oglesby | April 14, 1936 | April 17, 1936 | First baseman | Philadelphia Athletics |
| Ben Oglivie | September 4, 1971 | October 5, 1986 | Outfielder | Boston Red Sox, Detroit Tigers, Milwaukee Brewers |
| Bruce Ogrodowski | April 14, 1936 | October 3, 1937 | Catcher | St. Louis Cardinals |
| Joe Ogrodowski | April 27, 1925 | April 27, 1925 | Pitcher | Boston Braves |
| Tomo Ohka | July 19, 1999 | | Pitcher | Boston Red Sox, Montreal Expos, Washington Nationals, Milwaukee Brewers, Toronto Blue Jays, Cleveland Indians |
| Joe Ohl | July 29, 1909 | August 5, 1909 | Pitcher | Washington Senators |
| Ross Ohlendorf | September 11, 2007 | | Pitcher | New York Yankees, Pittsburgh Pirates |
| Will Ohman | September 19, 2000 | | Pitcher | Chicago Cubs, Atlanta Braves, Los Angeles Dodgers, Baltimore Orioles, Florida Marlins, Chicago White Sox |
| Kevin Ohme | April 14, 2003 | April 15, 2003 | Pitcher | St. Louis Cardinals |
| Kirt Ojala | August 18, 1997 | May 4, 1999 | Pitcher | Florida Marlins |
| Augie Ojeda | June 4, 2000 | | Utility infielder | Chicago Cubs, Minnesota Twins, Arizona Diamondbacks |
| Bob Ojeda | July 13, 1980 | April 22, 1994 | Pitcher | Boston Red Sox, New York Mets, Los Angeles Dodgers, Cleveland Indians, New York Yankees |
| Miguel Ojeda | May 17, 2003 | October 1, 2006 | Catcher | San Diego Padres, Seattle Mariners, Colorado Rockies, Texas Rangers |
| Hideki Okajima | April 2, 2007 | | Pitcher | Boston Red Sox |
| Frank Okrie | April 20, 1920 | August 4, 1920 | Pitcher | Detroit Tigers |
| Len Okrie | June 16, 1948 | April 16, 1952 | Catcher | Washington Senators, Boston Red Sox |
| Jim Olander | September 20, 1991 | October 5, 1991 | Outfielder | Milwaukee Brewers |
| Patrick O'Loughlin | May 9, 1883 | May 9, 1883 | Outfielder | Baltimore Orioles (AA) |
| Dave Oldfield | June 28, 1883 | October 11, 1886 | Catcher | Baltimore Orioles (AA), Brooklyn Grays, Washington Nationals (1886–1889) |
| John Oldham | September 2, 1956 | September 2, 1956 | Pinch runner | Cincinnati Redlegs |
| Red Oldham | August 19, 1914 | July 8, 1926 | Pitcher | Detroit Tigers, Pittsburgh Pirates |
| Bob Oldis | April 28, 1953 | September 29, 1963 | Catcher | Washington Senators, Pittsburgh Pirates, Philadelphia Phillies |
| Rube Oldring | October 2, 1905 | August 30, 1918 | Outfielder | New York Highlanders/Yankees, Philadelphia Athletics |
| John Olerud | September 3, 1989 | October 2, 2005 | First baseman | Toronto Blue Jays, New York Mets, Seattle Mariners, New York Yankees, Boston Red Sox |
| Frank Olin | July 4, 1884 | June 10, 1885 | Outfielder | Washington Nationals (AA), Washington Nationals (UA), Toledo Blue Stockings, Detroit Wolverines |
| Steve Olin | July 29, 1989 | October 4, 1992 | Pitcher | Cleveland Indians |
| José Oliva | July 1, 1994 | October 1, 1995 | Third baseman | Atlanta Braves, St. Louis Cardinals |
| Tony Oliva | September 9, 1962 | September 29, 1976 | Outfielder | Minnesota Twins |
| Ed Olivares | September 16, 1960 | September 26, 1961 | Outfielder | St. Louis Cardinals |
| Omar Olivares | August 18, 1990 | September 28, 2001 | Pitcher | St. Louis Cardinals, Colorado Rockies, Philadelphia Phillies, Detroit Tigers, Seattle Mariners, Anaheim Angels, Oakland Athletics, Pirates |
| Al Oliver | September 23, 1968 | October 5, 1985 | Outfielder | Pittsburgh Pirates, Texas Rangers, Montreal Expos, San Francisco Giants, Philadelphia Phillies, Los Angeles Dodgers, Toronto Blue Jays |
| Andrew Oliver | June 25, 2010 | | Pitcher | Detroit Tigers |
| Bob Oliver | September 10, 1965 | July 3, 1975 | First baseman | Pittsburgh Pirates, Kansas City Royals, California Angels, Baltimore Orioles, New York Yankees |
| Darren Oliver | September 1, 1993 | | Pitcher | Texas Rangers, St. Louis Cardinals, Boston Red Sox, Colorado Rockies, Florida Marlins, Houston Astros, New York Mets, Los Angeles Angels of Anaheim |
| Dave Oliver | September 25, 1977 | October 2, 1977 | Second baseman | Cleveland Indians |
| Gene Oliver | June 6, 1959 | August 24, 1969 | Utility player | St. Louis Cardinals, Milwaukee/Atlanta Braves, Philadelphia Phillies, Boston Red Sox, Chicago Cubs |
| Joe Oliver | July 15, 1989 | October 6, 2001 | Catcher | Cincinnati Reds, Milwaukee Brewers, Detroit Tigers, Seattle Mariners, New York Yankees, Boston Red Sox |
| Nate Oliver | April 9, 1963 | September 27, 1969 | Second baseman | Los Angeles Dodgers, San Francisco Giants, New York Yankees, Chicago Cubs |
| Tom Oliver | April 14, 1930 | September 23, 1933 | Outfielder | Boston Red Sox |
| Francisco Oliveras | May 3, 1989 | October 3, 1992 | Pitcher | Minnesota Twins, San Francisco Giants |
| Lester Oliveros | July 1, 2011 | | Pitcher | Detroit Tigers, Minnesota Twins |
| Chi-Chi Olivo | June 5, 1961 | October 1, 1966 | Pitcher | Milwaukee/Atlanta Braves |
| Diomedes Olivo | September 5, 1960 | June 12, 1963 | Pitcher | Pittsburgh Pirates, St. Louis Cardinals |
| Miguel Olivo | September 15, 2002 | | Catcher | Chicago White Sox, Seattle Mariners, San Diego Padres, Florida Marlins, Kansas City Royals, Colorado Rockies, Seattle Mariners |
| Jim Ollom | September 3, 1966 | September 15, 1967 | Pitcher | Minnesota Twins |
| Ray Olmedo | May 25, 2003 | | Shortstop | Cincinnati Reds, Toronto Blue Jays |
| Luis Olmo | July 23, 1943 | June 6, 1951 | Outfielder | Brooklyn Dodgers, Boston Braves |
| Fred Olmstead | July 2, 1908 | September 4, 1911 | Pitcher | Chicago White Sox |
| Al Olmsted | September 12, 1980 | October 3, 1980 | Pitcher | St. Louis Cardinals |
| Hank Olmsted | July 15, 1905 | July 26, 1905 | Pitcher | Boston Americans |
| Barney Olsen | April 17, 1941 | September 28, 1941 | Outfielder | Chicago Cubs |
| Kevin Olsen | September 7, 2001 | September 27, 2003 | Pitcher | Florida Marlins |
| Ole Olsen | April 12, 1922 | September 24, 1923 | Pitcher | Detroit Tigers |
| Scott Olsen | June 25, 2005 | | Pitcher | Florida Marlins, Washington Nationals |
| Vern Olsen | September 8, 1939 | September 13, 1946 | Pitcher | Chicago Cubs |
| Garrett Olson | July 4, 2007 | | Pitcher | Baltimore Orioles, Seattle Mariners, Pittsburgh Pirates |
| Greg Olson | June 27, 1989 | September 30, 1993 | Catcher | Minnesota Twins, Atlanta Braves |
| Gregg Olson | September 2, 1988 | June 22, 2001 | Pitcher | Baltimore Orioles, Atlanta Braves, Cleveland Indians, Kansas City Royals, Detroit Tigers, Houston Astros, Minnesota Twins, Arizona Diamondbacks, Los Angeles Dodgers |
| Ivy Olson | April 12, 1911 | July 21, 1924 | Shortstop | Cleveland Naps, Cincinnati Reds, Brooklyn Robins |
| Karl Olson | June 30, 1951 | June 10, 1957 | Outfielder | Boston Red Sox, Washington Senators, Detroit Tigers |
| Marv Olson | September 13, 1931 | April 30, 1933 | Second baseman | Boston Red Sox |
| Ted Olson | June 21, 1936 | September 13, 1938 | Pitcher | Boston Red Sox |
| Tim Olson | May 30, 2004 | June 19, 2005 | Utility infielder | Arizona Diamondbacks, Colorado Rockies |
| Ed Olwine | June 2, 1986 | October 2, 1988 | Pitcher | Atlanta Braves |
| Logan Ondrusek | April 5, 2010 | | Pitcher | Cincinnati Reds |
| Ralph Onis | April 27, 1935 | April 27, 1935 | Catcher | Brooklyn Dodgers |
| Eddie Onslow | August 7, 1912 | September 14, 1927 | First baseman | Detroit Tigers, Cleveland Indians, Washington Senators |
| Jack Onslow | May 2, 1912 | October 3, 1917 | Catcher | Detroit Tigers, New York Giants |
| Steve Ontiveros (IF) | August 5, 1973 | June 21, 1980 | Third baseman | San Francisco Giants, Chicago Cubs |
| Steve Ontiveros (P) | June 14, 1985 | October 1, 2000 | Pitcher | Oakland Athletics, Philadelphia Phillies, Seattle Mariners, Boston Red Sox |
| José Oquendo | May 2, 1983 | September 29, 1995 | Second baseman | New York Mets, St. Louis Cardinals |
| Mike Oquist | August 14, 1993 | September 21, 1999 | Pitcher | Baltimore Orioles, San Diego Padres, Oakland Athletics |
| Tom Oran | May 4, 1875 | July 4, 1875 | Outfielder | St. Louis Red Stockings |
| Ernie Oravetz | April 11, 1955 | September 30, 1956 | Outfielder | Washington Senators |
| Luis Ordaz | September 3, 1997 | April 3, 2006 | Shortstop | St. Louis Cardinals, Kansas City Royals, Tampa Bay Devil Rays |
| Tony Ordeñana | October 3, 1943 | October 3, 1943 | Shortstop | Pittsburgh Pirates |
| Magglio Ordóñez | August 29, 1997 | | Outfielder | Chicago White Sox, Detroit Tigers |
| Rey Ordóñez | April 1, 1996 | July 17, 2004 | Shortstop | New York Mets, Tampa Bay Devil Rays, Chicago Cubs |
| Joe Orengo | April 18, 1939 | September 25, 1945 | Utility infielder | St. Louis Cardinals, New York Giants, Brooklyn Dodgers, Detroit Tigers, Chicago White Sox |
| Kevin Orie | April 1, 1997 | September 26, 2002 | Third baseman | Chicago Cubs, Florida Marlins |
| George Orme | September 14, 1920 | September 17, 1920 | Outfielder | Boston Red Sox |
| Jess Orndorff | April 18, 1907 | April 24, 1907 | Catcher | Boston Doves |
| Eddie Oropesa | April 2, 2001 | May 20, 2004 | Pitcher | Philadelphia Phillies, Arizona Diamondbacks, San Diego Padres |
| Jesse Orosco | April 5, 1979 | September 27, 2003 | Pitcher | New York Mets, Los Angeles Dodgers, Cleveland Indians, Milwaukee Brewers, Baltimore Orioles, St. Louis Cardinals, San Diego Padres, New York Yankees, Minnesota Twins |
| Billy Orr | May 3, 1913 | May 22, 1914 | Shortstop | Philadelphia Athletics |
| Dave Orr | May 17, 1883 | October 2, 1890 | First baseman | New York Metropolitans, New York Gothams, Brooklyn Bridegrooms, Columbus Solons, Brooklyn Ward's Wonders |
| Pete Orr | April 5, 2005 | | Utility infielder | Atlanta Braves, Washington Nationals, Philadelphia Phillies |
| Joe Orrell | August 12, 1943 | August 6, 1945 | Pitcher | Detroit Tigers |
| Ernie Orsatti | September 4, 1927 | September 28, 1935 | Outfielder | St. Louis Cardinals |
| John Orsino | July 14, 1961 | September 10, 1967 | Catcher | San Francisco Giants, Baltimore Orioles, Washington Senators (1961–1971) |
| Joe Orsulak | September 1, 1983 | September 25, 1997 | Outfielder | Pittsburgh Pirates, Baltimore Orioles, New York Mets, Florida Marlins, Montreal Expos |
| Jorge Orta | April 15, 1972 | June 10, 1987 | Second baseman | Chicago White Sox, Cleveland Indians, Los Angeles Dodgers, Toronto Blue Jays, Kansas City Royals |
| Anthony Ortega | April 25, 2009 | | Pitcher | Los Angeles Angels of Anaheim |
| Bill Ortega | September 7, 2001 | September 28, 2001 | Pinch hitter | St. Louis Cardinals |
| Phil Ortega | September 10, 1960 | May 4, 1969 | Pitcher | Los Angeles Dodgers, Washington Senators (1961–1971), California Angels |
| Frank Ortenzio | September 9, 1973 | September 30, 1973 | First baseman | Kansas City Royals |
| Al Orth | August 15, 1895 | September 20, 1909 | Pitcher | Philadelphia Phillies, Washington Senators, New York Highlanders |
| Baby Ortiz | September 23, 1944 | September 27, 1944 | Pitcher | Washington Senators |
| David Ortiz | September 2, 1997 | | Designated hitter | Minnesota Twins, Boston Red Sox |
| Héctor Ortiz | September 14, 1998 | May 15, 2002 | Catcher | Kansas City Royals, Texas Rangers |
| Javier Ortiz | June 15, 1990 | October 6, 1991 | Outfielder | Houston Astros |
| José Ortiz (OF) | September 4, 1969 | June 16, 1971 | Outfielder | Chicago White Sox, Chicago Cubs |
| José Ortiz (2B) | September 15, 2000 | September 27, 2002 | Second baseman | Oakland Athletics, Colorado Rockies |
| Junior Ortiz | September 20, 1982 | August 8, 1994 | Catcher | Pittsburgh Pirates, New York Mets, Minnesota Twins, Cleveland Indians, Texas Rangers |
| Luis Ortiz | August 31, 1993 | September 28, 1996 | Third baseman | Boston Red Sox, Texas Rangers |
| Ramón Ortiz | August 19, 1999 | | Pitcher | Anaheim Angels, Cincinnati Reds, Washington Nationals, Minnesota Twins, Colorado Rockies, Los Angeles Dodgers, Chicago Cubs |
| Roberto Ortiz | September 6, 1941 | September 2, 1950 | Outfielder | Washington Senators, Philadelphia Athletics |
| Russ Ortiz | April 2, 1998 | | Pitcher | San Francisco Giants, Atlanta Braves, Arizona Diamondbacks, Baltimore Orioles, Houston Astros, Los Angeles Dodgers |
| Daniel Ortmeier | September 5, 2005 | | Outfielder | San Francisco Giants |
| John Orton | August 20, 1989 | July 4, 1993 | Catcher | California Angels |
| Chad Orvella | May 31, 2005 | | Pitcher | Tampa Bay Devil Rays |
| Ossie Orwoll | April 13, 1928 | August 21, 1929 | Utility player | Philadelphia Athletics |
| Bob Osborn | September 16, 1925 | September 24, 1931 | Pitcher | Chicago Cubs, Pittsburgh Pirates |
| Fred Osborn | June 8, 1907 | July 24, 1909 | Outfielder | Philadelphia Phillies |
| Ozzie Osborn | April 26, 1975 | September 23, 1975 | Pitcher | Chicago White Sox |
| Bobo Osborne | June 27, 1957 | September 24, 1963 | First baseman | Detroit Tigers, Washington Senators (1961–1971) |
| Donovan Osborne | April 9, 1992 | May 15, 2004 | Pitcher | St. Louis Cardinals, Chicago Cubs, New York Yankees |
| Fred Osborne | July 14, 1890 | September 1, 1890 | Outfielder | Pittsburgh Alleghenys |
| Tiny Osborne | April 15, 1922 | September 28, 1925 | Pitcher | Chicago Cubs, Brooklyn Robins |
| Wayne Osborne | April 18, 1935 | May 6, 1936 | Pitcher | Pittsburgh Pirates, Boston Bees |
| Pat Osburn | April 13, 1974 | September 22, 1975 | Pitcher | Cincinnati Reds, Milwaukee Brewers |
| Charlie Osgood | June 18, 1944 | June 18, 1944 | Pitcher | Brooklyn Dodgers |
| Keith Osik | April 5, 1996 | October 1, 2005 | Catcher | Pittsburgh Pirates, Milwaukee Brewers, Baltimore Orioles, Washington Nationals |
| Dan Osinski | April 11, 1962 | April 16, 1970 | Pitcher | Los Angeles Angels, Milwaukee Braves, Boston Red Sox, Chicago White Sox, Houston Astros |
| Franquelis Osoria | June 7, 2005 | July 30, 2008 | Pitcher | Los Angeles Dodgers, Pittsburgh Pirates |
| Harry Ostdiek | September 10, 1904 | October 7, 1908 | Catcher | Cleveland Naps, Boston Red Sox |
| Champ Osteen | September 18, 1903 | May 3, 1909 | Shortstop | Washington Senators, New York Yankees, St. Louis Cardinals |
| Claude Osteen | July 6, 1957 | September 27, 1975 | Pitcher | Cincinnati Redlegs/Reds, Washington Senators (1961–1971), Los Angeles Dodgers, Houston Astros, St. Louis Cardinals, Chicago White Sox |
| Darrell Osteen | September 2, 1965 | July 19, 1970 | Pitcher | Cincinnati Reds, Oakland Athletics |
| Fred Ostendorf | July 16, 1914 | July 16, 1914 | Pitcher | Indianapolis Hoosiers (FL) |
| Bill Oster | August 23, 1954 | September 20, 1954 | Pitcher | Philadelphia Athletics |
| Red Ostergard | June 14, 1921 | August 17, 1921 | Pinch hitter | Chicago White Sox |
| Charlie Osterhout | June 23, 1879 | September 6, 1879 | Catcher/Outfielder | Syracuse Stars (NL) |
| Fritz Ostermueller | April 21, 1934 | September 30, 1948 | Pitcher | Boston Red Sox, St. Louis Browns, Brooklyn Dodgers, Pittsburgh Pirates |
| Jimmy Osting | May 2, 2001 | August 27, 2002 | Pitcher | San Diego Padres, Milwaukee Brewers |
| Brian Ostrosser | August 5, 1973 | August 13, 1973 | Shortstop | New York Mets |
| Joe Ostrowski | July 18, 1948 | August 20, 1952 | Pitcher | St. Louis Browns, New York Yankees |
| Johnny Ostrowski | September 24, 1943 | October 1, 1950 | Outfielder | Chicago Cubs, Boston Red Sox, Chicago White Sox, Washington Senators |
| Al Osuna | September 2, 1990 | September 27, 1996 | Pitcher | Houston Astros, Los Angeles Dodgers, San Diego Padres |
| Antonio Osuna | April 25, 1995 | April 10, 2005 | Pitcher | Los Angeles Dodgers, Chicago White Sox, New York Yankees, San Diego Padres, Washington Nationals |
| Roy Oswalt | May 6, 2001 | | Pitcher | Houston Astros, Philadelphia Phillies |
| Willis Otáñez | August 25, 1998 | October 3, 1999 | Third baseman | Baltimore Orioles, Toronto Blue Jays |
| Reggie Otero | September 2, 1945 | September 29, 1945 | First baseman | Chicago Cubs |
| Ricky Otero | April 26, 1995 | August 17, 1997 | Outfielder | New York Mets, Philadelphia Phillies |
| Bill Otey | September 27, 1907 | June 24, 1911 | Pitcher | Pittsburgh Pirates, Washington Senators |
| Amos Otis | September 6, 1967 | August 5, 1984 | Outfielder | New York Mets, Kansas City Royals, Pittsburgh Pirates |
| Bill Otis | July 4, 1912 | July 6, 1912 | Outfielder | New York Highlanders |
| Harry Otis | September 5, 1909 | September 29, 1909 | Pitcher | Cleveland Naps |
| Akinori Otsuka | April 6, 2004 | July 1, 2007 | Pitcher | San Diego Padres, Texas Rangers |
| Billy Ott | September 4, 1962 | July 14, 1964 | Outfielder | Chicago Cubs |
| Ed Ott | June 10, 1974 | October 2, 1981 | Catcher | Pittsburgh Pirates, California Angels |
| Mel Ott β | April 27, 1926 | July 11, 1947 | Outfielder | New York Giants |
| Adam Ottavino | May 29, 2010 | | Pitcher | St. Louis Cardinals |
| Jim Otten | July 31, 1974 | September 30, 1981 | Pitcher | Chicago White Sox, St. Louis Cardinals |
| John Otten | July 5, 1895 | September 28, 1895 | Catcher | St. Louis Browns (NL) |
| Billy Otterson | September 4, 1887 | October 10, 1887 | Shortstop | Brooklyn Grays |
| Dave Otto | September 8, 1987 | August 10, 1994 | Pitcher | Oakland Athletics, Cleveland Indians, Pittsburgh Pirates, Chicago Cubs |
| Phil Ouellette | September 10, 1986 | October 3, 1986 | Catcher | San Francisco Giants |
| Johnny Oulliber | July 25, 1933 | October 1, 1933 | Outfielder | Cleveland Indians |
| Chink Outen | April 16, 1933 | October 1, 1933 | Catcher | Brooklyn Dodgers |
| Jimmy Outlaw | April 20, 1937 | May 8, 1949 | Outfielder | Cincinnati Reds, Boston Bees, Detroit Tigers |
| Josh Outman | September 2, 2008 | | Pitcher | Oakland Athletics |
| Orval Overall | April 16, 1905 | July 29, 1913 | Pitcher | Cincinnati Reds, Chicago Cubs |
| Lyle Overbay | September 19, 2001 | | First baseman | Arizona Diamondbacks, Milwaukee Brewers, Toronto Blue Jays, Pittsburgh Pirates |
| Stubby Overmire | April 25, 1943 | August 3, 1952 | Pitcher | Detroit Tigers, St. Louis Browns, New York Yankees |
| Mike Overy | August 14, 1976 | September 9, 1976 | Pitcher | California Angels |
| Ernie Ovitz | June 22, 1911 | June 22, 1911 | Pitcher | Chicago Cubs |
| Bob Owchinko | September 25, 1976 | October 1, 1986 | Pitcher | San Diego Padres, Cleveland Indians, Oakland Athletics, Pittsburgh Pirates, Cincinnati Reds, Montreal Expos |
| Dave Owen | September 6, 1983 | October 2, 1988 | Shortstop | Chicago Cubs, Kansas City Royals |
| Frank Owen | April 29, 1901 | May 12, 1909 | Pitcher | Detroit Tigers, Chicago White Sox |
| Larry Owen | August 14, 1981 | September 25, 1988 | Catcher | Atlanta Braves, Kansas City Royals |
| Marv Owen | April 16, 1931 | August 2, 1940 | Third baseman | Detroit Tigers, Chicago White Sox, Boston Red Sox |
| Mickey Owen | May 2, 1937 | September 11, 1954 | Catcher | St. Louis Cardinals, Brooklyn Dodgers, Chicago Cubs, Boston Red Sox |
| Spike Owen | June 25, 1983 | October 2, 1995 | Shortstop | Seattle Mariners, Boston Red Sox, Montreal Expos, New York Yankees, California Angels |
| Eric Owens | June 6, 1995 | September 27, 2003 | Outfielder | Cincinnati Reds, Milwaukee Brewers, San Diego Padres, Florida Marlins, Anaheim Angels |
| Henry Owens | July 7, 2006 | | Pitcher | New York Mets, Florida Marlins |
| Jack Owens | September 21, 1935 | September 22, 1935 | Catcher | Philadelphia Athletics |
| Jayhawk Owens | June 6, 1993 | September 28, 1996 | Catcher | Colorado Rockies |
| Jerry Owens | September 11, 2006 | | Outfielder | Chicago White Sox |
| Jim Owens | April 19, 1955 | June 20, 1967 | Pitcher | Philadelphia Phillies, Cincinnati Reds, Houston Colt .45s/Astros |
| Red Owens | July 28, 1899 | May 31, 1905 | Second baseman | Philadelphia Phillies, Brooklyn Superbas |
| Yip Owens | September 11, 1905 | October 3, 1915 | Catcher | Boston Americans, Chicago White Sox, Brooklyn Tip-Tops, Baltimore Terrapins |
| Micah Owings | April 6, 2007 | | Pitcher | Arizona Diamondbacks, Cincinnati Reds |
| Rick Ownbey | August 17, 1982 | July 3, 1986 | Pitcher | New York Mets, St. Louis Cardinals |
| Henry Oxley | July 30, 1884 | October 10, 1884 | Catcher | New York Gothams, New York Metropolitans |
| Chris Oxspring | September 2, 2005 | September 17, 2005 | Pitcher | San Diego Padres |
| Andy Oyler | May 8, 1902 | July 21, 1902 | Third baseman | Baltimore Orioles (1901–02) |
| Ray Oyler | April 18, 1965 | October 1, 1970 | Shortstop | Detroit Tigers, Seattle Pilots, California Angels |
| Doc Ozmer | May 11, 1923 | May 11, 1923 | Pitcher | Philadelphia Athletics |
| Pablo Ozuna | April 23, 2000 | | Utility player | Florida Marlins, Colorado Rockies, Chicago White Sox, Los Angeles Dodgers |